Unmanned Aerial Vehicle Arab Academy for Science and Technology and Maritime Transport College of Engineering and Technology Department of Computer Engineering UNMANNED AERIAL VEHICLE (UAV) Presented by: Alexander Mohamed Osman Riyad Ahmed El-laithy Ruyyan Ahmed El-laithy Peter Raouf Zaky Supervised by: Dr. Ibrahim Imam ((July 2007)) Page 1Unmanned Aerial Vehicle ACKNOWLEDGEMENTS After thanking God the Merciful we would like to send our thanks to the followin g people: Firstly we would like to thank Dr. Ibrahim Imam for proposing the idea of an Unm anned Aerial Vehicle and for accepting us to carry on that project. Secondly we would like to thank Dr. Atallah Hashad for giving us a helping hand whenever we needed one and for providing us with solutions for all the challenge s we faced. We would like to thank Dr. Hassan Ibrahim for providing us with help with the el ectrical problems we faced in our circuits. We would also like to thank Dr. Gamal Selim for his encouragement, assistance an d understanding. We would like to thank Dr. Yasser Galal for answering some questions we had abou t DC motors. We would also like to thank Eng. Ahmed Akl, Eng. Renad Kamal, Muhab Bahgat, Ruyh an El-Laithy, Fady Mounier, Beshoy Helmy, Todd Elliot, and Sparkfun Electronics for supporting us and/or making this possible. Last but not least we would like to thank our parents & families for their love, support, and understanding. Page 2Unmanned Aerial Vehicle ABSTRACT Gathering information from locations which are inhabitable, hostile, or difficul t to reach is a crucial aspect for learning new information about unmarked terri tories and activities and aids in human technological advancement. This project is concerned with developing an agent for gathering visual information by holdin g a stationary position or pursuing a dynamic target. The agent is a quadrotor V TOL (Vertical Take Off and Landing) aircraft. This agent should have the capabil ity to hover, fly and follow targets. It should receive and transmit data wirele ssly into a base station. It should move through a predefined plan using a GPS r eceiver. It should also balance itself in the air through a gyrometer and an acc elerometer. In addition it would utilize four ultrasonic sensors for obstacle av oidance and an extra one for landing assistance. The agent would also utilize a wireless camera to transmit a bird s eye view to the base station. Page 3Unmanned Aerial Vehicle TABLE OF CONTENTS 1. INTRODUCTION .......................7 2. CONCEPTUAL DESIGN & PHYSICAL ASSEMBLY .. 12 3. ANALYSIS, COMPONENT-LEVEL DESIGN & SELECTION 3.1 Major Components 3.2 PCB Des ign .. 3.2.1 Interface Boards 3.2.1.1 3.2.1.2 3.2.1.3 GPS interface board Accele rometer / Gyrometer interface board RF Interface boards 24-G .. .18 ..18 .......25 ...27 .27 ................28 ............28 29 ...31 3.2.2 Motor Driver 3.2.3 The Brain.. 4. CONTROL 4.1 Introduction 4.2 SPI communication 4.3 Main PIC Implementation 4. 3.1 Pulse Width Modulation (Motors) 4.3.2 ADC Operation 4.3.2.1 Ultrasonic Senso rs 4.3.2.2 Gyrometer 4.3.2.3 Accelerometer 4.4 Secondary PIC Implementation 4.4. 1 GPS System 4.4.2 RF Transceiver 4.5 RC Unit . .. 33 .........33 .35 ................38 ...38 ............43 50 ...52 ..52 ......5 5 .55 .66 ......75 Page 4Unmanned Aerial Vehicle 5. TESTING TROUBLESHOOTING AND REDESIGN 5.1 Testing 5.1.1 LED Testing 5.1.1.1 Ac celerometer Testing 5.1.1.2 Gyrometer Testing 5.1.1.3 SPI Testing 5.1.1.4 RC uni t testing 5.1.2 LCD Testing 5.1.2.1 Ultrasonic testing 5.1.2.2 Accelerometer Tes ting 5.1.2.3 RC unit Testing 5.1.2.4 GPS Testing 5.1.3 RF Testing 5.1.3.1 Ultras onic Testing 5.1.3.2 Gyro Testing 5.1.3.3 RC Unit 5.2 Previous Chassis designs 5 .3 RF Drivers 5.3.1 Laipac RF TX/RX 5.4 Configuration 1 5.5 Configuration 2 5.6 Brain #3 5.7 Correcting Gyro Output . . . . . . . . . . . 78 ..78 ..78 ..78 78 7 9 ..................79 ..80 ..81 ..81 ................82 .83 .83 83 83 85 ...88 .....90 ...90 ......92 ..96 .....99 100 6. FUTURE IMPLEMENTATIONS ..102 7. CONCLUSION .......103 Page 5Unmanned Aerial Vehicle APPENDIX A : COMPONENT DATABASE AND CHARACTERISTICS . .104 APPENDIX B : CONTROL CODE . 106 APPENDIX C : WEIGHT & THRUST CHARTS .. . 165 APPENDIX D : LITHIUM POLYMER BATTERY CARE .167 APPENDIX E : ICSP PROGRAMMING .169 APPENDIX F : REFERENCES .170 APPENDIX G : BIBLIOGRAPHY ..173 Page 6Unmanned Aerial Vehicle INTRODUCTION The rapid development of micro-processor technology and the continuous growth of integration density of electronical and mechatronical components yields a signi ficant cost reduction of high tech products. Driven by this development it becom es feasible to embed information processing and communicating devices in all sor ts of appliances, toys, production facilities, communication systems, traffic an d transport systems etc. With this integration and the aid of global positioning systems, there has been a surge of development in Unmanned Vehicles (UV). The main benefits of UV s are that they do not require human control and thus can be reduced in size and cost. They also limit human error in several aspects, and reduce if not eliminate hum an endangerment. Unmanned vehicles are developed for use in air, over land and u nder water by both private and government agencies. Several unmanned systems exi st such as Autonomous Underwater Vehicles (AUV), Unmanned Ground Vehicle (UGV), and Unmanned Combat Vehicles (UCV). NASA deploys USVs (Unmanned Space Vehicles) on rock gathering missions from the Moon and Mars. The military advanced UAVs an d renamed them to UAVS (Unmanned Aerial Vehicle Systems) and are used in flight combat. Government search and rescue departments find the UAVs helpful in inhabitable or hazardous terrain such as earthquakes, floods or volcanoes, where no human live s have to be risked. Institutions which have onsite geologists use UAVs for unco vering terrain and rock identification, without having to deploy a whole crew wo rking outside. Departments of transportation can use this device to cover footag e of inaccessible situations such as dead-lock traffic jams or multiple car-cras hes. Government law enforcement and intelligence agencies can specifically find this device useful for reconnaissance and target pursuance, where the UAV provid es the advantages of cheap costs, stealth and a diminished human risk factor. The Unmanned Aerial Vehicle project has been an ongoing attempt to produce a rel iable autonomous hovering or flying vehicle. The project designed and implemente d a four-rotor hovering aerial vehicle. The advantages of a hovering vehicle ove r a fixed-wing Page 7Unmanned Aerial Vehicle flying vehicle include less complexity in design, minimal space for take-off and landing (vertical take-off and landing (VTOL)), indoor flight, maneuverability in obstacle heavy environments and of course the eye-catching ability of being a ble to maintain a static position in mid-air. The advantage of quadrotors over helicopters is that they do not require mechani cal linkages to vary rotor angle of attack as they spin, this simplifies design and control. The use of four rotors allows each individual rotor to have a small er diameter than the equivalent helicopter rotor, for a given vehicle size, allo wing them to store less kinetic energy during flight. These smaller propellers r educe the damage caused should the rotors hit any objects, this also makes the v ehicles safer to interact with in close proximity. The first RC application of a 4-rotor vehicle was the Roswell Flyer made by Area 51 technologies. Now there are several commercially available quadrotor aerial v ehicles, to list a few, Atair aerospace quadcopter , Hammacher Schlemmer four ro tor UFO , Keyence Engager and gyrosaucer and the DraganFlyer V Ti . The team s d esign was inspired by the DraganFlyer V, made by Draganfly Innovations Inc. wher e the four motors and props are laid at the ends of an X Chassis, and in the cen ter lay the majority of the circuit boards and microprocessor dubbed by DraganFl yer Inc. as The Brain . (See figure below) Page 8Unmanned Aerial Vehicle System Block Diagram A general control scheme can be seen in the diagram above. The controller block is composed of two communicating MCU s (MicroController Units). The main MCU doe s most of the calculations and decision making. The main MCU also receives input s from the proximity sensors and stability sensors, while the secondary MCU is r esponsible for communicating with a GPS receiver for positioning and an RF modul e for wireless communication. Both MCU s then drive the outputs for the four mot ors together. The stability sensors block consists of a 3-axis Gyrometer for angular velocity measurement and a 3-axis accelerometer for measuring acceleration. The proximity sensors block consists of 5 ultrasonic sensors placed around the vehicle and un der it, for obstacle avoidance and assisted landing. The GPS receiver block consists of a GPS module that provides position, velocity , heading and altitude readings. The RF transceiver block consists of a 2.4GHz R F Module that communicates bi-directionally with a remote control unit for sendi ng and receiving data. Page 9Unmanned Aerial Vehicle The Motor block consists of 4 high powered brushed motors with a gear ratio of 5 .33:1 and 10x4.5 propellers. Both of these features provide a high thrust vehicl e (As opposed to high speed). These motors are controlled through switching tran sistor circuits using PWM (Pulse Width Modulation). The UAV works in three different modes, in the simplest mode a land based PC sen ds out signals through an RF transceiver in order to steer the UAV in different directions. In the second mode a land based PC receives images from an onboard c amera, then a pattern recognition system identifies a target object and sends si gnals to the UAV through the RF transceiver to steer it toward the desired objec t. If the object is not found the UAV rises in altitude quickly in order to find the object and re-track it. The third mode uses an onboard GPS that gives the c urrent position of the UAV and it compares that to its target destination, and s teers to its target destination then comes back to its initial point. In all mod es an accelerometer and gyrometer are used to provide stability, and ultrasonic sensors are used to measure height and avoid obstacles and in turn to steer the UAV away from them. Because of the ambitious nature of the project, the team decided to build the UA V from ground up. Development of our 4-rotor vehicle can be divided into four ma jor branches. 