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4th year project
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Internet Mobile RobotThe Quadcopter
Group 13Rahul Bura
Mohamed ChandeVinayak Goge
Hue Vo
Supervisor: Professor Peter X. Liu
A report submitted in partial fulfillment of the requirements of SYSC-4907 Engineering Project
Department of Systems and Computer EngineeringFaculty of Engineering
Carleton University
April 7, 2010
April 7th, 2010
AbstractGroup 13 consisting of Rahul Bura, Mohamed Chande, Vinayak Goge and Hue Vo have
developed a start-up project as a partial fulfillment for SYSC 4907 Engineering Project: Internet
Mobile Robot: The Quadcopter. The objective of the project was to design and implement a
Quadcopter (helicopter with four propellers) that can take flight and be controlled using a
remote client application over the internet.
Currently, different Quadcopter designs have been implemented. However, most of
them have used handheld Radio Control implementations. With the design implemented in this
project, different applications can be developed to control the Quadcopter over the internet
from a remote location. This opens up different possibilities with the design being applied in
different areas ranging from Surveillance to Virtual Gaming Technologies to Military
Applications.
Different designs were explored and from these designs, it was determined that we
would need a microcontroller to run control algorithms, a Wi-Fi chip to facilitate wireless
communication and a webpage to for user interaction. Any command received from the WI-Fi
chip is processed by the microcontroller and executed by all the components including motors,
speed controllers and inertial measurement units that are used to stabilize the Quadcopter.
The communication system implemented a server/client architecture with the Wi-Fi
chip behaving as a server that acts to reply to requests from a remote client webpage. For the
data transfer mechanism, TCP protocol was used over the Internet to send traffic from the
client to the server and bidirectionally. The webpage, implemented as a simple Graphical User
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April 7th, 2010
Interface (GUI), is a good replacement for the RC handheld devices and allows for easy
portability from one client to another.
Department of Systems and Computer Engineering |Carleton University 2
April 7th, 2010
AcknowledgementsWe would like to formally thank Professor Peter X. Liu for supervising and for his
guidance throughout the Internet Mobile Robot project as well as giving us the opportunity to
explore and experiment with our creativity.
We would also like to thank the Technical Support Staff, Danny Lemay, Jerry Buburuz
and Daren Russ, for their support throughout the project. Their prompt actions, experience
and knowledge allowed us to surpass various milestones throughout the duration of the
project.
Department of Systems and Computer Engineering |Carleton University 3
April 7th, 2010
Table of Contents
Abstract.................................................................................................................................... i
Acknowledgements................................................................................................................iii
List of Figures..........................................................................................................................vi
List of Tables.........................................................................................................................viii
1.0 Introduction.....................................................................................................................11.1 Background.................................................................................................................11.2 Motivation..................................................................................................................31.3 Problem Statement.....................................................................................................31.4 Proposed Solution and Accomplishments..................................................................31.5 Overview of the Remainder of the Report..................................................................6
2.0 The Engineering Project...................................................................................................82.1 Health and Safety.......................................................................................................82.2 Engineering Professionalism.......................................................................................92.3 Project Management................................................................................................102.4 Individual Contributions...........................................................................................11
2.4.1 Project Contributions........................................................................................112.4.2 Report Contributions........................................................................................12
3.0 Robot Design.................................................................................................................133.1 Structure...................................................................................................................13
3.1.1 Number of Motors............................................................................................133.1.2 Frame................................................................................................................15
3.2 Communications.......................................................................................................153.3 Flight and Stability....................................................................................................163.4 Flight Control............................................................................................................183.5 Power.......................................................................................................................20
4.0 Hardware Components and Construction.....................................................................224.1 Frame and Structure.................................................................................................224.2 Microcontroller.........................................................................................................244.3 Flight and Stability....................................................................................................25
4.3.1 Propeller and Motor Combination Configuration.............................................254.3.2 Electronic Speed Controller (ESC).....................................................................264.3.3 Six Degrees of Freedom (DOF)..........................................................................27
4.4 Communications.......................................................................................................284.5 Battery......................................................................................................................28
4.5.1 Flight Time and Battery Power Dependancy.....................................................294.6 Design Implementation and Final Structure.............................................................30
5.0 Stability and Manoeuvre................................................................................................335.1 Filtering Noise...........................................................................................................33
5.1.1 Noise Reduction................................................................................................33
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April 7th, 2010
5.1.2 Second Order Complementary Filter................................................................345.2 Feedback Control......................................................................................................35
5.2.1 Six Degrees of Freedom (DOF)..........................................................................365.2.2 System Control Theory......................................................................................375.2.3 Proportional, Integral, Derivative Controller.....................................................405.2.4 Feedback Control Mechanism: Inertial Measurement Units.............................425.2.5 Feedback Control Loop.....................................................................................435.2.6 Flight Tuning Using Ziegler-Nichols Rules..........................................................45
5.3 Flight Configuration and Simulation.........................................................................465.3.1 Flight Configuration Methods and Tools...........................................................465.3.2 Pre-Flight Tests..................................................................................................495.3.3 Flight Control and Results.................................................................................50
6.0 Wireless Communication (Server).................................................................................546.1 Communication System Overview............................................................................546.2 Wireless Standards...................................................................................................55
6.2.1 ZigBee...............................................................................................................566.2.2 Wi-Fi..................................................................................................................57
6.3 WiShield Configurations...........................................................................................586.3.1 Network Type....................................................................................................586.3.2 TCP vs UDP........................................................................................................59
6.4 WiShield Functionality..............................................................................................646.5 Serial Peripheral Interface........................................................................................666.6 Challenges and Solutions..........................................................................................69
6.6.1 Debugging.........................................................................................................696.6.2 Pin Conflict........................................................................................................71
7.0 Wireless Communication (Client)..................................................................................737.1 Client Design.............................................................................................................737.2 Client Process...........................................................................................................77
8.0 User Interface................................................................................................................798.1 Software Requirements............................................................................................80
8.1.1 Operating System..............................................................................................818.1.2 XAMPP..............................................................................................................81
8.2 Challenges and Solutions..........................................................................................83
9.0 Software Integration......................................................................................................85
10.0 Production Expenses......................................................................................................8810.1 Material Costs...........................................................................................................88
11.0 Conclusion and Recommendations................................................................................9011.1 Conclusion................................................................................................................9011.2 Recommendations....................................................................................................92
References.............................................................................................................................93
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April 7th, 2010
List of FiguresFigure 1: Rotating pairs of rotors [3]...............................................................................................1
Figure 2: First Generation Design of De Bothezat Quadrotor [3]....................................................2
Figure 3: Wound Rotor [10]..........................................................................................................16
Figure 4: Brushless Motor Design [11]..........................................................................................17
Figure 5: Typical Microcontroller..................................................................................................19
Figure 6: Sketch of Proposed Structure........................................................................................23
Figure 7: Initial Frame...................................................................................................................23
Figure 8 : Aeroquad Shield............................................................................................................28
Figure 9: Graph of Flight Time versus Battery Life........................................................................30
Figure 10: Wiring Diagram for IMR...............................................................................................31
Figure 11: Final Design..................................................................................................................32
Figure 12: Second Order Complementary Filter [15]....................................................................34
Figure 13: Second Order Complementary Filter [15]....................................................................35
Figure 14: Possible independent movements in 3D space [16]....................................................37
Figure 15: Types of Control Systems: (a) Open Loop (b) Feed-Forward (c) Closed Loop [18].......38
Figure 16: How the damping constant affects the time it takes to reach steady state [19]..........40
Figure 17: PID Controller loop [20]...............................................................................................42
Figure 18: Feedback loop including system, controller and sensor configuration [21].................43
Figure 19: Feedback Control Loop with control components.......................................................44
Figure 20: Motor Command outputs (S) during simulation of flight with Serial Monitor.............46
Figure 21: Sensor Data output (Q) during simulation of flight with Serial Monitor......................47
Figure 22: AeroQuad Configurator GUI with updatable flight parameters...................................48
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April 7th, 2010
Figure 23: Various sensor outputs with AeroQuad Configurator GUI...........................................49
Figure 24: Original Communication System Design......................................................................55
Figure 25: TCP three-way handshake...........................................................................................60
Figure 26: Re-designed Communication System...........................................................................63
Figure 27: WiShield Functionality.................................................................................................64
Figure 28: Handling TCP connection.............................................................................................65
Figure 29: SPI bus, single-master single-slave...............................................................................67
Figure 30: WiShield Schematic [27]..............................................................................................68
Figure 31: Simple Compiler provided for WiShield.......................................................................71
Figure 32: Ideal Layout of Client System in relation with WiShield...............................................74
Figure 33: Actual Implementation of Client System in relation with Wi-Shield............................75
Figure 34: Client Design................................................................................................................76
Figure 35: Client Process...............................................................................................................78
Figure 36: User Interface..............................................................................................................79
Figure 37: Components of the User Interface...............................................................................80
Figure 38: Pin 5 of SM (with WiShield) connected to digital pin 32 of PM using a wire [39]........87
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April 7th, 2010
List of TablesTable 1: Report Contributions......................................................................................................12
Table 2: Flight Times for 2 Different Designs................................................................................14
Table 3: Matching Motors for EPP1045 Propeller.........................................................................25
Table 4: Total Weight Calculation.................................................................................................29
Table 5: PID gain using Ziegler-Nichols Tuning Rule [17]..............................................................45
Table 6: Values of KP and corresponding qualitative observations for Ziegler-Nichols Rule.........52
Table 7: Relevant differences between TCP and UDP...................................................................62
Table 8: List of Materials and Respective Cost..............................................................................89
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1.0 IntroductionWith the recent developments in wireless communications technology and its
increased accessibility and affordability, network-based applications are now able to
expand into new areas. One of these areas is the domain of Internet Robots. Internet
robots have numerous applications and they can be programmed to perform multiple
functions. The Internet Mobile Robot (IMR) constructed is an Unmanned Aerial Vehicle
(UAV) that will be controlled wirelessly via a web browser.
1.1 Background
The Unmanned Aerial Vehicle built is also known as
a Quadcopter or Quadrotor owing to the fact that it has
four motors and propellers that stabilize and manoeuvre
the robot. Flight control is achieved by varying the speed of
each rotor to change the thrust and torque about the
center of rotation. The rotors are spinning in pairs of
angular velocity - two rotate clockwise and two rotate counter-clockwise. This is
illustrated in Figure 1.
Quadcopters have been around for a while and its development can be generally
classified into 2 generations. The first generation of designs were done to transport
cargo and passengers. However, early prototypes suffered from poor performance [1]
and latter prototypes required too much pilot workload, due to poor stability [2].
Department of Systems and Computer Engineering |Carleton University 1
Figure 1: Rotating pairs of rotors [3]
April 7th, 2010
Figure 2: First Generation Design of De Bothezat Quadrotor [3]
The second generation of Quadcopter designs is what the Internet Mobile Robot
falls under. This more recent generation consists of designs that are commonly designed
to be unmanned aerial vehicles that use electric control systems and sensors to stabilize
the aircraft [4]. There are various advantages of the current generation of Quadrotors
over comparable scale helicopters. Quadrotors have a simpler mechanism that controls
the rotor blades as opposed to a helicopter’s as mechanical linkages are not required for
control of the rotor blades. This simplifies the design of the vehicle, and reduces
maintenance time and cost [5]. Also, the use of four rotors allows each individual rotor
to have a smaller diameter than the equivalent helicopter rotor resulting in less kinetic
energy being stored during flight. This reduces the damage caused should the rotors hit
any objects. For small scale vehicles, this makes it safer to interact with in close
proximity. Finally, by enclosing the rotors within a frame, the rotors can be protected
during collisions, permitting flights indoors and in obstacle-dense environments, with
low risk of damaging the vehicle, its operators, or its surroundings [6].
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April 7th, 2010
1.2 Motivation
Multiple implementations of the Quadcopter currently exist. However, most of
them are Radio Control (RC) implementations. Having a Wi-Fi implementation would
open up the communications to other possibilities. Adopting this implementation
would mean that we would be abolishing the use of the traditional RC remote
controller. In lieu of this, a control mechanism needs to be created in the form of an
encrypted web browser with a user-friendly Graphical User Interface (GUI). Also, there
are various methods to stabilize the RC Quadcopter using accelerometers and
gyroscopes. Having chosen to adopt a Wi-Fi implementation, these methods need to be
studied and adapted to the Wi-Fi implementation.
