Milestone 8

Final Design Report

Team B.Y.O.H.

ENES 100 Section 050112/17/2010

This project’s goal was to create a functioning hovercraft and have it autonomously navigate a pre-arranged course. The team had to divide up the different elements and then bring them together for construction. Gantt charts, computer-generated drawings, and team meetings were all vital tools used to keep designs clear and the team on track.

TABLE OF CONTENTS:

Approvals…3

Executive Summary…4

Introduction…4

Preliminary Design Shortcomings…4

Final Design Details…5

Hull Structure…5

Levitation…7

Propulsion…8

Power…9

Sensors & Actuators…9

Control Algorithm…10

Friction Obstacle…10

Final Design Drawings…13

Construction Details…14

Final Bill of Materials…15

Final Gantt Chart…16

Product Performance…17

Lessons Learned…17

Minutes…18

APPROVALS2

Zain Baqar

John Brennan

Vincent Coburn

Francis Cooper

Christopher Leung

William Neuhauser

Nicole Podesta

Shaan Shakeel

Justin Shive

Nathan Wasserman

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EXECUTIVE SUMMARY

In this project, we planned to build a hovercraft that completed the course

requirements while learning about practical engineering, teamwork, and leadership. By

and large, we accomplished these goals by meeting most milestone requirements on time,

by being flexible with our design to compensate for problems occurred, and by listening

to the ideas and concerns of all team members. In our design we had elements including

base, skirt, plenum, levitation fans, propulsion fans, stepper motors, Arduino, light

sensors, and batteries.

INTRODUCTION

The base was made from a Styrofoam kickboard that was cut in a tombstone

shape. The skirt was made from rip-stop nylon and was attached from the base to the

plenum. The plenum was made of balsa wood, with four holes cut out to augment the lift.

The craft used two lithium ion batteries that powered to the San Ace 80 levitation fan, the

four GWS EDF 40 propulsion fans, and the Arduino. To separate out the voltage, the

circuits included MOSFET transistors. As far as the control system, it consisted of two

light sensors on the front and back underneath so the Arduino could calculate the craft’s

angle difference from the black line. The four propulsion fans were positioned in such a

way that two were in the front attached to stepper motors to facilitate turning, while two

were in the back to provide primary propulsion.

PRELIMINARY DESIGN SHORTCOMINGS

When the project had moved to the construction phase, the team encountered

some difficulties, stemming, in part, from various erroneous elements of the preliminary

design. For instance, when mounting the hardware onto the base, everyone realized that

there was less space than had previously been thought. In all considerations, a larger base

would probably have been more ideal as it would have created more lift and more options

for the orientation of the objects on top.

In addition, the battery voltages that had been selected turned out to be inadequate

to run all electric systems that were needed. In the end, the team decided to purchase

another battery. It ended up being cheaper than the previous battery, so there was an

added budgetary benefit to the revision.4

FINAL DESIGN DETAILS

HULL STRUCTURE

After considering the many options available, including plywood, balsa wood,

and construction foam, it was decided that a foam kickboard would be most ideally suited

for use as the base of the hovercraft (See Figure A below).

Figure A

 (Picture taken from:

http://www.amazon.com/Kickboard-Adult-Large-Made-Shipping/dp/B002FCYT1W/

ref=sr_1_2?ie=UTF8&s=sporting-goods&qid=1287536148&sr=8-2 )

On the website from which the base was purchased, the manufacturer’s stated

weight is 7 ounces. The conversion was made to grams (See Equation 1 below).

Equation 1 7 ounces x 28.3495231 grams = 198.4466617 grams

1 1 ounce

The dimensions of the kickboard are 18.2” x 14” x 1.2”. The kickboard is

composed of high quality cross-linked closed cell polyethylene foam. There are multiple

reasons why this material was decided to be the most advantageous.

First, the material is durable. It is commonly used construction substance in

domestic plumbing and insulation. Second, as evidenced by the results of Equation 1, the 5

material is very light-weight. Since budgeting weight is an essential component of the

project as a whole, this choice was able to provide the best of both weight and strength.

Third, the material came at a very cheap price of $12.99.

There will, however, be some issues that have to be addressed as a result of the

properties of this base. For instance, it may be too light to properly balance the objects on

top, so extra weight may need to be added when the craft is tested. Also, since it is foam,

glue must be applied very carefully to make sure that the additions stay put. Surface area

might also be an issue in the future, because the kickboard is of a concrete size.

Therefore, the fans, batteries, wires, and sensor must be arranged very deliberately. A

secondary kickboard will be cut out for a plenum and attached via balsa wood. However,

it must be sensibly considered for its addition to weight and cost.