1. Conceptual Design and Physical Assembly. 2. Analysis, component-level design & selection. 3. Control. 4. Testing, Troubleshooting & Redesign. Although these four stages overlapped and interfered with one another they can b e discussed independently, without much referencing to other sections. Page 10Unmanned Aerial Vehicle CONCEPTUAL DESIGN & PHYSICAL ASSEMBLY The conceptual design as stated previously was inspired by the DraganFlyer, and the team s first step was to identify the design goals. These were the fundament al requirements the team decided upon: 1. Ability to hover, in the sense of generating enough thrust and have enough co ntrol in order to maintain a mid-air static position. 2. Maneuverability in all directions of a three-dimensional plane. 3. Sufficient endurance of no less than 10-15 minutes. 4. A very light-weight body, including a battery with the highes t power to weight ratio we could find since the battery is the heaviest single c omponent of the vehicle. 5. High residual thrust to hover thrust ratio, an acrob atic vehicle was desirable for ability to demonstrate controllability and to per form difficult flight maneuvers. 6. Minimal size & complexity. The team decided to stick very close to traditional designs of 4-rotor vehicles, where four electric motors are placed on the corners of a rectangle, and drive four counter-rotating propellers. These propellers would produce sufficient thru st for take-off, and according to their different allocated power distributed on the four motors would provide maneuverability. Any propeller spinning produces a torque on the body it is attached to. For stability in flight the total result ing differential torque on the body should be zero. This is demonstrated very cl early in helicopters. The main rotor on the roof of the helicopter produces a la rge yaw torque on the body which is countered by the tail rotor on the rear of t he plane. Assuming the main rotor is on a constant rpm, the difference in power to the rear propeller moves the helicopter around the z-axis. Page 11Unmanned Aerial Vehicle The proper rotation of the propellers, goes such as any two adjacent propellers rotate in opposite directions, and any two diagonal propellers rotate in the sam e direction. The sum of rotations of any two diagonal propellers should equal th e sum of the remaining two diagonal propellers. This makes the total differentia l torque on the body about the zaxis zero. The figure below demonstrates the pro p rotation direction. At hover mode, all four propellers would be producing the same amount of torque resulting in zero-net force on the vehicle about any-axis once gravity is taken into account. To make the vehicle increase or decrease in altitude, the speed on all four propellers are increased or decreased respectively. In order to move t he vehicle in any direction of the x or y axis, two propellers adjacent propelle rs are increased in thrust, this causes the vehicle to pitch or roll in the desi red direction, since the sum of the any two diagonal rotors is still the same as their other diagonal pair, this prevents the vehicle from yawing in any directi on other than the desired course. Assuming the vehicle is in hover mode the foll owing table yields a summary of the vehicle control scheme. Use the previous fig ure for propeller reference. Page 12Unmanned Aerial Vehicle Propeller 1 Z+ (Up) Z- (Down) X+ (Left) X- (Right) Y+ (Forward) Y- (Backward) + + 0 + 0 + 0 + + 0 Propeller 2 + 0 + 0 + Propeller 3 + + 0 0 + Propeller 4 As stated earlier, a lightweight body was a must in order to achieve maximum thr ust for ease of flight and acrobatic maneuvers. For the chassis of the plane car bon-fiber was used, a very stiff and lightweight material, with a variety of pra ctical uses commonly used in racecars and RC planes for their unique characteris tics. To save even more weight we used the X-chassis design, where four motors w ould be placed on every end of the Xchassis. This would also give a better chanc e for the high pressure to accumulate and increase under the blade of the propel lers to give higher lift than in a rectangular design. It would also reduce the overall air resistance. The arms of the X-chassis were made from hollow carbon-f iber tubes, and at the end of the tubes the motor mounts were placed. They were welded together using a common adhesive known to the RC world as Epoxy . On the bottom of the X-chassis the battery was mounted, keeping the battery on a lower point would lower the center of gravity of the vehicle giving the vehicle smoother pitching and rolling. On the four battery sides four ultrasonic sensor s would be placed for obstacle avoidance. On the bottom of the battery the fifth ultrasonic sensor was placed to determine height, along with the wireless camer a placed for surveillance purposes, video or image capturing. On the top of the X-chassis the UAV brain board was placed. It carries the accel erometer, gyrometer, RF Transceiver, GPS, motor controllers, ultrasonic sensors connections, and of course the Microcontrollers. The following figure below disp lays the chassis. Page 13Unmanned Aerial Vehicle After going through the design and experimentation of three different prototypes (found in 5.2 Previous Chassis designs). One of the most difficult tasks for us , that absorbed most of our time was coming up with the chassis that can have co mpletely reduced air resistance, maximized technical output power when compared to theoretical power of the DC Brushed Motors involved, uniform density, and as extremely lightweight as possible with all the components that we have had to ad d on the UAV. The net weight on the UAV including all added components added up 990g when measured on the scale, which is almost 1 Kg. The theoretical output po wer given to us by the DC Brushed Motors added to up to a maximum thrust of 390 grams per motor. (See APPENDIX C) Since we have 4 motors on the UAV, the complet e output power given by those motors is 1560 grams (1.56Kg). Technically, the te am managed to output only around 350 grams per motor, adding up to 1400 grams (1 .40Kg) of thrust. The efficiency of our design brought us 89.74% of that power. The loss in power comes up to 10.26% due to friction forces, and minimized air r esistance. It is made mostly out of lightweight Carbon Fiber and Balsa Wood for the base of the electrical circuit. The total weight of the chassis without all the components comes to 43 grams. A CAD model was designed, shown in the followi ng figures. An isometric view is shown below, and the dimensions of the chassis design are shown in the next few pages. Page 14Unmanned Aerial Vehicle Top View: Front View: Right Side View: Page 15Unmanned Aerial Vehicle Calculations: Motor Force: Max OutputTheoretical/Ideal Max OutputTechnical = 390 grams/Motor = 350 grams/Motor Therefore, the Total Motor Output of 4 Motors at Full Power: Max Output4Motors M aximum Payload = 1400 grams/4 Motors = 1400 990 = 410 grams Hence, Max Output in Newtons = 1400 x 9.807 = 13.730 Newtons Max Output per Moto r = 13.730/4 = 3.432 Newtons Net Force: Therefore, Lift of Chassis at Full Power and when Differential Torque = 0. Chass is mass = 990 grams = 0.99 Kg Chassis weight = 0.99 Kg x 9.807 m/s2 = 9.709N Lif t = 13.730 9.709 = 4.021 Newtons Acceleration: Net Force = = Lift - Gravity ma mg 13.730 9.709 4.021 0.99a = a acceleration = 1.4(9.807) 0.99(9.807) = (0.41(9.807)) / 0.99 = 4.061m/s2 1.5 : 1 Therefore, the Power to Weight Ratio: Therefore, Lateral Thrust beyond Hover thrust = (4.061m/s2) / (9.807m/s2) = 0.41 41g Page 16Unmanned Aerial Vehicle Torque: = s ; e Acceleration / Distance to Center = 4.061 m/s2 / 0.14m = 29.007 rad/sec2 = mas * radius2 * (angular velocity) = (0.495) x (0.14) 2 (29.007) where (0.99/2 Motors = 0.495 grams, since it takes 2 motors for the UAV to mov front, back, left or right).