1.3 Problem Statement
A Quadcopter needs to be constructed and a Wi-Fi implementation needs to be
done to wirelessly manoeuvre and stabilize it via the internet, through a web browser.
1.4 Proposed Solution and Accomplishments
As can be seen from Section 1.3, there were four main areas that this project
concerned itself with. The first goal was to get a Quadcopter, comprising of the
structure and control logic, constructed. Having done so, a Wi-Fi implementation has to
be deployed to control the system. This system then needs to achieve stability and
stable manoeuvrability. A user control interface also needs to be developed to control
the system in the form of a secure web page.
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April 7th, 2010
The Quadcopter can be constructed using various component parts from hobby
shops. Major parts to look at would be the robot’s frame as well as the robot’s flight and
control mechanism. A major accomplishment was determining the various required
parts and where we could procure them. Having done much preliminary research, a big
contribution to the project, the components were purchased from various online stores.
The construction of the structure itself was an important accomplishment as it was a
necessary component for testing this year. It will be just as important a component for
future groups working on this project as it will be foundation on which further
applications can be developed. The initial design was constantly modified to meet
changing needs. More can be read in Sections 3.0 and 4.0 regarding the selection of
components and the design and implementation process.
The Wi-Fi implementation can be achieved by using a Wi-Fi module that can
communicate remotely with the router. An accomplishment was to find the right Wi-Fi
module to communicate with the robot remotely via a router. The WiShield from Async
Labs was purchased for this purpose. Commands that the Wi-Fi module receives are
communicated to the microcontroller making the robot correspond respectively. This
was achieved by learning the various communication protocols (TCP and UDP) and
selecting the appropriate protocol. A good understanding of the extensive
documentation that came with the module was also necessary and can be seen as an
accomplishment since we are now able to write code (client / server) for this module
knowing which functions we would utilize. It is an even greater accomplishment that we
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April 7th, 2010
were able to achieve Wi-Fi controllability as the WiShield is one of the first modules of
its kind and there was neither support nor a debugging mechanism available. Section 6.0
covers this in detail.
Extensive research was done to determine the means to achieve stability of the
IMR. Results showed that stability can be achieved using an Inertial Measurement Unit
(IMU) and a Proportional-Integral-Derivative (PID) controller. The IMU is the hardware
component and the PID controller is the software component that complements the
IMU. Two chips work in tandem to provide a Six Degree Of Freedom (6DOF) IMU. The
IMU generates raw accelerometer and gyroscope data that are fed to a filter as inputs
so that the speed of the motors can be varied accordingly to stabilize the Quadcopter.
The Quadcopter is able to stabilize fairly well using this implementation although more
testing and debugging needs to be done for this implementation to work flawlessly. Due
to time constraints, we were unable to get the Quadcopter completely stable. We were
however able to identify why the Quadcopter is unable to completely stabalize itself and
this is a key contribution to the project this year so that future teams are saved from
looking for causes. Section 5.0 can be referred for further details regarding stability. The
PID Controller was just one component of the code required for the proper control of
the IMR and hence another major contribution this year was to have a good
understanding of the various component functions required for the proper operation of
the IMR.
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April 7th, 2010
A web browser- based GUI was developed using a suite of scripting languages.
One accomplishment was to determine which languages needed to be used to build this
interface. After much research XAMPP package was selected due to its ability to
facilitate various interfacing as well as the potential for further development in the
future. After having chosen this package, another major accomplishment was the design
of the interface. This design is not perfect but it’s a good foundation for future designs.
It outlines the basic controls currently but this can be improved upon in the future to
provide visual feedback, a battery monitor, telemetry etc. according to future
development of the IMR. Further details can be read in Section 8.0.
Another major accomplishment was the integration of all the code so that the
IMR can function seamlessly. The current solution was implemented successfully
however it is not the most elegant solution. Section 9.0 has more information with
regards to this.
1.5 Overview of the Remainder of the Report
The remainder of the report consists of documents that constitute research
needed for the IMR project. These documents may be in the form of code, calculations,
charts or graphs that illustrate or aid in the understanding of a concept or point. Graphs,
figure and tables will be referred to in the pertinent paragraphs, by their corresponding
numbers. The List of Figures and List of Tables on pages 6 and 8 respectively can be
referred to as well.
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April 7th, 2010
Section 3.0 will expound on the process of designing the IMR. It will outline the
research and calculations done to come to the final design of the IMR as well as the
component parts. Section 4.0 is complementary to Section 3.0 and it will outline the
components chosen and the rationale behind each selection. It will also briefly touch on
the construction process of the IMR.
Section 5.0 will go into further detail on stability and system controls. The
section will delve deeper into topics such as noise-handling, filters and filtering as well
as feedback loops and the control mechanism that was used to control the IMR.
Section 6.0, Section 7.0 and Section 8.0 constitute materials on the
communications component of the project. Section 6.0 looks into how commands are
communicated to the IMR. It will look at how the Wi-Fi module has been utilised and
how the functions were implemented to communicate wirelessly with the IMR. Section
7.0 describes the client process and Section 8.0 comprises of material on how the user
can communicate with the IMR via the GUI created. It also looks at how the GUI was
implemented.
Section 9.0 explains the software integration process and Section 10.0 provides
information on the materials purchased. Section 11.0 concludes the report by looking at
what we’ve achieved this year. It is going to briefly outline the accomplishments and
detail various recommendations for future project groups working on the Quadcopter.
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April 7th, 2010
2.0 The Engineering Project
2.1 Health and Safety
Due to the nature of the project, there are many health and safety concerns that
one should be aware of before working on such a project. These concerns range from
health concerns possibly causing bodily harm to oneself as well as others. Many
measures were taken to ensure the health and safety of all members as well as other
throughout the span of the project.
As with most engineering projects, a lot of time is spent in front of a computer
whether it be for research and analysis or for the implementation aspect. Many health
concerns can arise if one spends an extended period of time in front of the computer.
Sitting with poor posture can cause back pains and wrist pains and staring at a screen for
too long may cause one’s eyes to strain. As such, it is recommended to take regular
breaks to not over strain the eyes and to not cause future back or posture problems.
Specific to this project, there are large propellers slicing through the air and a
mass flying from point to point. Anytime there are large moving parts that can cause
minor to severe bodily harm, one should take safety precautions. Although the
propellers are plastic, the speed at which it is rotating is enough to penetrate the skin.
Before commencing with any tests or attaching the propellers and allowing them to
spin, one should ensure that there is no one and nothing in the vicinity of the propellers.
Also, it is recommended to test in an open space with plenty of room in case one should
lose control of the Quadcopter. For testing purposes, the Quadcopter should be
powered using the Power Supply until consistent wireless connection and
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April 7th, 2010
communication to the Arduino can be established. This way, there is always a method
of turning off the Quadcopter should it start to fly in an unexpected manner. Once the
wireless connection can be proven to be reliable, one can use the battery to test the
Quadcopter.
When working with electrical devices, there can always be a risk of shock or even
electrocution. It is extremely important to take precautions when handling electrical
components and power supplies. Ensure that everyone that must come in contact with
the components know the risks and the proper method of handling the components.
Any soldering done should be done with proper equipment and technique. There are
guidelines at each soldering station in the labs. One should read and understand how to
properly handle the equipment before attempting to solder as this can lead to severe
burns.
2.2 Engineering Professionalism
Engineering is a profession. It is the process of methodically and logically coming
up with a solution for a given problem. As part of the requirements for graduation, our
team has formally respected all phases of a development cycle. For it to be considered
engineering there must have been some research and analysis of a problem. A solution
was then supplied in the form of a Proposal. Further research and analysis was done
before the design phase of the project, followed by an interim/progress report (and
presentation). Then there was a period of implementation and testing. The team has
followed the procedures and are coming to the end of the development cycle for the
proposed project.
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April 7th, 2010
Throughout the project, our group made sure our decisions were made
responsibly and took precautions to ensure no one in the immediate society would be
harmed during the testing and development of the project. Should any doubts arise
about the potential safety of anyone, measures were taken to relieve that doubt.
Internally, as a team, each group member has handled themselves
professionally. In the case of a disagreement, the team would get together and discuss
civilly to find a compromise. We have made decisions for the benefit of the progress of
the project without attempting anything that may be considered immoral or unethical.
Each member took ownership of their duties and ensured that their work was
completed as well as it could be.
2.3 Project Management
Our team started our development by doing some research on our topic of
interest. After some brainstorming sessions for possible ideas, we proceeded with our
Quadcopter idea and did some further research and analysis on the topic including
possible structure design and components. The brainstorming session really brought
together the idea and laid a path for the direction we wanted the project to head in.
As the project progressed, different components were selected and designated
to a “primary” that will be responsible for that component from then forward. These
topics were chosen to be relatively independent of each other to allow each member to
develop an expertise in that topic and allow for a specific area of work while working
independently.
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April 7th, 2010
Team meetings were made regularly to discuss the progress and any problems
encountered. Should a problem arise, the team would help in finding a solution or
suggest any possible alternatives. Any major changes in the direction of the project
would then be discussed and agreed upon. Deadlines for both the department as well
as internal team deadlines were emphasized and any upcoming events would be
brought up to ensure all team members were aware of their responsibilities for that
deadline. Internal team deadlines were made to ensure progress was made in a timely
manner. Changes to the project were also made in order to meet deadlines as required.
It was decided that only the core components be done for this year, which removed
many additional features we previously wanted to implement.
We also created an online group with Google Groups to allow every member to
add and access any documents another member may be using. This helped with
organizing documents and reports as well as allowed us to share any useful information
with the group in a well managed, designated area. It quickly became a good source for
referencing any previous discussions and documents.
2.4 Individual Contributions
2.4.1 Project Contributions
The area of expertise and designated work was assigned as stated below. The project
could be divided into four high level components:
1. Structural Analysis and Design (Rahul Bura)
2. Stability and Manoeuvre (Hue Vo)
3. Wireless Communication (Mohamed Chande – Server, Vinayak Goge – Client)
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4. User Interface and Webpage Design (Vinayak Goge)
The work was assigned as such in order to allow for any additional required
independent work to be done outside of team meeting times. Much of the work in the
development cycle, from Research and Analysis to Implementation to Component Testing, were
done as a team where suggestions and any further knowledge of the topic by other teammates
could help progress the project more efficiently.
Much of the Research and Analysis was done by all members of the team with Rahul
Bura leading the structural and component selection. During integration of the project, all
members were equally involved, regardless whose component was being integrated at the time.
For formal presentations, all members contributed in different components throughout the
presentation preparation period.
2.4.2 Report Contributions
As with the Project Contributions, as previously stated, this report was written by the
person with the most expertise of the topic throughout the project, as much as possible. The
formal contributions are as follows:
Section Author Editing and Proof Reading1.0 Rahul Bura Mohamed Chande2.0 Hue Vo Vinayak Goge3.0 Rahul Bura Hue Vo4.0 Rahul Bura Mohamed Chande5.0 Hue Vo Rahul Bura6.0 Mohamed Chande Vinayak Goge7.0 Vinayak Goge Mohamed Chande8.0 Vinayak Goge Hue Vo9.0 Mohamed Chande, Hue Vo Rahul Bura
10.0 Rahul Bura, Vinayak Goge Mohamed Chande
11.0 Rahul Bura, Mohamed Chande, Vinayak Goge, Hue Vo
Rahul Bura, Mohamed Chande, Vinayak Goge, Hue Vo
Table 1: Report Contributions
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April 7th, 2010
3.0 Robot DesignRobot design is one of the key components of the project. The IMR consists of
the structure and logic elements. The structure designs were considered based on
manoeuvrability, aerodynamics, and cost of component parts and feasibility of the
design. The logic elements were chosen on the design decisions made to address the
problem statement. The design process took into consideration key components that
include structure of the robot, communications, the stability mechanism, the controls
mechanisms and power.
3.1 Structure
The structure is one half of the IMR. The structure houses the microcontroller
and also has the flight mechanism integrated. Designing the structure design required
various design considerations including the number of motors and frame design.