= 0.2814 Newtons MAX = 4.061 x 0.14 = 0.56854 Newtons A picture of the UAV with complete physical assem bly can be seen below in the following figure. Page 17Unmanned Aerial Vehicle ANALYSIS, COMPONENT-LEVEL DESIGN & SELECTION 3.1 Major Components : The selection of the motors were brushed motors the GWS EPS-350C with a gearing ratio of 5.33:1, which peak out at 8.0V and 8.0A, each of these weigh 63g and ar e projected to deliver 15.37oz (435.73g) of thrust at peak power. Four of these motors are used, with one on each end of the X -chassis. A figure is placed belo w. Counter-rotating propellers were selected as our default propellers, which are a must in any quadrotor plane, because motors do not turn in the same direction. We selected 10*4.5 propellers which are large considered for our motor. Larger p ropellers are more suitable for high thrust application, and smaller rotors are more suitable for high velocity and aerodynamic capabilities. Our choice was the EPP1045 propeller. A figure of the propeller is placed below. Page 18Unmanned Aerial Vehicle Heat syncs were also used to cool down the motors to increase durability and eff iciency as well as to dissipate the heat created by the motors for a longer, mor e durable life. The team selected EHS300 an aluminum, multi-fin heat sync for go od heat dissipation and proper venting respectively. The heat sync has two large fins and 24 smaller fins. A figure of the heat sync is placed below. We needed a battery source that can provide more than 32A continuously, consider ing each motor can consume 8A, the battery of choice was a Lithium-polymer Thund er Power TP8000-2S4P two-cell 7.4V, 8AH battery. It can work continuously at 12C (96A), and can burst at 18C (144A) which is more than sufficient to have all mo tors working at full thrust. With a weight of 320 grams and dimensions of 128*50 *29mm it had a high power to weight ratio and size relative to its competitors. It would also give us about a good 15 minutes of airtime if the UAV is flying at full power. A figure of the battery is placed below. Page 19Unmanned Aerial Vehicle A compatible charger the Astro-flight 109D was selected. Charging rates from 50m A - 8A. Lithium polymer batteries can charge at a maximum of 1C of their rating, so this charger can charge the battery in the fastest possible time which is 1 hour, for quick practical testing. The battery is two cells, any battery with mo re than one cell requires a balancer, so a blinky battery balancer was used whic h balances the cells before, after and during recharge. A wattmeter was also req uired to measure the voltage and current of the battery before and after recharg e. A powerful and bulky power supply is required to continuously deliver such cu rrent to the charger. The astro-flight power supply was used, with an input of 1 10V/220V and an output of 13.5V, it delivers 12.5A. Figures of the charger (top left), blinky battery balancer (top right), wattmeter (bottom left), and power s upply (bottom right) are placed below. Page 20Unmanned Aerial Vehicle The accelerometer used was the triple-axis ADXL-330. Works at 3.3V logic, and co nsumes 0.32mA, it has three outputs for x, y and z axes. Minimum full scale rang e is 3g, and a sensitivity of 300mV/g. The gyrometer used is the IDG-300 which als o works at 3.0V logic and has a full scale range of 500/sec, and consumes 9.5mA, b ut has only two outputs, x and y. Because of this the team had to place two of t hese IC s onboard, to get angular velocity about all three axes. Pictures of the accelerometer and gyrometer are displayed below from left to right. The IMU five degrees of freedom is an IMU (Inertia Measurement Unit) that combin es the IDG300 gyrometer and an ADXL330 accelerometer. This unit measures x and y angular velocity and x, y, z accelerometer outputs, hence the name 5 degrees of freedom . Its advantages over two separate units are firstly that the x and y o utputs of both have identical headings, and you only have one VCC and one GND co nnection. Disadvantages are if this IC for any reason becomes defective you lose two IC s. A figure of this IC is displayed below. Page 21Unmanned Aerial Vehicle Ultrasonic sensors used were the Max sonar LV-EZ1 which work at 5.0V logic and h ave a maximum range of 255in (6.45m), which measures in increments of an inch, t hey have analog, digital and pulse width modulated outputs. It consumes 2mA. Fiv e of these are placed onboard, four facing x and y axes, in order to detect obst acles around the vehicle, and one on the bottom of the battery facing downwards to detect height and aid in landing. We could not rely on the altitude reading o f the GPS system for height because there is an error tolerance of 5m, this could result in hazardous landings. The extra ultrasonic sensor on the bottom would vi rtually eliminate that error because its resolution is relatively quite high. For communication with ground, radio frequency IC s are used. The Laipac TRF2.4G transceiver was used. It operates at a high frequency, 2.4GHz. Data rate trans mission can work at either 250kbps or 1Mbps. It works at 3.0V logic consumes 10. 5mA in TX mode and 18.5mA in RX mode. Maximum range is 280m. Each unit can send and receive data interchangeably. One of the transceivers is placed onboard, and the other is connected to a land-based PC, they send and receive data to and fr om each other. Page 22Unmanned Aerial Vehicle For unmanned guidance to different destinations a GPS system, the EM-406 was use d. Readings of latitude, longitude and altitude obtained serially are used to tr iangulate the position of the IC. Power input is rated between 4.5V-6.5V and pow er consumption is 70mA, operating frequency is at 1.58GHz. A figure of the GPS i s placed below. jhnjh For the surveillance system the WS-309AS system was used, the package comes with 1.2GHz camera with a resolution of 628*582 and a horizontal definition of 380 l ines. The camera works at 9.0V, and consumes 85mA. A simple 9V battery operates the camera. The package also comes with a receiver with audio out and video out. Linear transmission distance ranges from 50m-100m. A picture of the camera and components are placed below. Page 23Unmanned Aerial Vehicle The selected PIC programmer was the Olimex PIC-MCP-USB programmer. It is a low c ost PICSTART alternative, is MPLAB compatible and thus does not require a RS232 port. In addition it has an ICSP (In Circuit Serial Programming) connector (ICSP programming explained in APPENDIX E). A figure of the programmer is displayed b elow. Page 24Unmanned Aerial Vehicle 3.2 PCB Design Required components for designing and etching a PCB are acetone, a laser printer , glossy paper, a clothing iron, acid and a steel sponge. Firstly the surface of t he brass board is scrubbed with a steel sponge to remove any impurities and any oxidized brass. It is then cleaned thoroughly with cotton drained in acetone. Th e team used the circuit designing program called EAGLE 4.16r1 . Any circuit is p rinted on glossy paper, the printed glossy paper is then well folded around the board to prevent any slip during ironing, then ironed on the brass board. Ironin g continues until the circuit becomes visible from the other side of the printed glossy paper, or preferably when the white paper takes a yellowish/brownish col or indicating a slight burn. (Caution should be taken during ironing, if the bra ss board becomes too hot, the brass actually deforms). After ironing, the paper should be removed leaving the toner ink on the brass board. The brass board is t hen placed in the acid and left until all brass surrounding the printed circuit is dissolved. After removing from acid and rinsing in water, a steel sponge is g ently scrubbed on the toner ink to leave the brass trace under the toner ink whi le removing the ink. Holes are drilled into the circuit board in the appropriate places where components are to be placed. After drilling is complete, component s are welded onto the board using solder and a soldering iron. All circuits used for this project were designed in this manner. Pictures below (left to right) d isplay this procedure. Before these boards were actually designed they were test ed on bread boards first in order to assure everything is working in order, beca use making an incorrect PCB means much wasted time and raw materials. More of th is can be referenced in Section 7, Testing troubleshooting and redesign. Page 25Unmanned Aerial Vehicle Page 26Unmanned Aerial Vehicle 3.2.1 Interface Boards Learning from previous errors we found it would be more convenient to create int erface boards for individual IC s rather than integrate them into one large circ uit. (Much the way a desktop motherboard uses PCI cards instead of making one la rge board.) This is because if any errors occur in the design, or redesigning is desired, the individual IC s wouldn t need to be removed. Frequently exposing I C s to strong heat when welding can damage these components. 3.2.1.1 GPS Interface Board In his board the GPS cable is welded onto the left row of pins. The descending o rder of these pins is; not used, GND, TX, RX, VIN, & GND, again. The first pin i s ignored. The second and last pins (both GND) connect to the right side second pin. The third pin TX connects to the fourth pin on the right. The 4th pin on th e left is RX that connects to the third pin on the right. Page 27Unmanned Aerial Vehicle 3.2.1.2 Accelerometer / Gyrometer Interface Board This follows the same method as the GPS interface board. The E$1 row is the yaw gyro, E$2 row is the roll/pitch gyro. E$3 row is the three axis accelerometer. E $4 row is the pin headers that connect onto the main board. 3.2.1.3 RF boards The TRW-24G is a very sensitive component therefore we designed this interface b oard with a TRW-24G socket for plug and play action onto the board. Page 28Unmanned Aerial Vehicle 3.2.2 Motor Drivers : Designing a suitable motor controller circuit was a challenging task, especially due to the lack of components here in Egypt. The controlled motors could take u p to 64 Ampere bursts for a startup current and up to 8 Amperes as a continuous current. In order to achieve maximum power we needed to cause a minimal voltage drop in our circuit. We came up with the following design objectives: - Switching speed of up to 2KHz (for PWM control) - Minimum Vce drop possible fo r more powerful motors - High current Ic - Low current Ib Unfortunately the tran sistors fitting this description could not be found here in Egypt, but we found a transistor 2SD1062. It is capable of running a current of up to 15A and Vce of as low as 0.3V, but it needed a larger current for Ib than a PIC could provide, therefore we added a TIP120 transistor as an interface between the PIC and the 2SD1062. Since Vce of the 2SD1062 was a function of the Ic current we put 2 tran sistors in parallel to drop the Vce as low as possible while at the same time as suring that it has enough capacity to pass through the required current for the motor. A main feature of this circuit is the PC817 optocoupler, an IC that interfaces b etween the PIC circuit and the motor circuit. Isolating these circuits was neces sary because combining high current components with low current ones can damage the low current components. The optocoupler in the following diagram is labeled as 2. The left side of the optocoupler is connected to the PIC circuit and the r ight side is connected to the motor circuit. The first rows of pins in order are GND (PIC circuit), Vcc (PIC circuit), GND (Motor circuit) and Vcc (Motor circui t). Vcc from PIC (PWM output) circuit goes through a 1.5K resistor through optoc ouplers where the phototransistor is activated and returns to the PIC ground. Th e signal in turn goes through the base of the TIP120 turning it on. The emitter of the TIP120 connects to the base of the 2SD1062 transistors, whose collectors are Page 29Unmanned Aerial Vehicle connected to the motor and the motor is connected to the Li-Poly battery. A circ uit schematic is shown below. Resistors were placed to produce desired voltage d rops. In the final motor driver design, the optocoupler was removed from the motor dri ver and put on the main brain. This was done in order to have smaller motor driv ers, and to have less connections between the main board and the motor driver. A lso large motor drivers facing upwards would make contact with revolving propell ers, and if facing downwards could cause noise with the ultrasonic sensors. Page 30Unmanned Aerial Vehicle 3.2.3 The Brain To avoid the mistakes that occurred in Configuration 2 mentioned in the Testing, Troubleshooting & redesign section the team changed two things mainly. FirstlyTo avoid the problem of circuit design or re-altering, it was decided that the IC s would be mounted on separate boards that would mount on the main Brain board, much the way PCI slots are mounted on a normal PC. In our previous design, shoul d any circuit design errors occur, a new board would have to be made, and all co mponents would have to be welded off the old board, and re-welded to the new bra in. This takes a lot of time, and it is also potentially damaging to the compone nts to be frequently exposed to the welder. Secondly as for having the problem o f high power rated components alongside low power rated ones in one circuit, opt ocouplers were used to interface between the Brain board and motor drivers, this is more thoroughly explained in the previous section 4.6 Motor Drivers . Page 31Unmanned Aerial Vehicle This Main board was designed to accommodate two PIC16LF777s, 4 Motor controller boards connected through 4 opto-couplers, a 3-axis accelerometer, 2 dual-axis gy rometers, 5 ultrasonic sensors, a GPS receiver and a RF transceiver. To keep the circuit as small as possible we used the internal 8MHz oscillators available in PIC16LF777 PICs instead of adding more components to the circuit in the form of crystals and capacitors. The circuit is powered by a 9V battery and has a 5V re gulator as well as a 3V regulator for all 5V Logic components as well as the 3V Logic components to operate. We also added some LEDs to simplify debugging. Late r on we manually welded on some wires to two ICSP connectors to program the two PICs without removing them from the circuit. (As seen in the previous picture). Page 32Unmanned Aerial Vehicle CONTROL 4.1 Introduction The Main PIC is responsible for reading and calculating the orientation of the p lane, and accordingly take a decision. The Main PIC has only 3 PWM modules, ther efore we use an extra PWM from the Secondary PIC. The Main PIC sends commands to the Secondary PIC to increase or decrease the power of one PWM output, it also sends the orientation data to be sent through the RF to the base computer statio n. The Secondary PIC takes the GPS messages and extracts the required values and sends them to the Main PIC, as well as through the RF to the base station. Rega rding the control scheme, there are four separate operation modes: 1. Hover Mode 2. RC Mode 3. GPS Mode 4. Tracking Mode In Hover Mode: Tries to keep the vehicle stable in position. The following pseud ocode demonstrates the operating algorithm. Start up system Read bias values from IMU sensors Loop: Read sensors Calculate A ngles & Height If(HeightRequired Meters ) Decrease PWM if tilted left Tilt right If tilted right Tilt left If tilted for wards Tilt backwards If tilted backwards Tilt forwards Repeat loop Page 33Unmanned Aerial Vehicle In RC Mode: The Secondary PIC is the one that receives the RC commands through the RF, then forwards them to the Main PIC to execute. In GPS Mode: The Secondary PIC takes nds it to the Main PIC, base station. The Main d from the GPS from the the GPS messages and extracts the required values and se and it sends all other useful data through the RF to the PIC takes decisions according to its coordinates achieve Secondary PIC.In Tracking Mode: The base station receives the Video Feed from the Wireless Cam era on board the vehicle and searches for a blue target in view, if it is not fo und the vehicle will gain altitude and search again. Once a target is found the plane will descend quickly and hover above the target and keep following it. The Secondary PIC receives the commands from the base station through RF and forwar ds the commands to the Main PIC which performs the required actions. Page 34Unmanned Aerial Vehicle 4.2 SPI communication SPI communication enables quick communication between two PIC s. One is set as a Master PIC and the other as a slave. Originally one PIC was intended to be used , but failed. (refer to Testing, Troubleshooting & Design : Configuration 2). Th e connection is as follows on the diagram below. The left block represents the M aster PIC and the left block is the slave. A bit is released from the Master SSP SR to SD0, and the slave PIC releases a bit through it s SD0 also. The clocks SC K of both PICS are connected together. When a clock pulse rises and falls from t he master PIC a bit is transferred. Every consecutive clock transfers a bit. Onc e the shift registers reach 8-bits (1 byte) the byte is transferred to the seria l input buffer and the shift register is ready to receive data again. Three conn ections are required, CLK to CLK (C3-C3), Master data out to slave data in (C5 i n to slave data out (C4 C5). C4), and master data Two registers must be set in both PIC s in order to enable this mode; SSPSTAT an d SSPCON. (Actual settings for these registers can be found in APPENDIX B : CONT ROL CODE) Page 35Unmanned Aerial Vehicle SSPSTAT (Status Register) Page 36Unmanned Aerial Vehicle SSPSCON (MSSP Control Register) For desired interrupts bits 6 and 7 of INTCON (Global and peripheral interrupts) should be set. Bit7 of PIE1(SSPIE) should be set. When interrupt occurs bit7 of PIR1(SSPIR) is set. This occurs if either a byte is successfully transferred, a lso in case of collision occurs or overflow occurs. Page 37Unmanned Aerial Vehicle 4.3 Main PIC Implementation Generally as aforementioned, this PIC uses PWM, SPI, and ADC, it decides the orientation and heading of the plane. The following sections divide these tasks and explain each of these elements independently. 