3.1.1 Number of Motors
Technically, any number of motors can be mounted to achieve flight. However,
with every new motor mounted, the weight of the robot increases. Weight is obviously
a concern and we want the IMR to be as light as possible. There are two types of weight-
weight of the IMR with the basic components mounted components and weight of extra
mounted parts, also known as payload. It is important to note the correlation between
the weight of the IMR , its ability to carry that weight and the number of motors. Table 2
tabulates these factors to help with the design decision. 2 designs were considered - the
Quadcopter (4 motors) and the Octcopter (8 motors) as is reflected in the table.
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The metric used to determine the design is flight time and a 2100mAh battery
was used as a constant power source to determine the flight times for all the payloads
of each of the two designs. It is assumed that each design is able to carry its own
structural weight and hence they are ignored so only the payload is tabulated.
Table 2: Flight Times for 2 Different Designs
As can be observed, with no payload, the Quadcopter can achieve flight for
about 20 minutes and the Octocopter can achieve flight for about 12 minutes. This
demonstrates the effect of the weight of Octocopter’s frame. It has a decreased time of
flight compared to the Quadcopter without a payload. The maximum payload that the
Quadcopter can carry is 24oz for a period of 7.3 minutes. This is in contrast to the 40oz
that the Octocopter can carry due to the increased number of motors. However, it can
only sustain flight for about 4.6 minutes which is not ideal. We also expect that the
maximum payload we will have would be less then 16oz. Hence looking at the payload
Department of Systems and Computer Engineering |Carleton University 14
Pay Load(oz)
4 Motors Design
(Quadcopter)
8 Motors Design
(Octocopter)
0 19.9 11.7 Flight Time (M
ins)
8 12.6 9.2
16 9.2 7.5
24 7.3 6.3
32 - 5.3
40 - 4.6
April 7th, 2010
of 16oz, the Quadcopter offers a better performance and we settled on the four-motor
design for our IMR.
3.1.2 Frame
The frame of the Quadcopter was next in the design of the structure. Numerous
materials were researched with the criteria that the material be durable and light.
Some of the alternatives considered were aluminum, balsa wood and carbon fibre
reinforced plastic. Aluminum is a soft, durable, lightweight and malleable metal that is
easy to work with. It has about one-third the density and stiffness of steel making it
significantly lighter [7]. Balsa wood is one of the lightest varieties of wood available and
strong for its weight, pound for pound. It’s fairly malleable without compromising its
strength [8]. Carbon fibre reinforced plastics are composite plastics that have been
reinforced with carbon fibre to provide a high strength-to-weight ratio. The density of
carbon fiber is also considerably lower than the density of steel, making it ideal for
applications requiring low weight [9].
The design of the frame itself was based on other models. It was decided that
we’ll have a cross-shaped frame with a motor mounted on each of the four arms. The
intersection in the middle would have the logic and power units mounted on it. The
illustration in Figure 6 shows the preliminary proposed structure.
3.2 Communications
How we communicated with the robot was a key consideration. Various
alternatives we looked at including ZigBee, Wi-Fi and Bluetooth. After careful analysis of
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the specifications and capabilities of each technology, we decided on implementing Wi-
Fi for our robot design.
Bluetooth technology however was ruled out earlier in the course of
development of the project mainly because of the cost to transmission range trade-offs.
Bluetooth modules can provide transmission ranges of 1m, 10m and 100m. For our
project purposes, the ideal minimum range was considered to be 100m. With this range,
Bluetooth technology is very expensive. Furthermore, compared to Wi-Fi and ZigBee,
Bluetooth networking is slower and this feature is undesirable in real-time applications
and applications that are sensitive to network delays.
ZigBee, Wi-Fi standards and their corresponding Radio Frequency (RF) modules
provide specifications that meet the requirements of the project. As to how Wi-Fi was
selected over ZigBee, a detailed explanation is provided in Section 6.2.
3.3 Flight and Stability
For flight, four pairs of propellers and motors are required. There are numerous
motors available that are powered by DC or AC sources. We were particularly interested
in DC motors since we wanted to power components using battery cells. DC motors run
on DC electric power and there are various types that include the Brushed DC motors
and Brushless DC Motors.
Brushed motors refer to the classic DC motor that has a wound
rotor with a split ring commutator which periodically reverses the
current direction between the rotor and the external circuit, and a Department of Systems and Computer Engineering |Carleton University 16
Figure 3: Wound Rotor [10]
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magnet stator. [10] An electrical power source is connected to the rotor through the
commutator and its brushes providing current flow and subsequent electromagnetism.
With the commutator switching currents periodically as the rotor turns, the magnetic
poles of the rotor are prevented from ever being fully aligned with the magnetic poles
of the stator field causing the rotor to spin indefinitely. Essentially, stationary metal
contacts that ‘brush’ against moving metallic contacts are used to transfer electrical
energy to coils on the rotor. However, the brushed implementation has a number of
limitations. Main ones include a limit to the maximum speed of the machine and the
need for replacing the brushes.
The alternative is the brushless motor.
The brushless motor’s implementation differs
from that of the brushed motors. A brushless
motor consists of stationary coils and a rotating
magnet. The need for brushes to provide current
to the moving rotor is eliminated and instead an
external electronic controller is used to power up the stationary coils, which are
grouped in phases, causing the magnet to rotate. [11] Section 4.3.2 contains further
discussion on the electronic controller. Figure 4 shows the brushless motor design. The
star-shaped component with the blue coils is the rotor and the disk in the top right
corner has the permanent magnet in the shape of a ring and it rotates around the rotor,
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Figure 4: Brushless Motor Design [11]
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about the centre. This design differentiation provides several advantages over the
brushed motors.
Research showed that an ultimate combination of motor and propeller is needed
to be used for optimal thrust power. The appropriate combination was chosen as can be
seen in Section 4.2.
A 6 degree of Freedom (DOF) Inertial Measurement Unit (IMU) was required for
stability and manoeuvring the Quadcopter. An IMU is an electronic device that measure
and reports velocity, orientation and gravitational forces using accelerometers and
gyroscopes in tandem. Accelerometers measure acceleration relative to freefall and
gyroscopes measure or maintain orientation, based on the principles of conservation of
angular momentum [12]. Since the Quadcopter is going to be flying in a three-
dimensional space, an IMU that considered the 6 degrees of freedom was essential. The
6 degrees of freedom refers to the fact that the rigid body is able to move about the X, Y
and Z axes independent of each of the 3 axes and of the rotation about any of the 3
axes. This would enable the Quadcopter to move forward, backward, up, down as well
as left and right in three-dimensional space.
3.4 Flight Control
To control the Quadcopter, two alternatives were considered. We could have
used a Field-Programmable Gate Array (FPGA) board or a microcontroller. A FPGA is an
integrated circuit that contains programmable logic components known as Logic Blocks
and a hierarchy or reconfigurable interconnects that allows the blocks to be connected.
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These configurations can be programmed using Hardware Description Language (HDL).
However, an FPGA would have been harder for us to work with as we were not as
familiar with it as we are with our other alternative – the microcontroller.
Microcontrollers are computer systems on a chip. Microcontrollers have a
microprocessor and peripheral functions like a relatively simple clock, timers, I/O ports
and memory implemented on one chip. Figure 5 illustrates this. Microcontrollers are
designed for smaller or more dedicated applications and hence they may have lower
clock rate frequencies enabling lower power consumptions. This would be perfect for
battery-powered applications such as our Quadcopter. Microcontrollers were originally
programmed in assembly language (low level language – communication at machine
level) but various high level programming languages are now in use as well. Such
languages can be specially written to be microcontroller-specific or be versions of
general purpose languages such as the C programming language. Compilers and
environments may be tools that are provided by the microcontroller vendors to
program or debug the microcontroller.
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Figure 5: Typical Microcontroller
Various microcontroller options were considered as well as there are numerous
manufacturers. Ultimately the cost, form factor and ease of programming are the
criteria that would determine the choice.
3.5 Power
The Quadcopter needed a sustainable and portable power source to power the
control unit and the motors. Different types of rechargeable batteries were researched
and a number of chemical compositions were taken into consideration. Nickel Cadmium
(NiCd), Nickel Metal Hydride (NiMH), and Lithium Polymer (LiPo) cells are currently the
most commonly used, but each needs to be charged, discharged, and stored differently.
On top of that, each model may require a different cell count or battery configuration as
well.
Nickel Cadmium or NiCd batteries are less common now but they are cheap.
These batteries have cons as well however. NiCd batteries need to be fully discharged
after each use as failure to do so would mean that for future discharge cycles, they will
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not discharge to their full potential. NiCd batteries also have a low energy density – the
capacity per weight.
Nickel Metal Hydride (NiMH) batteries have numerous advantages over the NiCd
batteries. NiMH cells offer higher energy density and don’t have the same performance
issues attributed to improper discharge practices as NiCd batteries do.
The latest cells are the Lithium Polymer (LiPo) cells. LiPo cells offer higher better
discharge performance as they provide better consistency compared to NiCd and NiMH
cells. LiPo cells also offer a significantly higher capacity for their weight; a cell may have
twice the capacity for half the weight of a similarly performing NiMH cell. Hence, LiPo
cells can achieve higher voltage and energy density. LiPo cells need to be monitored
when being charged however. This is the major deterrent when it comes to adopting
this technology. Overcharging can cause the cells to be potential major fire hazards
given the amount of energy packed into such a small space.
The Lithium Polymer battery was chosen in the end due to the advantages
mentioned above.
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4.0 Hardware Components and ConstructionHardware components were chosen from the alternatives presented in Section
3.0. It was important to bear in mind the weight of each component. There were other
decisions that needed to be made in the process of choosing an individual component.
These decisions were made to ensure compatibility with other component parts. This
will be discussed in each of the sections.
4.1 Frame and Structure
Carbon fibre reinforced plastic (Carbon Fibre for short) rods were used for the
arms of the robot. Carbon Fibre Rods are light and proved to have a higher strength-to-
weight ratio when compared pound- for-pound with the other alternatives. Carbon fibre
also has high tensile strength, low thermal expansion. However, it is relatively expensive
when compared to the other alternatives but the small price discrepancy was almost
negligible looking at the advantages Carbon Fibre provided, especially since it is
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significantly lighter and durable compared to the alternatives mentioned in Section
3.1.2. The sketch in Figure 6 shows the proposed basic frame of the IMR. Aluminum was
chosen for the square base initially as can be seen in Figure 7. The figure shows the
initial structure with the Carbon Fibre rods and aluminum square base. The total weight
of the fibre rods, the aluminum base and the miscellaneous screws and nuts used to
secure the components is 3.2oz.
Figure 6: Sketch of Proposed Structure
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Figure 7: Initial Frame
4.2 Microcontroller
The Arduino Mega was chosen because of its greater
memory, processing power and number of ports. It has 54
digital input/output pins, 14 of which offer Pulse Width
Modulation (PWM) that is required to control the motors, 16
analog inputs that provide a 10bit resolution each, and 4
Serial UARTs. The Arduino Mega is a microcontroller board based on the ATmega1280
microprocessor. It has an operating voltage of 5V, input voltage range from 7V to 12V,
128KB of Flash Memory for storing code, 8KB of SRAM, 4KB of EEPROM and a clock
speed of 16MHz. It was a cheaper alternative to the other options considered. The
microcontroller is widely adopted and hence there is more support for it. There are
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numerous ‘shields’ that can be mounted on to it for added functionality. Examples
include the Aeroquad Shield V1.7 and the WiShield 2.0 that will be discussed in later
sections.
The Arduino Mega can be programmed with the Arduino Software provided free
by the developers. The Arduino Integrated Development Environment (IDE) is written
in Java and made for the Processing programming language. It includes a code editor
with features such as syntax highlighting, brace matching, and automatic indentation,
and is also capable of compiling and uploading programs to the board with a single
click.The IDE also comes with a C/C++ library that can be used to simplify I/O operations.
Arduino programs are written in a language akin to C/C++ and hence it is something that
we are familiar with [13]. The Arduino Mega contributes a weight of 1.5oz to the IMR.
4.3 Flight and Stability
4.3.1 Propeller and Motor Combination Configuration
Brushless DC motors were ultimately chosen to provide thrust power to the IMR.
Brushless DC motors have a higher efficiency of 85% to 90% as opposed to the 75% to
80% efficiency of brushed motors. This results in reduced noise, longer lifetime and
more power. These motors provide superior power-to-weight ratios and are very light.
To pick the right motor model, the propeller was chosen first. The light EPP1045
propeller was chosen as they are widely adopted in other implementations of the
Quadcopter. With this design decision, the matching motor for optimal thrust was
sought and research yielded Table 3 below.
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Table 3: Matching Motors for EPP1045 Propeller
The table shows the comparison of the performance of the propeller with
various motors. The criteria in consideration are cost, weight of the motor, maximum
thrust achieved in pounds and the amount of power drawn per pound at maximum
thrust. After the analysis was done, what it came down to was availability. The only
motor available was the Towerpro 2410-09 Open Base Brushless Motor. The statistics
show that it is a cost effective option and that it is really light at 2.05oz. It could provide
better thrust but it is one of the more power-efficient motors. With a total of four such
motors on the IMR, they will contribute a total weight of 8.2oz. The Amp rating is 13.5A.
The positioning of the motor also contributed to the stability. The closer the
motors are to the centre, the more stable the IMR is. However, this compromises the
manoeuvrability of the IMR as the Quadcopter responds better to change in directions
when the motors are further apart. This increases the signal noise fed into the IMU due
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to increased vibration. Extensive testing was done to determine the perfect distance of
the motors from the centre for the right balance between noise and manoeuvrability.
The propeller/motor configurations also differed. As mentioned in Section 1.1,
there are 2 motors that spin clock-wise and two that spin counter clockwise. The right
propeller had to be mounted on the corresponding motor to achieve this. The motors
were wired to Electronic Speed Controllers (ESCs) in 2 configurations to ensure the
clock-wise and counter clock-wise rotations of the motors. ESCs are discussed in Section
4.3.2.
4.3.2 Electronic Speed Controller (ESC)
Since a Brushless Motor was chosen, an Electric Speed Controller was required. A
brushless motor controller or brushless ESC (Electronic Speed Control) is used to vary
the speed of a brushless motor. These function as an interface between the motor and
the battery. Controlled by the microcontroller, the brushless ESC provides variable
power to the motor allowing proportional speed adjustments. The microcontroller
sends PWM signals with different duty cycles to vary the speed of the motor rotation.
Unlike a brushed motor, power cannot be directly applied to a brushless motor. Instead,
the speed control intelligently powers each phase of a brushless motor in sequence,
causing it to rotate.
The Tower Pro w18A Mag8 Digital Brushless Motor ESC was chosen. This
component has a weight of 0.705oz, an Amp rating of 18A and operates ideally at a
voltage of 6V – 12V. These are considerations that are important to note. The voltage
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information needs to be noted for the purpose of selecting the battery. The the total
weight contributed by the 4 ESCs is 2.8oz. The Amp Rating of 18A indicates the
maximum current that the ESC is able to provide continuously to a motor and it is better
to have an ESC with a higher continuous current rating to ensure that the ESC is able to
handle the power requirements of the motor. The Amp rating 18A is good given the
13.5A rating of Tower Pro Brushless Motor 2410-09 chosen.
4.3.3 Six Degrees of Freedom (DOF)
After much research, two chips from SparkFun were chosen to provide the 6 DOF
for the Inertial Measurement Unit. The first is a 5DOF
IMU combo board that incorporates the IDG500
dual-axis gyroscope and the ADXL335 accelerometer
on one single chip. This board enables the 5 axis of
sensing (Roll, Pitch, X,Y,Z) in less than 1 square inch
and weighs less than 0.07oz. The second board is the dual axis IXZ-500 gyro. This senses
the angular velocity on the X and Z axes. This board thus provides Yaw information and
it complements the first board that provides Roll and Pitch. These two chips can be
mounted onto the Aeroquad Shield. The Aeroquad Shield is a printed circuit boards
(PCB) that was made for the Arduino. It was created to mount the two chips as well as
to interface with the ESC connections. The total weight contributed by this set-up is
0.75oz.
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Figure 8 : Aeroquad Shield
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4.4 Communications
The WiShield 1.0 was the chosen Wi-fi module from Async Labs. This is perfect
for the Arduino-based projects and is a ‘shield’ module that can be directly mounted on
the Arduino Mega. This shield provides 802.11b connectivity and is a direct drop-on
plug-and-play solution. It has a 16Mbit serial flash onboard to store web pages and
other data. This space can also be used for storing sensor type data that can be
downloaded in the future. It supports both infrastructure and ad hoc wireless networks
which can be useful in the testing phase. Further research can be found in Section 6.0.
4.5 Battery
The Lithium Polymer (LiPo) cells were chosen since they clearly provided better
performance compared to the NiCd and NiMH battery types. It is really light and has a
good energy density. This is perfect for the project as more power would be provided
from a battery pack that doesn’t weigh too much. A 11.1V battery was chosen and this
is a good volatage rating recalling that the ESCs has a input voltage range of 6-12V and
the microcontroller has an input voltage of 7V to 12V.
4.5.1 Flight Time and Battery Power Dependancy
Given that the Quadcopter would have its own weight as well as other payloads,
we needed to do an analysis to see how much load a certain battery can provide and
how much time the battery will provide for flight given the pay load. The various
components and the corresponding weight calculated in previous sections have been
tabulated in Table 4. The table indicates the weight of the Quadcopter with its basic
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component parts. This weight will be considered the IMR weight. Anything on top of this
weight will be considered payload. Measurements were taken using a 2100mAh battery
again to see how much payload this configuration can take and to see if it is consistent
with the Table 2 in Section 3.1.1. The graph generated can be seen in Figure 9.
Component Weight(oz)
Base/Frame 4.2
Microcontroller 1.5
EE1045 Propellers and Prop
Savers
1.1
2410-09 Motors 8.2
Motor Mounts 0.6
ESCs 2.8
Bindings and Miscellaneous Parts 0.4
Battery 5.2
Total Weight 24.0
Table 4: Total Weight Calculation
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0 2 4 6 8 10 120
2
4
6
8
10
12
Flying weight vs Battery Life
2100mAh
Flying Weight in Ounces (oz)
Batt
ery
Life
( Min
s)
Figure 9: Graph of Flight Time versus Battery Life
The results above show that with no payload (i.e. 24oz), 19.9 minutes of flight
time can be achieved. The graph was extrapolated to predict the flight time for heavier
payloads but it might not necessarily be realised in reality.
4.6 Design Implementation and Final Structure
Having considered the numerous factors to choose component parts, the
eventual implementation of the design was both mechanical and electrical in nature.
Basic mechanical work was done with regards to the construction of the structure.
Minor cutting of the Carbon Fibre rods and drilling was done. Two acrylic pieces were
added as a final design decision to provide two different levels. The bottom level is used
to store wiring and the battery and the upper level is where the logic unit is situated.
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Minor electrical skills were also required to solder the component parts and wire them.
Figure 10 shows the top level wiring diagram and shows the final design.
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Figure 10: Wiring Diagram for IMR
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Figure 11: Final Design
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5.0 Stability and ManoeuvreThere are obviously many factors that affect the flight of the Quadcopter. The
collaboration of components as previously described is a core factor that determines
whether the Quadcopter can take flight or not; the sections to follow describe ways to
stabilize the Quadcopter when it is in the air as well as the constraints on the system
that will allow us to steer the Quadcopter.
5.1 Filtering Noise
A clean analog signal is almost impossible to get. It is always littered with noise
whether it is from the AC signal from the outlets that add 60Hz noise or mechanical
motors that cause vibrations. This noise usually cannot be completely removed but
needs to be minimized in order to get the data that we need. A Second Order
Complementary Filter was used to remove the noise from the accelerometers and
gyroscopes caused by a variety of sources from electrical to mechanical.
5.1.1 Noise Reduction
To obtain the desired signal, it is theoretically possible to use a filter and isolate
the desired signal. Reality is, it is harder than it sounds. There are many uncontrollable
variables ranging from predictable (such as 60 Hz AC noise) to unpredictable (such as
mechanical vibrations and wind) which may add noise to the system and make it more
difficult to isolate for the desired signal. It is extremely difficult to eliminate all noise
from any given signal. The noise is mixed in with the desired signal and simply applying
a filter may not be able to remove the noise without also potentially removing the
signal. In fact, it is impossible to remove just the noise without attenuating the signal if
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the frequencies overlap or if there are common frequencies. For this reason, the Signal
to Noise Ratio (SNR), the power ratio between the signal and noise, has more value in
noise reducing processes and is more frequently used in practice. For the purposes of
this project, moderately controllable variables such as the weather and wind are
removed by testing in an open space that is indoors with relatively low draft.
Mechanical and electrical noise from the equipment is monitored and removed as much
as possible without distorting the desired signal itself using a Second Order
Complementary Filter.
5.1.2 Second Order Complementary Filter
A complementary filter is a filter with a derivative feedback through the filter.
[14] The order of a filter determines how many components that is required. The high
level design for a second order filter requires two integrals from the inputs to the
output. Therefore, a Second Order Complementary Filter is one with two integrals, with
the value of the output being fed back between the first and second integral. A block
diagram of the Second Order Complementary filter can be seen in Figure 12.
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Figure 12: Second Order Complementary Filter [15]
Theoretically and through experiments, it can be seen that the Second Order
Complementary Filter performs drastically better than a First Order Complementary
Filter and without wasting too much more computation time. It can be seen that a
Second Order Complementary Filter removes the noise from the sensors quite well and
leaves a relatively clean signal as compared to the signal received (refer to Figure 13).
Figure 13: Second Order Complementary Filter [15]
5.2 Feedback Control
As with most control systems, the time it takes for the system to reach Steady
State is of utmost importance and is part of the tradeoffs that must be taken into
consideration. A system must respond in a timely manner. There are many factors that
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may affect the response time but a couple of major factors affecting Transient
Response: Computing/executing speed of system, Communication delay.
Computing speed of system is dependent on the speed of the microcontroller
used, but as processing speed is getting faster and faster, finding a microcontroller that
is fast enough has become less of a problem. Execution at the optimal speed and with
the optimal response is still very important. There are methods used in control
engineering that optimize the speed at which the system reaches steady state.
Communication delay is inevitable with any system. We can only ensure that we allow
enough time for the message to be received before re-sending a signal. Further
considerations will be discussed in Section 6.0 Wireless Communication.
5.2.1 Six Degrees of Freedom (DOF)
The principle is that a rigid body in three dimensional (3D) space has six
independent ways it can move (or six DOF). The movement can either be translational
or rotational about the X, Y, and Z axis or combinations thereof (Figure 14). In flight
terms, the axes are called Roll, Pitch, and Yaw. The Roll is tilt from side to side. The
pitch is the elevation of the front. The yaw is the direction of movement relative to the
desired projection, also referred to as side slip. Constraints are needed for each DOF in
order to restrict or enable movement in 3D space.
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Figure 14: Possible independent movements in 3D space [16]
5.2.2 System Control Theory
To control an object in 3D space that is free to move about, all six DOF must be
monitored for unplanned directional changes and adjusted accordingly. Adjustments
can either be done manually or with an automated control system to ensure the object
is of the correct orientation and angle. Control Systems can be classified in to three
categories: Open Loop, Feed-Forward, and Feedback. [17]
Open Loop Controllers, also referred to as Non-Feedback Controllers, are useful
for systems where the system inputs are directly related to the system outputs and the
desired system state, usually by a mathematical formula. Feed-forward Control Systems
are generally used when the effect of an input or command to the system produces a
predictable output. Feedback Systems (or Closed-Loop Systems) are causal systems that
are mostly used in systems that require adjustments and possibly machine learning. The
output of causal systems depends on the previous output(s) of the system. For
Feedback System, the output is determined by comparing the previous output signal
and the reference signal. [17]
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Figure 15: Types of Control Systems: (a) Open Loop (b) Feed-Forward (c) Closed Loop [18]
As seen in Figure 15, different types of systems will react differently to
disturbances to the system. From the description of the project and from the
descriptions of the types of systems, a Closed Loop Feedback System is the most
suitable for a Quadcopter that must adjust according to the sensors that determine its
orientation and direction. There are two types of Feedback Systems: Positive Feedback
Systems and Negative Feedback Systems. [17]
Positive Feedback Systems are causal systems that amplify any small
disturbances to the system. A small perturbation can cause the system to grow
relatively quickly. This is useful when the output of the system needs to be magnified or
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enhanced. [17] In the case of a Quadcopter, a Positive Feedback Systems would
ultimately magnify any noise present in the system and destabilize the system.