4.3.1 Pulse Width Modulation After we have finally tested all our sensors, GPS device and RF devices for corr ect processed data, we can now begin to implement the results as output on the p ropellers through motor control. This is achieved by the use of PWM. In the PIC 16LF777, it has three pins for PWM. The control registers used to enable PWM on this PIC are CCP1CON, CCP2CON, CCP3CON, PR2 and most importantly T2CON, since PW M is controlled by Timer 2 in the microcontroller. These three CCPXCON registers let us enable capture modes, compare modes or PWM. Of course here, we will enab le the PWM. Page 38Unmanned Aerial Vehicle Bit 7: Unimplemented. Bit 6: Unimplemented. Bit 5: Should be set as 0. Second Le ast Significant bit in PWM mode. (10-bit Resolution). Bit 4: Should be set as 0. First Least Significant bit in PWM mode. (10-bit Resolution). Bit 3: Should be set as 1. (To enable PWM mode). Bit 2: Should be set as 1. (To enable PWM mode). Bit 1: Don t care in PWM. (To enable PWM mode). Bit 0: Don t care in PWM. (To e nable PWM mode). The CCPXCON registers will be all set as following: CCP1CON: CCP2CON: CCP3CON: 0 x0F = 0x0F = 0x0F = 0b00001111; 0b00001111; 0b00001111; Page 39Unmanned Aerial Vehicle After setting the CCPXCON registers, we must now set the T2CON register where mo st importantly we must enable TIMER2 of the microcontroller and then set the per iod we need to control our DC Brushed Motors in an optimum way using the PR2 reg ister and setting it with a fixed value. By means of research and supervision, i t was decided to control our motors at a frequency of 750Hz (750 times per secon d). For T2CON, we place the following settings: After setting the CCPXCON registers, we need to now set the T2CON register which enables TIMER2 in the microcontroller that will then control over the frequency or period we need on the Pulse Width Modulation. In order do this we must set t he following bits as follows. Bit 7: Bit 6: Bit 5: Bit 4: Bit 3: Bit 2: Bit 1: Bit 0: Unimplemented. Should be set as 0. (Postscaling will not be needed). Should be s et as 0. (Postscaling will not be needed). Should be set as 0. (Postscaling will not be needed). Should be set as 0. (Postscaling will not be needed). Should be set as 1 in order to enable and turn on Timer 2. Should be set as 1. (Since pre scale with a value of 16 is required). Should be set as 1. (Since prescale with a value of 16 is required). Page 40Unmanned Aerial Vehicle Our goal to control our motors at around 750Hz. Now since the microcontroller ca n execute 2 million instructions per second (500 nanoseconds). Speed should be r educed by prescaling. When you prescale your instructions per second over 16 whi ch is our maximum, then we have reduced the frequency to 125 KHz (125000Hz). Thi s is where the PR2 register comes in handy to further reduce frequency to 750Hz. For PR2, we place the following settings: PR2 is an 8-bit register made available in order to control the frequency output needed on the DC Brushed Motors. After using the T2CON register for prescaling to reduce frequency to 125 KHz, PR2 register is used to enter a decimal value th at will control and limit our frequency to 750Hz. The value to be placed in the PR2 register is calculated as follows. We divide the 125000 Hz obtained by 750Hz which is what is needed. 125000/750 = 166.666667. Since the value to be placed in the PR2 register should be an integer value and is an 8-bit register and carr ies no space for a floating point number, 167 should be entered after subtractin g 1 from it. Therefore, PR2 = 166 The equation for PR2 is: round (Fosc / (4 x 16 x Period Required)) - 1 Hence, Fosc = 8 x 10^6 PR2 = round(8 x10^6 / ( 4 x 16 x 750)) - 1 PR2 = round(8 x 10^6/ (48000)) - 1 PR2 = round(166.66666667)) - 1 PR2 = 167 - 1 PR2 = 166 Page 41Unmanned Aerial Vehicle Setting outputs on the Tri-State Buffers on all ports of the Microcontroller: Since the PWM pins are driving the motors they need to be se as output pins. Thi s is done by setting the registers TRISB and TRISC. TRISC = 0x00 Hex TRISB = 0x00 Hex = = 0b00000000. 0b00000000. The diagram of the PIC 16LF777 can be used as a reference below for the output p ins CCP1 on Port C2, CCP2 on Port C1, and CCP3 on Port B5. *NOTE: Please see APPENDIX B for the sample code of Pulse Width Modulation and h ow to control it. Page 42Unmanned Aerial Vehicle 4.3.2 ADC Operation Here using the Analog - to - Digital converters is most crucial in order to auto mate our Unmanned Aerial Vehicle (UAV). For the most part, most or all of our se nsors, ultrasonic, gyrometer and accelerometer give us feedback on our control s ystem. The Ultrasonic provides us with a way for collision detection and obstacl e avoidance. The accelerometer and gyrometer provide us with crucial data to hel p us stabilize our UAV in mid-air and maintain a static hovering position. It ca n also help the UAV to auto-level after traveling in a certain direction, like a co-pilot. The outputs of those sensors are analog voltages. The Analog - to - digital conv erter here helps with converting those outputs into useful data ready to be used and processed by the microcontroller. In this project we use the 16LF777 PIC by Microchip. It contains an abundant 14 channel 10-bit ADC. We have 11 inputs from those sensors. Five alone for the ultrasonic sensors, pla ced on the front, back, left, right, and bottom sides of our UAV for height accu racy. The ultrasonic s range is far as 6.45m (254 inches) and as small as 15cm ( 6 inches) to aid the UAV in landing due to its blind spot. Six channels are used for 2 Gyrometers and an accelerometer. Each gyrometer outputs the rate of angul ar velocity in the X and Y planes, so we need three channels since we have 2 gyr ometers. One input/channel will be ignored from the second gyrometer. The accele rometer needs 3 channels since it measures acceleration in the X, Y, and Z direc tions. This makes a total of 11 channels. Therefore, 3 channels on our 16LF777 m icrocontroller will not be used out of the 14 channels. In order to set this up in our PIC we must enable certain bits in our control re gisters of the 16LF777 microchip. These control registers are the ADCON0, ADCON1 , ADCON2, PIE1, and PIR1 and last but not least the INTCON register to enable ou r interrupts especially when the ADIF (AD Interrupt Flag) is set after every con version in the PIR register. The result of the Analog-to-Digital Converter is pl aced in the ADRES (AD Result) register. It consists of 2 8-bit registers, ADRESL (AD Result LOW) and ADRESH (AD Result HIGH). Page 43Unmanned Aerial Vehicle Page 44Unmanned Aerial Vehicle Page 45Unmanned Aerial Vehicle For ADCON0, we place the following settings: Bit 7: Bit 6: Bit 5: Bit 4: Bit 3: Must be set as 1 since we are using the Internal Oscillator. Must be set as 1 si nce we are using the Internal Oscillator. Analog Channel Select bit. Analog Chan nel Select bit. Analog Channel Select bit. Bit 2: A bit that controls the start of conversion or end of conversio n. Bit 1: Bit 0: Analog Channel Select bit. Turns on the ADC modul e in the microcontroller. Bits 5,4,3,1 are used to select the channels we need to take our inputs from. Th erefore, you need to toggle through them as we read our values over the output i nterval time. We start out by reading through channel 0, then 1, then 2, until w e reach channel 10 (11 Channels) then go back to Channel 0 to take new readings to process for our new interval. Page 46Unmanned Aerial Vehicle For ADCON1, we place the following settings: Bit 7: Must be set as 1 for Right Justification in the ADRES register. In reading our r esult from the ADRES register, we read all the 8 bits from ADRESL and the least significant bits of ADRESH and multiply it by 256. Bit 6: Must be set as 1 since we are using the Internal Oscillator. Bit 5: Bit 4: Must be set as 0 since our Vref+ is normally the VDD of the PIC. Must be set as 0 since our Vref- is normally the VDD of the PIC. Bit 3: Bit 2: Bit 1: Bit 0: Must be set as 0 since we need to enable 11 Channels. Must be set as 1 since we need to enable 11 Channels. Must be set as 0 since we need to enable 11 Channels . Must be set as 0 since we need to enable 11 Channels. The bits 3,2,1,0 of PCFG(X) remain fixed since we are enabling only 11 Channels for the ADC to read from. The pins where pins AN11, AN12 and AN13 of the microco ntroller 16LF777 remain digital I/O pins depending on the settings of the Tri-St ate Buffers for the ports. For ADCON2, we place the following settings: Bit 7: Unimplemented. Bit 6: Unimplemented. Bit 5: Must be set as 1, since we wi sh the conversion to take 12TAD (24 sec). Bit 4: Must be set as 0, since we wish the conversion to take 12TAD (24 sec). Bit 3: Must be set as 1, since we wish t he conversion to take 12TAD (24 sec). Bit 2: Unimplemented. Bit 1: Unimplemented . Bit 0: Unimplemented. Page 47Unmanned Aerial Vehicle The reason why 12TAD is necessary here is simply because one TAD is equivalent t o 2 sec. The acquisition time must not exceed the minimum of 19.72 s which is ho w long the ADC before the ADC starts conversion automatically. Therefore, 2 s * 12 = 24 sec, which is how long the ADC needs to acquire our dat a from one input channel. In order to keep the microcontroller working efficiently and processing data wit hout having it constantly polling and wasting processing power on all kinds of d ata coming in through the Sensors, GPS device or RF transceivers, we use interru pts. Concerning our sensors we set the PIE1 control register in our microcontrol ler. The Analog-to-Digital Interrupt Enable (ADIE) is bit number 6. We set it to 1. Whenever the ADC finishes a conversion, it will set the Analog-to-Digital In terrupt Flag in (ADIF) to 1 in register PIR1, interrupting the PIC. After we tak e our reading for the ADC, we must clear the ADIF in the PIR1 register in our so ftware or else the PIC will keep itself running in a loop. Then we must change o ur channel through the bits 5, 4, 3, and 1 in the ADCON0 register. When this is done, we start a new conversion by the setting the bit number 2 (GO/DONE) as 1 i n the ADCON0 register until the end of conversion is complete and the ADIF is se t again calling the interrupt function in our microcontroller. Setting our inputs on the Tri-State Buffers on all ports of the Microcontroller: Since we have already set our control registers of the ADC module most important ly, we need to set the tri-state buffers on our ports in order to receive our in puts from the sensors. This is done by setting the registers TRISA, TRISB, and T RISE. TRISA = 0xFF Hex TRISB = 0x0E Hex TRISE = 0x07 Hex = = = 0b11111111. 