Negative Feedback Systems are also causal systems, but instead of amplifying
any small perturbations they will make up for any discrepancy between the desired
output (according to the input) and the actual output so that the system can reach the
desired output. [17] The output of the system is the signal that is fed back into the
system. The difference between the desired signal and the signal fed back is the
command error and will determine how the system should react. If the desired signal
and the feedback signal match, the command error is zero and the system has reached
the desired state.
Along with how a system will reach a stable state is how quickly a system can
reach that steady state. The time it takes to reach steady state is dependent on the
damping of the system. A system can be described to be underdamped, critically
damped, or overdamped. An underdamped system will overshoot the steady state
value and oscillate about the steady state value before it reaches steady state. The
more underdamped the system, the higher the amplitude and number of the
oscillations. A critically damped system is a system that reaches steady state as quickly
as possible without overshooting the steady state value. An overdamped system will
reach steady state without overshooting the desired value but over a longer span of
time. The dampness of a system is represented by the damping constant, ζ. If 0 < ζ < 1,
the system is considered to be an underdamped system which means the transient
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response is oscillatory. If ζ = 1, the system is described as critically damped and if ζ > 1
the system is overdamped, as seen in Figure 16. [17]
Figure 16: How the damping constant affects the time it takes to reach steady state [19]
Because of the nature of the system for a Quadcopter, manual adjustments are
very difficult as the response must be instantaneous, yet human reaction is only so
quick. Thus, to steer the Quadcopter, we must resort to a mechanical-electrical
solution: Accelerometers and Gyroscopes. These mechanisms will help direct and
control the direction of motion of the Quadcopter by outputting any possibly unwanted
changes to the system.
5.2.3 Proportional, Integral, Derivative Controller
A Proportional, Integral, Derivative (PID) Controller contain three terms
(controllers) that are used to control the gain and thus the overall response time of the
system: Proportional, Integral and Derivative. PIDs calculate the difference between the
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output value and a set desired input value and use it to calculate and control the gain of
the system and maximize the response time. The Proportional Controller determines
the reaction to the current error, the Integral Controller sums the recent errors and
provides a better steady state response, the Derivative Controller enhances transient
response but uses the rate at which the error has been changing and therefore can be
unpredictable and cause a lot of jitters. Together, the three terms are used to control
the gain and response time of the system. The tradeoff for speed is how much the
system will oscillate. For a system like the Quadcopter, too much oscillation is
undesirable so the gains will be set accordingly.
The time domain transfer function can be seen and derived fromFigure 17. The
S-Domain transfer function of a PID is: H(s) = KP + KI/s + KDs = KDs2 + KPs+ KI. Using the S-
domain transfer function, one can determine where the poles and zeros of the system
are. The poles are at the denominator factors and the zeros are at the numerator
factors for a fully factored transfer function. For a system to be stable, all poles must be
in the open left half plane (OLHP). If there are any poles in the open right half plane
(OLHP), the system is considered unstable. Any poles on the imaginary axis is
considered marginally stable (or pure oscillatory). The closer the poles are to the
imaginary axis, the quicker the response, but at the same time the system can become
more oscillatory which is undesirable for a Quadcopter. Over time, it is expected that
the error in the feedback loop approach zero: the steady state of the system with the
current input. [17]
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Figure 17: PID Controller loop [20]
5.2.4 Feedback Control Mechanism: Inertial Measurement Units
Inertial Measurement Units (IMU) are widely used to manoeuvre and control the
direction of moving objects from airplanes to satellites to rockets. It consists of a
combination of accelerometers and gyroscopes. As previously discussed, for a system
such as a Quadcopter, the system would need to constrain all six DOF in order to fully
navigate the Quadcopter predictably. The three accelerometers can be used to
constrain the translational motion along the three independent axes and the gyroscopes
can be used to constrain the rotational motion about each of the three independent
axes.
The accelerometer measures the acceleration relative to the frame and acts as a
motion sensor to determine the direction and orientation of movement. It would firstly
need to be zeroed for a certain plane. That plane would then be the position of rest.
The output of an accelerometer is simply a voltage level that is increased if the
accelerometer is tilted to one direction, or decreased if it is tilted in the other direction.
From the output of the accelerometer, one can determine the angle at which the
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Quadcopter is currently at. With three accelerometers placed perpendicular to each
other, one can determine the angle for each of the axes.
The gyroscope maintains the direction by detecting the change in orientation.
Gyroscopes maintain the orientation using the concepts of conservation of momentum.
The gyroscope continuously spins about an axis. Once the spin is axis is skewed, the
output will tell us how the gyroscope is moved and what must be done in order to
balance it out again. As with the accelerometer, the gyroscope also has to the zeroed to
determine the rate of change at the desired constant value (usually at rest). The
gyroscope would then output a certain voltage level when a change in orientation is
detected and this value can then be used to adjust the orientation accordingly.
Using the one device without the other is simply not sufficient. Both devices
must be used in tandem in order to control both the orientation and direction of
movement of the Quadcopter. PIDs will determine how fast it will reach that steady
state while accelerometers and gyroscopes determine the direction and magnitude of
adjustment required to reach steady state due to the inputs. Both the gyroscopes and
accelerometers can be found in compact forms in an integrated chip the size of a
quarter.
5.2.5 Feedback Control Loop
Now that we have generally described all the desired components that will help
stabilize and manoeuvre the Quadcopter, we can put the components together. A
generic form for a feedback control loop with the controller and sensors is:
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Figure 18: Feedback loop including system, controller and sensor configuration [21]
We can replace the generic controller with our controller of choice: the PID
controller. Similarly, the System is our Quadcopter (consisting of the structure, motors,
propellers, etc.) and our output sensors for the feedback loop are the three
accelerometers and three gyroscopes. Our feedback control loop design for the
Quadcopter can be represented by the block diagram below.
Figure 19: Feedback Control Loop with control components
From Figure 19, one can follow the feedback loop to determine the sequential
output of each component. The difference between the sensor outputs and the
reference signal is determined which is then used by the PID to determine the optimal
input to the Quadcoptor so that the output of the system is as desired (the system
output being the flight orientation and direction). The accelerometer and gyroscope
outputs will then be fed through the filter and the measured command error will be
again calculated. The filter was added after the sensor data and before calculation of
the measured command error so that it can remove the noise from the sensors before
using the signal in any component of the system.
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It should be understood that each control component uses a different controller.
The Quadcopter system as a whole can be split into different subsystems. The PID
values for the Roll control may be different than that of the Pitch, Yaw or Throttle. In
addition to those PID controllers, there are also different PID controllers for the auto-
levelling (or stabilization) of the Quadcopter to try to optimize the response to a
disturbance to the system.
5.2.6 Flight Tuning Using Ziegler-Nichols Rules
Many systems can be easily modelled mathematically and an analytical approach
to determining the values for the PID controller can be used. For systems that are
difficult to model mathematically other approaches such as the Ziegler-Nichols Rule can
be used to obtain an educated estimation for the PID which can later be fine tuned
further. [17]
Type of Controller KP KI KD
P 0.5KCR 0 0
PI 0.45KCR 1.2/PCR 0
PID 0.6 KCR 2/PCR 0.125PCR
Table 5: PID gain using Ziegler-Nichols Tuning Rule [17]
To use the Ziegler-Nichols Rule, one must find the critical gain, KCR, and critical
period, PCR, of the system. To find those two values, one must set KD = 0 and KI = 0 for
the PID Controller transfer function: H(s) = KP + KI/s + KDs. Adjusting only KP, one must
find the value that causes the system to exhibit sustained oscillations. The gain at which
the system exhibits sustained oscillations, is known as the critical gain. Using the
frequency at which the system oscillates, one can find the critical period. Then
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according to Table 1, one can choose the desired values for the PID controller.
According to the Ziegler-Nichols Rules, this PID should exhibit close to optimal response
for the system, with perhaps minor fine tuning around these gain values.
5.3 Flight Configuration and Simulation
5.3.1 Flight Configuration Methods and Tools
There are many variables that must be configured in order to control the
Quadcopter in flight. These variables are stored in EEPROM and read before and
throughout operation. There are two methods of setting these variables: Using the
Serial Monitor or with the aid of AeroQuad Configurator v1.2.
The Serial Monitor is built into the Arduino development environment. It allows
for serial communication between the Arduino board and the user computer via USB.
This communication medium is used to upload programs as well as to debug via print
statements and send and request flight configuration parameters.
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Figure 20: Motor Command outputs (S) during simulation of flight with Serial Monitor
The commands to send and request flight parameters can be found in
SerialTelemetry.pde and SerialCommand.pde, respectively. The commands need to be
entered in the command line of the serial monitor. To send or request a command,
enter the letter corresponding to the command, select send and the values will appear
in the Serial Monitor output screen below it. Refer to Figure 20 for the outputs using
the command ‘S’ which requests the motor commands and various other flight
parameters separated by a comma. In the same manner, one can simulate flight
(without propellers attached for safety reasons) by tilting the Quadcopter and sending
the ‘Q’ command to receive continuous sensor data to monitor the change as the
Quadcopter is being moved Figure 21.
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Figure 21: Sensor Data output (Q) during simulation of flight with Serial Monitor
Alternatively, AeroQuad Configurator is an open source software developed by
AeroQuad to test and adjust flight parameters of the Aeroquad before flight. This
software can also be used to set various parameters that control the flight of the
Quadcopter such as the PIDs, filter time constant, transmitter/receiver sensitivity,
levelling limits, etc. Its Graphical User Interface (GUI) is very straight forward and easy
to understand and use (refer to Figure 22). The values can be entered into the
corresponding box and updated by selecting the Update button at the bottom right
corner.
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Figure 22: AeroQuad Configurator GUI with updatable flight parameters
In a similar manner, values such as the PID outputs, motor speeds, sensor values,
etc. can be plotted and seen in graphical form with the AeroQuad Configurator Figure
23. The continuous time line graph helps one to visually see the oscillations occurring
and the sizes of the oscillations.
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Figure 23: Various sensor outputs with AeroQuad Configurator GUI
There is known to be a few bugs with this tool when it comes to setting these
parameters. Even if it says the parameters have been updated, it may not necessarily
be so. The values should always be double checked with the Serial Monitor before flight
to ensure the values were indeed written to EEPROM.
5.3.2 Pre-Flight Tests
Before the Quadcopter takes flight, there is a list of tests that should be
executed. This is for the safety of everyone involved and everyone in the vicinity of the
Quadcopter while it is flying. It is to ensure that the Quadcopter does not fall out of the
sky and or crash into anyone. This could prevent damaging the Quadcopter as well as
prevent causing any bodily harm to oneself and others.
1. Increase the throttle to a point where all motors are spinning.
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2. Tilt the Quadcopter to the left. The left motor should speed up. The right motor
command should slow down.
3. Tilt the Quadcopter to the right. The right motor should speed up. The left motor
should slow down.
4. Tilt the Quadcopter forward so that the front motor is lower than the back
motor. The front motor should speed up. The rear motor should slow down.
5. Tilt the Quadcopter up (the front motor should be higher than the rear motor).
The rear motor command should increase. The front motor command should
decrease.
6. Rotate the Quadcopter clockwise. The front and rear motor commands should
increase.
7. Rotate the Quadcopter counter-clockwise. The left and right motor commands
should increase in value.
The above Pre-Flight Tests were referenced from http://AeroQuad.info and
modified for the Quadcopter. [22] There are also communication related tests that will
be described further in Section 6.0 Wireless Communication.
5.3.3 Flight Control and Results
As with many projects that rely on a variety of variables and have a large amount
of components that need communicate with each other, this project encountered many
issues during the integration period of the development cycle. This section will discuss
the results and problems encountered for the flight components as well as the approach
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to solve them. Further discussion on integration issues and solutions will be discussed
further in Section 8.0 Integration.
There were many issues that surfaced when the project moved from the
simulation phase to the flight testing phase with all the components working together.
Although the data output, graphs, and reaction time during simulation were desirable
and as expected, when it came to flight testing and getting the Quadcopter to stabilize
on its own in mid air, it proved to be a more difficult task than anticipated.
Because of the propellers and the need for mobility, the flight data during could
not be downloaded while the Quadcopter was in flight. It was expected that with all the
hardware components working simultaneously that some extra fine tuning would be
required for the PIDs, filter bandwidth, receiver sensitivity, as well as determining the
appropriate centre of gravity (CoG). A software compensation was also made for the
motors since the motors may not be able to use the same voltage level to reach the
same speed. All of the above considerations were taken into account during the flight
testing phase.
Along with the meticulous positioning of all the components, as previously
described, light weights were added at the end of the propeller arms as needed during
testing to eliminate the CoG as a potential problem causing the drifting. Enhancements
to the structure midway through the term to minimize the amount of vibrations were
also done to eliminate the idea, as much as possible, that the structure was not rigid
enough. Thereafter, work was done on the assumption that most of the variables that
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can still affect the flight of the Quadcopter lie in the software implementation and
stability modelling.
As seen in video Video\PID_underdamped, the roll and pitch of the Quadcopter
will readjust when it is forced off its equilibrium position. It can also be seen that this
levelling PID combination causes the system to oscillate many times before it reaches its
equilibrium point again. This is a sign that the system is very underdamped.
Similarly, Video\PID_overdamped, it can be seen that the system takes some
time to readjust as it relatively slowly moves back to the equilibrium point. As
previously stated, it is desirable to attain a critically damped system. In practice, it is
very difficult to attain and a 5% overshoot is considered desirable. In Video\
PID_closeToCriticallyDamped, it can be seen that the rate at which it readjusts relative
to the overdamped has visibly increased and the number of oscillations and magnitude
of oscillations has significantly decreased.
The above videos and oscillations were obtained with the following KP values and
KI = 0 and KD = 0 for the Roll and Pitch:
KP Observations3.75 Underdamped
3-4 oscillations before it stabilizes4.75 Close to critically Damped
1-2 small oscillations5.75 Overdamped
Difficult to tip off axis. Resistant to change6.75 Overdamped
Very difficult to tip off axis. Highly resistant to changeTable 6: Values of KP and corresponding qualitative observations for Ziegler-Nichols Rule
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To use Ziegler-Nichols Rules for tuning PIDs, it is known that a sustained
oscillatory state must be found. The Roll and Pitch PIDs were programmed to have a K P
of 4.75 which has, thus far, the most optimal response. It can be seen in Video\
PID_sustainedOscillation that with a levelling KP of 6 and KI = 0 and KD = 0 (for both the
pitch and roll), one can get the system to exhibit a sustainable oscillatory state.
Therefore, with Ziegler-Nichols Rules, the PID gains that will have the optimal response
should be KP = 3.6, KI = 2.22 and KD = 0.1125 (refer to Table 6: Values of KP and
corresponding qualitative observations for Ziegler-Nichols Rule). The response for this
set of gain values remained relatively oscillatory (Video\PID_ZieglerNichols). Although,
the Ziegler-Nichols Rules does state that fine tuning may be required as the gain values
are only estimates for the optimal gain values.
As the project progressed, the issue with the drift was narrowed down to the
collaboration of PIDs and zeroing the sensors appropriately. The Quadcopter
demonstrates the ability to readjust if it is pushed off the equilibrium state therefore the
sensors are outputting appropriate values to cause this to occur. It was determined that
if the sensors were zeroed at an angle, the accelerometers would take that to be the
zero point and adjust the output accordingly in order to move the system as a whole
back to that angle (if no pitch and no roll were initially applied). Further testing should
be done to ensure proper collaboration between the PIDs and sensor output values.
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6.0 Wireless Communication (Server)
6.1 Communication System Overview
As it is stated in the problem statement, the aim of the project is to control and
manoeuvre a Quadcopter wirelessly over the internet. An overview of the
communication system for the Quadcopter is shown in Figure 24, where a client process
communicates with a Wi-Fi chip on board a microcontroller, via internet.
The internet is used widely around the world and thus one of the advantages of
implementing this design is so that eventually it can be widely used. Different wireless
standards were considered so as to be able to connect the Quadcopter to a wide Local
area network that is configured to access the internet. Some of the standards looked at
include ZigBee and WiFi for wireless personal area networks (WPANs), which are
discussed further in section 6.2 of this report.
The ideal design implements the TCP protocol in the uplink and UDP protocol in
the downlink as shown in Figure 24. TCP is used in the uplink for control commands and
UDP is used in downlink for feedback. This design is choice is verified by examining the
different protocols and their advantages and disadvantages as described in section
6.3.2. However, due to a re-definition of project goals mid-way through the project to
exclude parts of the original goals such as video feedback, the communication system
had to be re-designed to reflect this change. This is discussed in section 6.3.2 and an
updated communication system is shown later in Figure 26 of section 6.3.2 to illustrate
the change in project goals.
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Figure 24: Original Communication System Design
With the standards mentioned above, a number of things had to be looked at,
such as the choice of the WiFi chip to work with the selected Arduino Microcontroller.
Furthermore depending on the type of feedback, appropriate transport protocols were
chosen. The following sections illustrate the different design options explored and the
solutions chosen for the project. Furthermore, the operations of the WiFi Chip as well as
the challenges faced in implementations and the respective solutions are also discussed
in detail.
6.2 Wireless Standards
For our project purposes, an RF transceiver module was needed to communicate
with a remote client process as well as the Arduino Microcontroller so as to control the
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TCP: Control Commands
UDP: Feedback
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Quadcopter. Several RF modules were investigated for different wireless standards, and
some have been detailed in the following sub sections. The solution for the project is
also identified and discussed in the subsequent sub sections.
6.2.1 ZigBee
ZigBee is a wireless mesh networking standard that is based on the IEEE 802.15.4
specification for WPANs. The technology behind ZigBee is simpler and less expensive.
Due to its low cost, the technology can be widely deployed in wireless control and
monitoring applications, for instance home automation. ZigBee is targeted at radio-
frequency (RF) applications that require a low data rate, long battery life, and secure
networking. The low power-usage allows longer life with smaller batteries, and the
mesh networking provides high reliability and larger range [23].
XBee RF transceiver modules are embedded solutions providing wireless end-
point connectivity to devices. These modules use ZigBee networking protocol for fast
point-to-multipoint or peer-to-peer networking. They are designed for high-throughput
applications requiring low latency and predictable communication timing [24].
The XBee chip is ideal for our quad-copter communication purposes and is
designed to work with the Arduino Microcontroller. However, since the client
application accesses the internet, there needs to be a device that connects the XBee
module to a wireless local area network (WLAN), simply because the standards used for
WLANs and XBee’s are different and hence translation is needed [25].
ConnectPort X4 gateway is a router that is capable of connecting an XBee
module with a WLAN; it provides IP Network connectivity to WPANs. This Gateway
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collects data from XBee chips and sends it to client application on a WLAN, using
Ethernet. The Gateway however is very expensive and costs $449.0 separately [25].
One of the goals of the project is to minimize the overall cost of the project and
thus this option was deemed too expensive for our purposes.
6.2.2 Wi-Fi
Wi-Fi is a specification based on IEEE 802.11 standard. Devices configured to run
Wi-Fi can connect to the Internet if they are within range of a wireless network
connected that can access the Internet. Wi-Fi also allows communications directly from
one computer to another without the involvement of an access point. This is otherwise
known as ad-hoc mode of Wi-Fi transmission [26].
WiShield is an RF transceiver that brings Wi-Fi connectivity to the Arduino
platform. This shield was built specifically for the Arduino platform and allows
throughputs of 1Mbps and 2 Mbps. It uses low power and implements ad-hoc as well as
access point Wi-Fi transmission. Furthermore, it has the ability to create secured
networks with different encryption mechanisms [27].
With just a few configuration parameters to set, this device connects directly to
a WLAN. No translations are required in terms of wireless standards and thus no
additional costs were incurred. Due to its low cost, specifications and its ability to
directly connect to a WLAN, this option was deemed the best solution for our project
purposes.
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6.3 WiShield Configurations
As discussed in the section 6.2.2, the Wishield has different configuration
alternatives. Options are available for the type of network, transport protocol and
encryption mechanisms. The following subsections elaborate more on the available
choices and solutions for our project.
6.3.1 Network Type
The WiShield has in-built implementations of wireless area network connectivity
using either access points or ad-hoc networks.
Access Points:
With Access points such as routers, different security encryption mechanisms are
implemented such as Wired Equivalent Privacy (WEP) and W-Fi Protected Access (WPA)
algorithms. Connection to a specific wireless area network requires re-configuring
routers to reserve an IP address specifically for the WiShield. To connect to these access
points, encryption keys have to be specified as part of the WiShield configuration.
Ad-hoc:
Ad-hoc provides direct communication between the WiShield and a remote PC.
Similarly, for security purposes, encryption keys can be specified. Ad-hoc network
provides for easier debugging conditions, as it eliminates an extra variable; that is the
access point.
Therefore, for our development and testing conditions, ad-hoc network was
used. This configuration worked very well in the course of development of the software
for wireless communication.
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6.3.2 TCP vs UDP
The WiShield has two alternatives in terms of transport protocols that can be
implemented. These protocols were provided as independent applications and
therefore only one at a time could be used for communication purposes. The protocol
applications provided in the WiShield are those of UDP and TCP. The following
subsections, elaborate in detail how the protocols work, their advantages,
disadvantages and how they fit in the goals of the project.
TCP:
TCP is the transmission control protocol. TCP provides a communication service
at an intermediate level between an application program and the Internet Protocol (IP).
TCP is connection oriented; it uses the three-way handshake to establish a connection
between two communicating parties as illustrated in Figure 25. The connection
establishment process begins with the client process attempting to connect to the
WiShield by sending a synchronization (SYN) message. The WiShield then replies to this
SYN message with an acknowledgement (ACK) to signify that a connection has been
established and that data transfer can begin. As part of the three-way handshake, the
client then replies by sending an ACK to acknowledge that a connection has been
established.
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Figure 25: TCP three-way handshake
TCP is a reliable stream delivery service that guarantees delivery of a data stream
sent from one host to another without duplication or losing data.
Since the packet transfer is done wirelessly and wireless channels are not
reliable, a technique known as positive acknowledgment with retransmission is used to
guarantee reliability of packet transfers. This fundamental technique requires the
receiver to respond with an acknowledgment message if it receives the data. Each
packet sent by a source has an identifier or a sequence number, and once the packet is
sent, the sender waits for an acknowledgment before sending the next packet. Hence
the packets arrive in order at the receiver side of the communication, guaranteeing
reliability. To account for lost packets, a timeout is set and if this time expires then the
packet is re-transmitted.
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TCP is optimized for accurate delivery rather than timely delivery, and therefore,
TCP sometimes incurs relatively long delays while waiting for out-of-order messages or
retransmissions of lost messages. It is not particularly suitable for real-time applications
such as Video or Voice over IP. [28]
TCP implements the mechanism known as congestion control, which in theory
throttles the sender side if the network is congested. Throttling of the Sender can have
huge negative impacts in terms of real-time applications.
UDP:
With User Datagram Protocol (UDP), computer applications can send messages,
in this case referred to as datagrams, to other hosts on an Internet Protocol (IP) network
without requiring prior handshaking to set up transmission channels or data paths. The
client must explicitly attach IP address and port of destination to each packet. The server
must then extract the IP address and port of the client from the received packet.
Equipped with this information, the server can reply to the appropriate client with the
proper information. [29]
Thus, UDP provides an unreliable service and datagrams may arrive out of order,
appear duplicated, or go missing without notice. UDP assumes that error checking and
correction is either not necessary or performed in the application, avoiding the
overhead of such processing at the network interface level. [30]
UDP is used best in real-time applications such as Voice over IP and Video
Feedback as these applications can tolerate loss of packets rather than huge delays in
the network packets as in the case of TCP. Table 7 shows the advantages and
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disadvantages of UDP and TCP. Based on the comparison, the appropriate transport
protocol was selected for the Quadcopter operations.