0b00001110. 0b00000111. Page 48Unmanned Aerial Vehicle In the summary of registers shown above, we must be very careful when setting th e TRISE register because only the three least significant bits here control the PORTE Data Direction Bus, unlike TRISA where the complete register is used for o nly 6 pins. If we set the TRISE = 0xFF, it will cause the PIC to set two interru pt flags IBF and OBF and enable PSP Mode , which will cause PORTD to engage in p arallel communication. This will cause the PIC to enter in an infinite loop of i nterrupts and if the flags are not cleared in the software. It almost causes the microcontroller to seem to Halt in a sense. Page 49Unmanned Aerial Vehicle 4.3.2.1 Ultrasonic Sensors The ultrasonic sensors used on the UAV can detect up to 254 inches 6.45 (meters) and the minimum distance it can detect due to its blind spot is 6 inches (15 cm ). The sensor generates a new reading every 49 milliseconds. Since the microcont roller can take readings much faster than the ultrasonic sensor s output, if we take the readings at that speed, it will cause a lot of noise in our program for the UAV, so it is best we take our readings every 49 milliseconds to avoid the noise and make sure we have a new reading every time to be put to good use. Every 0.01 Volts on our Ultrasonic sensor represents 1 inch of distance. Therefo re, if the voltage on the output pin of the ultrasonic sensor is 0.20 Volts, the n the distance it reads is 20 inches, therefore it is very simple to use. In order to le equation Vref N : is nce voltage hich is 10, alent to 50 calculate the distance we need in our PIC 16LF777 we use a very simp which is: Distance (in Hexadecimal) = (Vin/Vref) X (2N) ; where Vin the Voltage input coming from the Ultrasonic Sensor. : is the refere from our circuit which is 3.30V : is the number of bits of the ADC w therefore is 1024 For example, If Vin Vref = = 0.50V (which is equiv inches read). 3.30VThen, 0.50/3.30 X 1024 = 155.1515 Hexadecimal In the ADC of the PIC 16LF777, the ADRES (AD Result) register will read 155 and will truncate the 0.1515. If we take the reading 155 from the ADC and try to convert it back, it will be a s follows: Page 50Unmanned Aerial Vehicle Vin = (Reading from ADRES Register in HEX / 2N) X Vref Vin = (155/1024) X 3.30V = 0.4995 Volts. Therefore the error is: (1 which is quite accurate. (0.4995/0.5) ) X 100 = 0.1 % *NOTE: Please see APPENDIX B for the sample code of the Ultrasonic Sensors. Page 51Unmanned Aerial Vehicle 4.3.2.2 Gyrometer The gyrometer used was the IDG300. This IC gives accurate readings of angular ve locity. All three angles were needed for control of the UAV, on the x, y and z a xes; traditionally in flight labeled as roll, pitch and yaw angles. Angular velo city is measured accurately with a sensitivity of 2 mV/ /s. So every degree of rot ation would indicate 0.002V electronically. The first thing to do was to interpr et the signals into degrees, 0 - 360. This IC operates so that if the IC is rotated suddenly then stopped, you would get a change in reading only when the IC is mov ing, only when there is angular velocity. Thus an adder function is needed to co nstantly integrate the tilt intervally through the selected frequency, as genera l equation is as follows: SUM SUM SUM new t new Where is initially set to 0. is the latest reading from the gyro output and T is the sampling period. After the electric signal would be received on the ADC ports of the PIC it would be multiplied by the following equation to give degrees: AngleNew AngleOld Vin * 1024 t * 3.3 0.62 Also any negative value for tilt had 360 added to it, since simple sin and cos f unctions behave differently to negative values. 4.3.2.3 Accelerometer The accelerometer used was the ADXL330. This gives accurate measures of accelera tion about all three axes. Typical sensitivity of this IC is 300mV/g, so every 1 m/s2 of acceleration would indicate 30.58mV electronically. Primarily this IC ha s two main functions. The first is to indicate the initial angles of x and y in reference to the xy plane perpendicular to the gravity vector, so that the UAV c an take off from any angled surface, if an accelerometer was not used, the syste m would always assume that the plane it was taking off from was always perpendic ular to the vector of gravity, causing flight to be unstable. To use the acceler ometer as an inclinometer, assuming X and Y are the acceleration values obtained from the corresponding axes on the accelerometer then, simply Page 52Unmanned Aerial Vehicle X=sin -1 X g Y Y=sin g -1 The second use is to produce accurate estimations of acceleration, velocity and position, for use in the simulation. A fixed reference point is taken, more accu rately the fixed axes at the point of takeoff. Acceleration and velocity in refe rence to that point are calculated. Distance from that point is calculated, and distance traveled around that point is also calculated. Considering the accelero meter uses the angles supplied from the gyrometer, a traditional 3D rotational m atrix is used to rotate the constantly generated acceleration vectors around the reference axes, so that every value from the accelerometer has a X, Y and Z com ponent on the reference axes. Rotation around the x-axis is defined as : 1 RX( X) = 0 0 cos sin X X 0 sin cos X X where X is the roll angle 0 Rotation around the y-axis is defined as : cos RY( Y) = Y 0 1 0 sin 0 cos Y 0 sin Y where Y Y is the pitch angle Rotation around the z-axis is defined as :cos RZ( Z) = sin 0 Z Z sin cos 0 Z Z 0 0 1 where Z is the pitch angle Multiplying all these matrices together would give the following matrix: Page 53Unmanned Aerial Vehicle cos Y cos Z sin Y sin X cos Z cos sin Y A 1 X X sin sin Z Z cos Y sin Z sin Y sin X sin Z cos sin Y X X cos cos Z Z sin Y sin X cos cos X Y Y cos X cos Z sin cos X sin Z sin cos if X,Y and Z are the acceleration values obtained from the corresponding axes on the accelerometer then, ReferenceX = Xcos Xcos Y + Y(sin Ycos Xsin Z-sin Xcos Z) +Z(sin Ycos Xcos Z+sin Xsin Z) ReferenceY = Xsin Xcos + Y(sin Ysin Xsin Z+cos Xco s Z) + Y Z(sin Ysin Xcos Z-cos Xsin Z) ReferenceZ = - Xsin + Ycos Ysin + Zcos Ycos Y Z Z Integrating with respect to time once gives velocity, and integrating twice give s position. Adder functions are used for velocity and position for each referenc e axes. Another adder function is created taking the absolute value of every acc eleration reading, then multiplying them by time twice in order to calculate the distance traveled. All adder functions for total rigid body acceleration, veloc ity, distance from origin and distance traveled, this simple equation is used. V alue X 2 Y 2 Z2 Page 54Unmanned Aerial Vehicle 4.4 Secondary PIC Implementation Generally as aforementioned, this PIC uses PWM, SPI, USART, and communicates with an RF module. It handles communication tasks for the Main PIC. It also acts as a secondary PWM module. The following sections divide these tasks and explai n each of these elements independently. 4.4.1 GPS System GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, land surveying, commerce, and scientific uses. GPS also provides a p recise time reference used in many applications including scientific study of ea rthquakes, and synchronization of telecommunications networks. There is a conste llation of 30 (earth orbiting satellites as of April 2007) that transmit precise radio signals. Their orbits are set up so that at any given point and time on t he earth s surface there are at least six of these satellites in reach. A figure below demonstrates the constellation of NAVSTAR GPS satellites. Page 55Unmanned Aerial Vehicle A GPS receiver calculates its position by measuring the distance between itself and three or more GPS satellites, using trilateration. Measuring the time delay between transmission and reception of each GPS radio signal gives the distance t o each satellite, since the signal travels at a known speed. The signals also ca rry information about the satellites' location. By determining the position of, and distance to, at least three satellites, the receiver can compute its positio n using trilateration. Receivers typically do not have perfectly accurate clocks and therefore track one or more additional satellites to correct the receiver's clock error. The figures below briefly explain trilateration, where at the center of each sph ere there is a satellite. When