Category TCP UDP
Reliability Reliable Unreliable
Connection States Has states Stateless
Congestion control Yes No
Overhead More Less
Table 7: Relevant differences between TCP and UDP
From Table 7, it can be concluded that TCP is best where reliable communication
is needed; in this case for the Quadcopter control commands. UDP is best for real-time
applications that can tolerate packet loss; in this case if video feedback is implemented.
Thus, the ideal way of implementing the design is to use TCP for control commands in
uplink and UDP for feedback in the downlink as shown in Figure 24Figure 24: Original
Communication System Design of section 6.1.
The project goals were re-defined earlier in the course of development of the
project to exclude video feedback. Hence the feedback connection was implemented
using TCP, as seen in Figure 26. Moreover, as discussed in section 6.3.2, the WiShield
only implements one application at a time, either UDP or TCP; this is consistent with the
re-defined project goals.
As a note, for future groups that may undertake a similar project, a separate Wi-
Fi chip will be needed to take care of video feedback; if video feedback is a priority.
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TCP: Control Commands
TCP: Feedback
Figure 26: Re-designed Communication System
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6.4 WiShield Functionality
Figure 27: WiShield Functionality
As described in Figure 27, once the code is loaded into the WiShield, network
parameters such as source IP address, destination IP address, network type as well as
the security type are configured first. Once the parameters have been configured and
verified, the Wishield will attempt to connect to a WLAN using the parameters specified.
If the connection cannot be established, then it will keep on trying to connect. Once the
connection has been established, the connection state updated and the code
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Start
WiShield Network
Configuration
Connect to Network
Handle Connection
Connected ?
Update Connection
Status
YES
NO
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implementation proceeds to invoke a function that handles the connection based on the
Transport protocol selected.
Figure 28: Handling TCP connection
The function Handlle Connection described in Figure 28, begins by opening up a
TCP socket at port 1000; port dedicated for TCP communication on the WiShield. From
there, the TCP connection state enters a wait state, listening on this port for data to be
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Data Valid
?Write to a digital Pin
Send Reply
Update Connection State
NAKACK
Empty buffer
Open TCP Socket
Initialize Connection State
Listen on Port
Data Received? Store data in buffer
Parse data
YESNO
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transmitted from the Client Application to its socket buffer. If the data is received, it
stores this data in the socket buffer. The data was then parsed to determine if it is valid
or corrupted from the wireless transfer. The routine then continues to invoke a function
that runs the motors accordingly. These control functions were implemented in the
code that runs on the Arduino microcontroller. The WiShield communicates with the
Arduino microcontroller through a serial to parallel interface whose operation is
described further in section 6.5. Once the commands have been executed, the WiShield
was programmed to reply to the client application with the previous command
executed. Furthermore, the socket buffer was emptied to allow for new data to be
stored. The connection state was also changed to wait state to indicate that the
WiShield is waiting for a new command from the client application.
6.5 Serial Peripheral Interface
Serial Peripheral Interface also known as SPI bus is a synchronous serial data link
standard that operates in full duplex mode. A full duplex mode is a system in which
parties can communicate bi-directionally simultaneously.
In SPI, devices communicate in master/slave mode where the master device
initiates the data frame and the slave device is the recipient of this data frame. For
communication between the Microcontroller and WiShield, this approach is used [31].
The SPI bus specifies four logic signals:
SCLK — Serial Clock (output from master)
MOSI/SIMO — Master Output, Slave Input (output from master)
MISO/SOMI — Master Input, Slave Output (output from slave)
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SS — Slave Select (active low; output from master)
Figure 29, shows these signals in a single-slave configuration, as in the case of
the Microcontroller-WiShield communication. SCLK is generated by the master and is an
input to all slaves; this case only one slave. MOSI carries data from master to slave.
MISO carries data from slave back to master. A slave device is selected when the master
asserts its SS signal [31].
For example, if the WiShield sends control commands to the microcontroller,
then the WiShield becomes the master which then asserts the SS signal to select the
microcontroller as the slave and the communication proceeds.
Figure 29: SPI bus, single-master single-slave
For the WiShield, Digital pins 10 to 13 are allocated for SPI purposes;
communication with the Arduino microcontroller. These pins are highlighted in Figure
30, which is the schematic of the WiShield RF transceiver module.
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Master Slave
SCLK
MOSI
MISO
SS
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Figure 30: WiShield Schematic [27]
During each SPI clock cycle, a full duplex data transmission occurs in which:
master sends a bit on the MOSI line; slave reads it from the same line
slave sends a bit on the MISO line; master reads it from the same line
Transmissions normally involve two shift registers of some given word size, such
as eight bits, one in the master and one in the slave; they are connected in a ring. Data is
usually shifted out with the most significant bit first, while shifting a new least significant
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bit into the same register. After that register has been shifted out, the master and slave
have exchanged register values [32].
Then each device takes that value and invokes appropriate functions with it,
such as running motor functions in the case of Arduino microcontroller. If there is more
data to exchange, the shift registers are loaded with new data and the process repeats.
With this serial communication process, if the SPI pins are in use, then they
cannot be used for any other purpose. As such, a challenge arose in that digital pins 10
to 13 are also Pulse Width Modulation (PWM) pins required for motor functionality. This
challenge, along with others is described in section 6.6. Solutions to these challenges are
justified in the same section as well.
6.6 Challenges and Solutions
The following section describes the different challenges faced in the duration of
the project, in terms of design and implementation of the wireless communication
interface. The following challenges came up and their respective solutions are outlined
as well.
6.6.1 Debugging
The software development is done using two languages, Arduino language and
Embedded C. Arduino language is used to initialize and run the WiShield where as C
language is used to program the server implementation of the WiShield. The WiShield
presents a major problem when it comes to debugging a program implementation, as
there is no integrated development environment (IDE) that comes with the product. The
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WiShield only comes with a simple compiler that verifies the correctness of syntax.
Figure 31 shows the simple compiler that comes with the WiShield.
As a solution to this problem, a somewhat different approach was used.
Debugging statements were added into the outgoing packets and then verified in the
client application which runs on a remote PC. With this approach, if an execution
reaches a point in the code that needs to be debugged, then at this point comments
were inserted into the outgoing packet. At the client process depending on the
comments displayed, it was possible to know exactly where the execution of the code
reached. This presented us with a direction in which to follow in the process of server
implementation on the WiShield.
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Figure 31: Simple Compiler provided for WiShield
6.6.2 Pin Conflict
The biggest challenge faced in the implementation of the WiFi communication is
Pin conflict. As mentioned in section 6.5, Pins used to interface the Arduino board with
the WiShield, otherwise known as SPI pins were also used as Pulse Width Modulation
(PWM) Pins for motor control. The pins in conflict were digital pins 10 to 13 as indicated
in the schematic provided for the WiShield in Figure 30 of section 6.6. In proper
operation, these pins are used for only one purpose, either SPI communication or Motor
control.
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There may be different ways of solving this problem, but the best solutions
considered by our group are briefly illustrated in this section. A detailed explanation of
the actual integration process is given in section 9.0.
The first solution considered was generation of PWM signals in software. With
these signals, there was no need to use PWM pins to control the motors. Instead, any
digital pin other than the SPI pins could be used for motor control. Hence digital pins 10
to 13 could be used for SPI communication purposes only. This solution is the best
solution; nevertheless because of time constraint on our part, as more effort was put in
quad-copter stability, this implementation was not feasible.
The second solution was to use two microcontrollers. A primary microcontroller
(PM) was used only to run the stability and maneuvering software. A secondary
microcontroller (SM) stacked with a WIShield was used solely for the purpose of Wi-Fi
communication with the remote client application. The PM was then connected to the
SM physically using wires on certain pins. The digital pins 10 to 13 need not be avoided,
as the WiShield did not use the SPI interface to communicate with the SM. This solution
was implemented successfully and the demonstration was recorded and shown on the
poster fair. The complete integration process which uses this implementation is
explained in detail on section 9.0 of this project report.
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7.0 Wireless Communication (Client)A client is an application or a system which requires remote service from another
system, usually a server. The following section describes how the client system
developed satisfies the project’s objectives.
The objective of the client system was to control the quad-copter through a
graphical user interface. The client system is developed in order to provide service to
the user. In the overall communication system the user is referred to as the client since
the user is one that sends requests to Wi-Shield mounted on the Arduino
microcontroller.
7.1 Client Design
Earlier in the winter term, a client script was written in Arduino language and
embedded C. This script was developed concurrently with the server script to establish a
wireless communication between Wi-Shield and a user, in this case a user running on
Fedora 10 operating system. This communication was achieved through an ad-hoc
network between a laptop running Fedora 10 environment and Wi-Shield.
Initially, UDP protocol was implemented in the wireless communication between
the client and the server script. UDP protocol was chosen since live video feedback was
one of the user interface objectives. However, after re-definition of the project goals
mid-way through the year, live video feedback was excluded. Therefore, this exclusion
of live video feedback influenced the change in transport protocol. The client and server
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script which were implemented using UDP needed to be redesigned to employ TCP
protocol.
The following figure illustrates the ideal behaviour of how the client system
should interact with Wi-Shield.
Figure 32: Ideal Layout of Client System in relation with WiShield
User, who is also the client, utilizes the user interface to select which command
the quad-copter should execute. This command is formed into an IP packet and then
sent over the internet to the server which is running the XAMPP services. The server
executes the PHP code and sends the appropriate manoeuvre command to the Wi-
Shield; in turn the Wi-Shield calls the C subroutine which turns the motors accordingly.
After receiving the manoeuvre command, Wi-Shield sends a reply back to the server, in
turn sends the reply back to the client which is displayed through the user interface.
Figure 33: Actual Implementation of Client System in relation with Wi-Shield illustrates
implementation of communication between Wi-Shield and a user, and how the client
system actually interacts with Wi-Shield.
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Figure 33: Actual Implementation of Client System in relation with Wi-Shield
In contrast with the ideal behaviour of the client system described above, user,
in this case, is a system which is running on Fedora 10 platform; and in addition the
system also has locally installed and running XAMPP services. The locally running XAMPP
services on the user system is necessary since during the development phase the web
browser, which embodies the user interface, was not hosted on a server in order to
keep the project cost down and moreover, was not essential to the development phase.
User selects which command the quad-copter should execute through the user
interface. This command is embodied into a packet along with the PHP and HTML code.
The locally running XAMPP services execute the PHP code in the packet and forward the
embedded manoeuvre command to the Wi-Shield over the Ad-Hoc network. Once Wi-
Shield receives the command, it calls respective C subroutine which turns the motors
accordingly. Subsequent to the receiving of the command, Wi-Shield sends a reply back
to the user. The XAMPP services encase the reply with appropriate PHP and HTML code
and display it on the web browser.
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Figure 34: Client Design
Figure 34 illustrates the way the client side communication was designed to
operate. Upon invocation, the client script setups a socket and initializes the connection
by binding a port in the computer. After the connection is setup, it asks the user to input
a move, where the user would like the quad-copter to move to. If the input provided by
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Reply Received?
Setup Socket and Connection
Bind to port in computer
Ask user for the next move
Verify the input
Send user input to Wi-Shield
Wait for Reply
True
False
False
True
April 7th, 2010
the user is valid and within predefined commands then the input is sent to the Wi-Shield
through the setup connection. Afterwards, the client waits until it receives a reply from
the Wi-Shield and then asks the user for another move.
7.2 Client Process
Figure 35 describes process which was developed and followed on the client side
of wireless communications.
Initially, user selects which command to send to the quad-copter through the
web user interface. The selected command is then sent to the client process through
“from User” stream. The client process sends the command to the server via “to
Server” socket. The server with XAMPP services receives the command and processes it.
After processing the server sends a reply through “from Server” socket. Client process
reads the reply and sends it to the user interface via “to User” stream. Once the user
interface receives the reply, it displays the reply to the user through the web interface.
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Figure 35: Client Process
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8.0 User InterfaceUser interface was developed using HTML coding with embedded PHP scripting.
HTML was used to develop the basic structure of the user interface, such as the titles,
buttons and etc. PHP was used to implement the client code developed earlier in the
term.
Figure 36: User Interface
As seen in the following figure, using PHP the layout of the user interface was
successfully divided into menu, header and frame partitions.
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Figure 37: Components of the User Interface
Figure 37 illustrates the components of the user interface and the purpose of the
components. In the “Frame” area, there is an image which shows where the live video
feedback would be visible, if in the future a camera is mounted on the quad-copter.
Moreover, a display box below the image lists all the previous commands sent, if the
user wants to track the movement of the quad-copter since the initial start. Below the
display box are the basic controls of the quad-copter such as left, right, up, down and
hover.
8.1 Software Requirements
All software used to develop the user interface and the client side
communication codes are open source software, in other words free. They were
obtained through the respective official websites.
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8.1.1 Operating System
The client side communication code was developed using the Arduino
Programming environment. However, the client code which
communicates with the Wi-Shield had to be executed in Linux
environment. Therefore, Fedora 10 was used as the operating
system for the client side communications.
Fedora is free open source operating system which is based on a Linux
environment. Release 10 of Fedora was installed and used for the project since it is fairly
new and stable. However, in future newer releases of Fedora can be used, since Fedora
supports backward capability [33].
8.1.2 XAMPP
XAMPP is a tool which allows website designers
and programmers to test their work on their own
computer without any access to the internet. To simplify
the development and testing process, most of the
security features were disabled by default. However,
these security features can be enabled once the website
is on the internet [34].
XAMPP for Linux with version 1.7.3a was installed.
The XAMPP 1.7.3a package contains:
Apache Web Service
PHP Service
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PHP extensions
MYSQL Database
Perl
Server Side Includes (SSI) and etc.
Due to various scripting services, Apache Web service, SQL Database support and
many more functionalities, XAMPP package offers great varieties of functionalities which
will be useful for future scalability of the wireless communication between Wi-Shield
and user interface [34].
Apache Web Server is used as a host server for
websites with static and dynamic content. A locally
installed version of Apache is useful when developing
web applications since the programmer can preview
and debug the code during development phase.
Moreover, Apache also provides server-side programming language support for scripts
including but not limited to Perl and PHP [35].
PHP is a scripting language designed for web
development in order to produce dynamic web pages. This is
achieved by integrating PHP code with HTML code.
Moreover, a server which hosts a website with embedded PHP scripting needs a PHP
processor module in order to execute the PHP code. However, most of the web host
services offer free PHP support on their servers, thus making use of PHP to develop
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website even more cost effective. During development phase, PHP service was enabled
on the client computer [36].
During development and testing phase of the project only the following services
were enabled while using XAMPP:
Apache Web Service
PHP Service
PHP extensions
8.2 Challenges and Solutions
Various challenges were dealt with during the research, development and testing
phase of the client system.
One of the issues stumbled upon was the Wi-Shield connectivity problem. While
developing the primary server and client communication earlier in the development
phase, there seem to be no response from the Wi-Shield to the client even though all
the code seemed to be accurate and properly thought out. There was no network setup
phase that even occurred as intended. The Arduino Programming environment did not
come with any debugger tools which could be used to fix the code. This obstacle was
overcome by the use of Wireshark, which is an open-source network protocol analyzer.
It is used to troubleshoot networks, communications protocol development. Wireshark
achieves this by analyzing the packet traffic through the system, which it is installed on.
With the help of Wireshark, it came to attention that the client was sending “Gratuitous
ARP request”, which is an Address Resolution Protocol request packet where the source
and destination IP are the same. This pointed out the error in the Wi-Shield header file,
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which asked for the wrong IP address as an input. It should have asked for the client IP
address rather than its own IP address [37].
Moreover, another issue developed when integrating User Interface code and
client code developed earlier in the term. Proper manoeuvre code in client code needed
to be called when a specific button was clicked. For example, the client code that sends
the Left command must be called when user clicks on the Left button. Therefore, PHP
code must call the client code, written in C language, each time a direction button is
clicked. However, a C function call made in PHP doesn’t execute when the button is
clicked; it executes when the page loads. This behaviour occurs due to the fact that PHP
is a server side script; in other words, PHP is executed on a server which hosts the
website. In order to get around this problem, PHP form method can be employed. After
clicking on a button, the PHP code fills out a “form” with the C code embedded within
the PHP code and sends it to the server; which executes the PHP code and forwards the
appropriate manoeuvre command to Wi-Shield. For example, if Right button was
clicked, the PHP code for that button with the embedded C code will be sent to the
server as a form entry. Afterwards, the server would execute the PHP code and send
turn Right command to Wi-Shield [38].
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9.0 Software IntegrationThis section discusses the software integration of the Wi-Fi communication
module with the embedded system module that was responsible with stability and
manoeuvring of the Quadcopter.
As discussed in chapter 6.6.2, the solution chosen was to introduce an
independent Secondary Microcontroller (SM). A Primary Microcontroller (PM) was used
solely to run motors and control the motion of the Quadcopter. The SM was used with
the WiShield for Wi-Fi communications purposes only. The WIShield thus does not have
to communicate with the SM through the SPI interface, as the Quadcopter control
software was uploaded onto the PM.
With this configuration, an interface between the two microcontrollers was
needed so that they can communicate and exchange control commands. To do this,
wires were used to physically connect the microcontrollers on some digital pins. Control
commands were sent from the SM to the PM, which then consequently ran the motors
appropriately.
Each wired connection was used to indicate a control command sent from the
client application. With this process, every control command from the client process
requires usage of two pins, one on each microcontroller. Some of the commands used
to run the Quadcopter include start, stop, increase revolutions and decrease
revolutions. An example is provided below to show how the two microcontrollers
communicate when a start command is issued from the client application.
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This example illustrates the course of action that takes place when a start
command is issued. To start up the Quadcopter, the client application issues a command
that is received by the WiShield that is mounted onto the SM. The WiShield process
then turns the voltage on digital pin 5 of the SM to +5V. Digital pin 5 of the SM is
physically connected to digital pin 32 of the PM using wires as shown in Figure 38.
Turning digital pin 5 to +5V forces pin 32 on the PM to change its voltage to +5V.
The WiShield process then waits for 10ms to change the voltage on pin 5 back to
0V. This again forces digital pin 32 back to 0V. The motor control process was
programmed to poll pin 32 once every 2ms; to inspect any change in the voltage of the
pin. Since the voltage on the pin is programmed to remain at +5V for 10ms and the
motor control process takes 2ms on average to run, it provides enough time for the
motor control process to read this command and respond accordingly. For all the
control commands, dedicated pins were used and polled as described in the example
above.
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Figure 38: Pin 5 of SM (with WiShield) connected to digital pin 32 of PM using a wire [39]
The addition of the secondary microcontroller however adds to the overall
weight of the Quadcopter. The overall weight of the copter becomes 1Kg. This does not
present a problem as the motors chosen are capable of lifting up to 2 Kg of weight.
Furthermore, the batteries used, can power both the microcontrollers and provide up to
5 minutes of flight time before they drain. The integration process was implemented
with apparent success and the two microcontrollers communicated as expected.
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10.0 Production Expenses
10.1 Material Costs
ITEM # Unit Price Total NOTE
Tower Pro 2410-09 6 US $6.39
US $187.90
Brushless Motors
Tower Pro Brushless Speed Controller
6 US $9.99 Brushless Speed Controller
TowerPro Alloy Stick Mount for Motors
4 US $2.00Mount for the motors that also
act as heat sinks
Carbon Fibre Tubing 4 US $2.62 750x6mm
Prop Saver with 3mm Bands 1 US $3.99Propeller saver that prevents propeller from breaking free
Rhino 2150mAh Lipoly Pack 2 US $9.69 Rechargeable Battery Pack
Turnigy 2-3 Cell Lipoly Balance/Charger
1 US $5.95 Battery Charger
Arduino MEGA Module 2 $70.40
CAD $309.23
Microcontroller Module
AsyncLabs WiFI Shield 1 $59.78 WiFi Module
Low cost Ultrasonic Range Finder
3 $26.33 Ultrasonic Sensor
EPP1045 Propellors 3 $6.95 CAD $33.50 Counter Rotating Pair Propellers
Gyro Breakout Board - IDG500 Dual 500 degree/sec
1 US $39.95US $133.90
Gyroscope Board
IMU 5 Degrees of Freedom 1 US $74.95Gyroscope Chip to control
stability of UAV
AeroQuad Shield v1.5 1 US $24.95
CAD $62.95
Interface for Gyroscope to microcontroller
Stackable Headers 2 US $ 7.90
Necessary male and female headers to mount the Gyroscope
and microcontroller
Right Angle Headers 1 US $ 1.95
Straight Male Header (9 Pin) 4 US $ 3.00
Female Header (5 Pin) 2 US $ 1.50
Female Header (9 Pin) 2 US $1.90
Arduino Microcontroller Basic Kit
1 $49.99
CAD $66.84
Used in order concurrently develop wireless communication
code
6 Foot USB cable 1 $2.99 Used with the basic kit
Mini Breadborad 1 $4.29 For custom circuit design
18A DC Power Supply 1 $139.99CAD $203.38 Used for preliminary testing of
UAV 3-cell 2200mAh Battery
Pack1 $39.99 Stronger than Rhino 2150mAh.
Used for final testing and
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presentation
Total CAD $999.70
Table 8: List of Materials and Respective Cost
The total prices in the above table include shipping cost and applicable taxes.
The above table specifies the materials purchased in order to construct the
Quadcopter robot with ability of controlling it over the internet. New parts were
required since it is a first year that this project has been worked on. Moreover, higher
performance parts were necessary due to the aerial nature of the project. The cost of
the materials for this project has accumulated up to $999.70 (CAD).
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11.0 Conclusion and Recommendations
11.1 Conclusion
This section will reiterate the problems faced in this project and their proposed
solutions as well as the accomplishments with regards to the problems.
Since the Quadcopter is a new implementation of the Internet Mobile Robot, a
new design of the robot was needed. The Quadcopter needed to be designed and
constructed to meet the project criteria. Research was done on current remote-
controlled Quadcopters to come up with our own design for our implementation of the
Quadcopter. Based on these current models, component parts were researched to meet
the needs of our design. The design consisted of both a mechanical and electrical
elements. The Quadcopter was constructed after the component parts were acquired
from various sources using mechanical and electrical engineering knowledge. This
accomplishment is vital for future groups as the completed prototype will be the
foundation on which further functionality and applications can be developed.
This project also undertook the challenge of implementing a Wi-Fi
communications design on the traditionally remote-controlled Quadcopter. As such, this
is one of the few Quadcopters that use Wi-Fi technology for communications. Much
research was done and the WiShield 1.0 was used to achieve Wi-Fi connectivity to
communicate remotely with the router. A big accomplishment is the understanding of
the documentation for the module and learning how to program it successfully. The
WiShield itself is a new module and it was a challenge to debug as well. These
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challenges were overcome however, with meticulous code reiteration and testing. This
accomplished in the Quadcopter being able to receive commands and reply with simple
feedback.
Since the Quadcopter is flying in 3-D space, a stability mechanism was required
to ensure stability during flight as well as during directional changes. A hardware and
software solution was proposed. The hardware solution consists of using
accelerometers and gyroscopes in tandem as an Inertial Measurement Unit. The
software solution complements the hardware solution by taking the raw data from the
gyroscopes and accelerometers into a filter to stabilize the Quadcopter. Stability was a
major task to accomplish but rigorous testing and debugging proved successful.
With the design decision to adopt a Wi-Fi implementation, there was also a new
task of coming up with a control unit. A solution proposed to tackle this was the
development of a web browser- based GUI. The GUI was designed and implemented.
The implementation is in its preliminary stages as is the design, leaving it open to future
development. Regardless, it is good groundwork to build upon.
With so many software component parts, the integration of the code was also
exigent. Debugging and careful inspection of the code was done to ensure that there
was no mistake in the coding. Numerous bugs were discovered and resolved.
As such, all the problems that motivated this project have been addressed.
Solutions have been provided but these solutions can always be further improved on.
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11.2 Recommendations
The Project has been a great success but as it is a pioneering one, there are a
myriad of possibilities that can be realized by future groups. The next immediate step is
to find a better way of integrating the wireless module with the microcontroller. Also in
the immediate future, perhaps sonar sensors can be incorporated so that the IMR is
able to prevent crashes. Also feasible in the next phase is the addition of video
feedback. The WiShield can perhaps stream the video feed wirelessly back to the router.
This addition will greatly increase the scope of potential applications for the IMR.
Another possible addition to the project would be the development of a smart-phone
application to control the IMR.
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