two spheres intersect they create lines. When the third sphere intersects it creates a point revealing the location of the receiv er. The coordinates are calculated according to the World Geodetic System WGS84 coor dinate system. Position is determined by latitude and longitude which are basica lly angles, latitude ranges from 0-90 north and south, and longitude ranges from 0-180 west and east. The figures below display latitude and longitude. Page 56Unmanned Aerial Vehicle To calculate its position, a receiver needs to know the precise time. The satell ites are equipped with extremely accurate atomic clocks, and the receiver uses a n internal crystal oscillator-based clock that is continually updated using the signals from the satellites. GPS satellites continuously transmit almanac and ephemeris at 50bps. The almanac consists of coarse time information and orbital data (speed and path). The ephe meris gives the satellites precise orbit. The almanac assists in the acquisition of other satellites. A complete almanac transmission is a 37,500 bit navigation message that takes 12.5 minutes to download. This long delay occurs when a new receiver is first turned on. Each satellite transmits its navigation message wit h at least two distinct spread spectrum codes: the Coarse / Acquisition (C/A) co de, which is freely available to the public, and the Precise (P) code, which is usually encrypted and reserved for military applications. The C/A code is a 1,02 3 bit long pseudo-random code broadcast at 1.023 MHz, repeating every millisecon d. Each satellite sends a distinct C/A code, which allows it to be uniquely iden tified. Page 57Unmanned Aerial Vehicle The receiver identifies each satellite's signal by its distinct C/A code pattern , then measures the time delay for each satellite. To do this, the receiver prod uces an identical C/A sequence using the same seed number as the satellite (two or more systems using matching seeds can generate matching sequences of non-repe ating numbers which can be used to synchronize remote systems). By lining up the two sequences, the receiver can measure the delay and calculate the distance to the satellite, called the pseudorange. The pseudoranges are then the time the s ignal has taken from there to the receiver, multiplied by the speed of light. Th e orbital position data from the Navigation Message is then used to calculate th e satellite's precise position. Knowing the position and the distance of a satel lite indicates that the receiver is located somewhere on the surface of an imagi nary sphere centered on that satellite and whose radius is the distance to it. W hen four satellites are measured simultaneously, the intersection of the four im aginary spheres reveals the location of the receiver. The orbital position data from the Navigation Message is then used to calculate the satellite's precise po sition. Knowing the position and the distance of a satellite indicates that the receiver is located somewhere on the surface of an imaginary sphere centered on that satellite and whose radius is the distance to it. When four satellites are measured simultaneously, the intersections of all four imaginary spheres reveal the location of the receiver. Often, these spheres will overlap slightly instead of meeting at one point. The receiver then moves the overlapping pseudoranges with the same amount (regardles s of distance of receiver to satellite) till an intersection point is created th is point is usually the most probable position. This scenario is shown in the fo llowing figure. Page 58Unmanned Aerial Vehicle An overlapping pseudorange occurs here. Instead of having one intersection point , a room is created by all three points of B . All distances are subtracted by t he same amount, in this case 0.5, in order to receive an intersection point at A . Point A is considered the most probable point of the receiver. Regarding GPS time as opposed to the conventional second, minute and hour; you o nly have seconds, more precisely seconds of the week. In a normal clock when the seconds reach 60 it starts a new minute. In GPS time when the seconds reach 604 ,800 it starts a new week, this is calculated by 7(days)*24(hours)*60(minutes)*6 0(seconds). As for GPS date as opposed to the year, month, and day format of the Julian cale ndar, the GPS date is expressed as a week number and a day-of-week number. The w eek number is transmitted as a ten-bit field, and so it becomes zero again every 1,024 weeks (19.6 years). GPS week zero started at (00:00:19 TAI) on January 6, 1980 and the week number became zero again for the first time at on August 21, 1999. This event is known as a rollover. After a GPS does a full almanac download, GPS systems boot in 3 different modes. Those would be cold start, warm start and hot start. In cold start, time and po sition are known within some limits, the almanac is known and the ephemeris is u nknown. In warm start, time and position are known within some limits, the alman ac is known, and at least three satellite ephemeris are known from the previous operation. In a hot start all ephemeris for all satellites are known so a hot st art occurs. The GPS receiver chooses how to start based on the time between last turn off and current turn on. If this time was a few minutes the GPS chooses ho t start which takes 1 second, if it was a few hours the choice is warm start whi ch takes 38 seconds, anything longer than that produces a cold start which takes 42 seconds. Most GPS systems have two protocols SirF protocol and NMEA protocol. In our case the NMEA protocol was used. NMEA protocol simply contains input messages and ou tput messages. (Refer to the NMEA reference manual) Page 59Unmanned Aerial Vehicle Input messages selected to initialize the GPS are: $PSRF100,1,4800,8,1,0*0E\r\n $PSRF103,04,00,02,01*22\r\n $PSRF105,0*3F\r\n $PSRF is used for input messages. The star means the following two characters are checksum, NMEA checksum operates by 16-bit XOR a checksum calculator code is shown in the APPENDIX B : CONTROL C ODE, and /r/n represent carriage return and line feed, whose HEX code are 0D 0A. All other fields in between them are data fields for different settings. $PSRF1 00,1,4800,8,1,0*0E\r\n This message was used for setting the serial port. 100 in the first field represents serial port settings. 1 in the second field is for N MEA protocol, 4800 is for baud rate, 8 is for 8 data bits, 1 is for 1 stop bit, and 0 is for no parity bit. $PSRF103,04,00,02,01*22\r\n This line is used for en abling and disabling output messages, 103 is used for query/control mode. 04 is used for RMC mode, 02 is used for releasing the message at 2Hz, 01 is used for e nabling checksum. $PSRF105,0*3F\r\n 105 is used for development data. The 0 repr esents debug off should any error occur, so that our PIC does not receive any un necessary input. When a GPS is turned off, it s last settings before being switc hed off will be saved in it s battery powered RAM. When turned on, these setting s resume. These input messages were considered necessary in order to set the ser ial port correctly for USART communication, RMC mode was chosen because this one single message had all the necessary information required. The third message is for turning off debug to avoid unnecessary input to the MCU. A 16-bit XOR CRC creator was necessary to give input messages. A JAVA code is di splayed in the APPENDIX B: CONTROL CODE. Page 60Unmanned Aerial Vehicle Later on a program called SiRF Demo PC GPS Utility v3.83 was found very helpful for obtaining latitude and longitude coordinates for our tested range area. It c an also be used as an initialization alternative. To initialize your GPS time, y ou simply click setup then click GPS Time PC Time as shown in the figure below. Usually the demo starts in SiRF protocol. To switch it to NMEA protocol you simply click action then Swi tch to NMEA Protocol , to open NMEA Setup. In this window as shown in the figure below, you can select each message and it s frequency per second. Highlighting checksum is preferred for message validation. For NMEA, baud rate should be set at 4800bps. After powering off the GPS receiver, GPS time, message type and freq uency are saved. Page 61Unmanned Aerial Vehicle Output messages received from RMC mode (in order) are UTC time, data validity, l atitude, north/south indicator, longitude, west/east indicator, velocity over gr ound in knots, heading measured clockwise from north in degrees, and date A samp le output message is shown below: $GPRMC,161229.487,A,3723.2475,N,12158.3416,W,0 .13,309.62,120507, ,*10 The first two letters following the $ represent the devi ce in use. The GP stands for GPS. There are other devices such as: LC Loran-C TR Transit SATNAV AP Autopilot (magnetic) HC Magnetic heading compass RA Radar SD Depth sounder VW Mechanical speed log Latitude and longitude are displayed in degrees and minutes, At a latitude of 30 N (Cairo, Egypt), the latitude minute = 1847.54m and longitude minute = 1608.1m ( distances change because the circumference of parallel of latitude changes, Eart h is not a cylinder, please refer to http://home.online.no/~sigurdhu/Grid_1deg.h tm ), velocity is multiplied by 1.852 to change from knots to km/hr. Then course heading in degrees ranging from 0360 moving clockwise from north. The final field b efore the checksum is date. The only fields needed were data validity, latitude, longitude, velocity and heading. VTG mode was desired to attain height, but dur ing testing, height in MSL (Mean Sea Level) was quite inaccurate. At a change of height of about 4 meters, the GPS detected a change of height of 10 meters whic h is an error of over 150%. Latitude, longitude velocity and heading are transmi tted via RF to the simulation. Page 62Unmanned Aerial Vehicle A destination in GPS mode is set by pre-inputting a target destination, in the P IC program, in latitude and longitude. The following steps are taken: 1. Y = Target Latitude Present Altitude 2. X = Target longitude Present Latitude 3. Distance = X2 Y2 4. TempAngle is obtained by tan 1 Y X Desired course heading is obtained by the following scheme: Y + + X + + Course T empAngle + 0 TempAngle + 180 TempAngle + 360 (TempAngle is negative) TempAngle + 180 mpAngle is negative) Resgister Settings Communication between the PIC and GPS system is acheived by the Universal Synchr onous Asynchronous Receiver Transmitter (USART). In this case Asynchronous mode is used. (refer to the PIC 16F777 pdf file, section 11.0 for more detailed infor mation) To enable this serial mode three registers must be set; TXSTA, RCSTA and SPBRG. TXSTA is set in the following manner: Bit 7: 0 Don t care (for Asynchrous mdoe) Bit 6: 0 for 8-bit transmission Bit 5: 0 for transmission enabled Bit 4: 0 for Asynchronous mode Bit 3: 0 this bit is unimplemented Bit 2: 0 for High speed Bit 1: 1 for TSR empty (TRMT) Bit 0: 0 not used in 8-bit transmission Page 63Unmanned Aerial Vehicle SPBRG is the simplest where only a value is entered into the register. Consideri ng asynchronous mode is used and the system is low speed, the following equation is used, where X is the value entered in SPBRG: X FOSC 1 64* BaudRate When a baud rate of 4800bps with a frequency of 8MHz is entered into the equatio n the resulting X value is 25.04, so 25 is the value used in SPBRG. The RCSTA regi ster is set in the following manner: Bit 7: 1 for Serial port enabled Bit 6: 0 for Enables 8-bit reception Bit 5: 0 D on t care for Asynchronous mode Bit 4: 1 to Enable continuous receive (called CR EN) Bit 3: 0 Don t care for 8-bit mode Bit 2: 0 for no Overrun error(OERR) Bit 1 : 0 for no Framing error(FERR) Bit 0: 0 Don t care for 8-bit mode When transmitting input messages to the GPS system to initialize data, the data message had to be inserted in the PIC s EEPROM via MPLAB before programming to P IC (an .ECH file can be created with your EEPROM input by exporting a file (MPLA B), this file is easier to load than re-inputting every time), because it consum ed too much RAM. Data is transmitted bit by bit via the TXREG register, the TSR register must be polled to see whether the bit was sent out or not when TSR is e mpty only can u fill in the next bit. Interrupts are undesired in this mode. Page 64Unmanned Aerial Vehicle For Universal Asynchronous reception, the 6th and 7th bit of the INTCON register must be set, to enable interrupts, along with the 5th bit of register PIE1. An interrupt occurs (bit5 of register PIR is set) under three cases, when a byte is received successfully, when an OERR (Overrun error) or when a FERR (Framing err or) occurs. If a FERR occurs the message is discarded. The message is valid if; the message starts with a $ and ends with 0D 0A, the GPS sends an A in the 19th byte, no FERR error occurs, and the CRC check is correct. If the message is vali d, SPI communication transmits the latitude, longitude and heading to the Main P IC, Also the RF transmits function is called to send this data (for use in the s imulator). This code in detail can be seen in APPENDIX B: CONTROL CODE. Page 65Unmanned Aerial Vehicle 4.4.2 Radio Transceiver This RF device is called a transceiver in the sense that the same unit can send and receive, to and from another identical unit. Operating frequency is 2.4GHz, and data transmission rate can be selected at either 250Kbps or 1Mbps. 250kbps w orks at a longer range of 280m but after testing, range proved to be approximate ly 180m. Also 250kbps improves receiver sensitivity. There are two modes direct mode and shock burst mode. Shock burst works at a lower current and relaxed PIC operation. Low current consumption occurs by using an onboard FIFO to transmit d ata at a low rate then transmit at a high rate. PIC resources are saved by havin g an onboard CRC creator/checker for transmitting/receiving respectively. Pre-amble, address, and CRC are stored on a buffer on the RF then transmitted out, instead of letting the PIC do all this w ork. The transceiver can receive simultaneously on two different channels. Only one channel was used in this project. Pins used Used pins were CE (Chip Enable), CS (Chip Select), CLK (Clock), DR1 (Data Ready1 ), DATA1, Vcc, and GND (1 represents pins pertaining to Channel1). The transceiv er requires a configuration word of up to 15 bytes. This is done through three p ins; CS, CLK and DATA1. Generally CE is turned off, CS is turned on, a delay is done to allow onboard processing, and then data is fed in bit by bit as the cloc k toggles. The Shock burst configuration word is as follows: Shock Burst configuration Word: The section bit[119:16] contains the segments of the configuration register dedi cated to Shock Burst operational protocol. After VDD is turned on Shock Burst co nfiguration is done once and remains set whilst VDD is present. During operation only the first byte for frequency channel and RX/TX switching need to be change d. Page 66Unmanned Aerial Vehicle PLL_CTRL Bit 121-120: Controls the setting of the PLL for test purposes. With closed PLL in TX no devi ation will be present. For normal operational mode these two bits must both be l ow. DATAx_W Bit 119 112: DATA2_W: Length of RF package payload section for receive-channel 2. Bit 111 104: DATA1_W: Length of RF package payload section for receive-channel 1. NOTE: The total number of bits in a Shock Burst RF package may not exceed 256! M aximum length of payload section is hence given by: DATAx_W(bits) = 256 ADDRx (ADDR_W+ CRC) Bit 103 64: ADDR2: Receiver address channel 2, up to 40 bit. Bit 63 24: ADDR1 AD DR1: Receiver address channel 1, up to 40 bit. *NOTE: Bits in ADDRx exceeding th e address width set in ADDR_W are redundant and can be set to logic 0. Page 67Unmanned Aerial Vehicle ADDR_W & CRC Bit 103 64: ADDR2: Receiver address channel 2, up to 40 bit. Bit 63 24: ADDR1 AD DR1: Receiver address channel 1, up to 40 bit. NOTE: Bits in ADDRx exceeding the address width set in ADDR_W are redundant and can be set to logic 0. ADDR_W & CRC Bit 23 18: ADDR_W: Number of bits reserved for RX address in Shock Burst packages. NOTE: Maximum number of address bits is 40 (5 bytes). Values over 40 in ADDR_W a re not valid. Bit 17: CRC_L: CRC length to be calculated by nRF2401 in Shock Bur st. Logic 0: 8 bit CRC Logic 1: 16 bit CRC Bit: 16: CRC_EN: Enables on-chip CRC generation (TX) and verification (RX). Logic 0: On-chip CRC generation/checking disabled Logic 1: On-chip CRC generation/checking enabled Page 68Unmanned Aerial Vehicle This section of the configuration word handles RF and device related parameters. Modes: General device configuration: Bit 15: RX2_EN: Logic 0: One channel receive Logic 1: Two channels receive NOTE: In two channel receive, the nRF2401 receives on two, separate frequency ch annels simultaneously. The frequency of receive channel 1 is set in the configur ation word bit[7-1], receive channel 2 is always 8 channels (8 MHz) above receiv e channel 1. Bit 14: Communication Mode: Logic 0: nRF2401 operates in direct mode. Logic 1: nRF2401 o perates in Shock Burst mode Bit 13: RF Data Rate: Logic 0: 250 kbps Logic 1: 1 Mbps *NOTE: Utilizing 250 kbps instead of 1Mbps will improve the receiver sensitivity by 10 dB. 1Mbps requires 16MHz crystal. Page 69Unmanned Aerial Vehicle Bit 12-10: XO_F: Selects the nRF2401 crystal frequency to be used: Bit 9-8: RF_PWR: Sets nRF2401 RF output power in transmit mode: RF channel & direction Bit 7 1: RF_CH#: Sets the frequency channel the nRF2401 operates on. The channel frequency in transmit is given by: ChannelRF =2400MHz + RF_CH# * 1.0 MHz RF_CH #: between 2400MHz and 2527MHz may be set. The channel frequency in da ta channel 1 is given by: ChannelRF =2400MHz + RF_CH# * 1.0MHz (Receive at PIN#8 ) RF_CH #: between 2400MHz and 2524MHz may be set. The channel frequency in data channel 2 is given by: ChannelRF =2400MHz + RF_CH# * 1.0MHz + 8MHz (Receive at PIN#4) RF_CH #: between 2408MHz and 2524MHz may be set. Page 70Unmanned Aerial Vehicle Bit 0: Set active mode: Logic 0: transmit mode Logic 1: receive mode For more intricate details about the configuration word refer to the nRF2401 dat asheet page 19. Within Shockburst mode there are four different modes. They are displayed in the following table. ACTIVE MODE There are two different options in Active mode, Transmit and Receive . Transmit 1. When the application MCU has data to send, set CE high. This activat es nRF2401 onboard data processing. 2. The address of the receiving node (RX add ress) and payload data is clocked into the nRF2401. The application protocol or MCU sets the speed