Another consideration for effectively building the craft was the moment of inertia.

To calculate this figure from the data provided, one used the basic equation I=mr^2.

However, since the figure is clearly not circular, it was necessary to calculate the average

radius. The hovercraft can be broken down into the following dimensions (Figure B).

Figure B

4 inches

14.2 inches

14 inches

As a result, assuming that the moment of inertia will occur at the center of the

craft, if one calculate the area of the entire base, and then equates it to a circle with equal

area, one would be able to find the average radius of the base (See Equation 2).

Equation 26

(14 in*14.2 in) + (49pi/2 in2)= 275.76902 in2

275.76902 in2=pi(x2)

x = 9.369 in =. 2379751 m = average radius

I=m(r2)

I = (.1984466617 kg)(.2379751 m) 2

I= .0112384608 kg/m2= moment of inertia

LEVITATION

For levitation purposes the San Ace 80 will be used, operating at 12V and 5.5A.

This fan choice will easily be able to provide our craft’s required Δp of 136.6 Pa and Q of

2.26 m3/min (see below), and give a reasonable margin for error should the design’s

weight increase. With the current weight budget, however, both detuning the fan and

venting the airflow through the rear of the hovercraft are being considered to conserve

our optimal hover height and, in the case of the latter, provide additional forward thrust.

Δp=mgAp=

(1.50 )(9.8).108m2 =136.6 Pa

Q=hgap l√ 2mgρ A p

=( .002 ) (1.25 )√ 2 (1.5 ) (9.8 )(1.2 ) ( .108 )

= .0377m3

sec=2.26m2

min

PROPULSION

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One of our main considerations while designing our hovercraft was weight.

Newton’s second law states that mass is inversely proportional to acceleration, so the

smaller the mass, the greater the acceleration (assuming the Fnet is constant). Our

hovercraft will most likely be less than 2kg, so the propulsion system will not need to

provide a very high thrust force in order to provide ample acceleration. We will be using

four GWS EDF 40 fans, with one placed at each “corner” of our base. The GWS EDF 40

fans are optimal for our hovercraft because they start and stop immediately. Most other

fans take time to get going, and take time to slow down to a stop. This delay in thrust, and

residual thrust can result in waddling down the course. The front two fans will be

connected to a stepper motor and steer together, and back two fans will be connected to a

stepper motor and steer together. These two independent systems will allow for

maneuverability as well as stability. Assuming all four fans are on at full power, and all

four fans are pointed in the same direction, the maximum thrust force is 3.412n. The

calculation for maximum thrust force is as follows:

P=113 n/m2

A=.1076m2

k=.3

Fn=Fw-Fp

Fn=(1.5)(9.8)-(136.6)(.1076)=.0876n

Ffr=Fn*k=(.0876)(.3)=.0262n

Ft=3.412n

Ft-Ffr=ma

3.412-.0262=(1.25)a

a=2.7m/s2

The success of our hovercraft is determined by its ability to rotate around its

center of mass. If it is unable to rotate, it will be unable to follow the black line. Just as

mass is important in determining linear acceleration, the moment of inertia is important in

determining angular acceleration. Since our base is roughly a thin circle, the equation for 8

our moment of inertia is I=(.5)(mr2). The mass is approximately 1.25kg, and the radius is

about .29m. This gives: I=.05kgm2. Assuming there is zero friction, all both sets of fans

perpendicular to the center of mass, and both sets of fans are in opposite directions; the

calculation for angular acceleration is as follows:

Tnet=I

Tfan1+2+Tfan3+4=I

RFsin()+RFsin()=I

(.29)(1.706)sin(90)+(.29)(1.706)sin(90)=(.05)

=19.8rad/sec2

POWER

The hovercraft will be powered by two independent batteries one 14.8V

3000mAh unit and one 11.1V 8000mAh unit. The 14.8V pack will supply the lift fan,

Arduino, and sensors, while the 11.1V battery is designated for propulsion duty.

Estimated run time is approximately 25 minutes. Please see schematic for power

modulation.

SENSORS AND ACTUATORS

The hovercraft’s main sensor capabilities will be provided via two arrays of photo

sensors located outboard of the hull at the front and rear. These arrays, of 8 sensors each,

will provide immediate and exact notification of any deviation from the line at the front

or rear and relay the information gathered to the independent front/rear thrust vectoring

systems. These signals will become physical movement through stepper motors that

drive two independent pairs of propulsion fans via drive belts.

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CONTROL ALGORITHM

The final code

FRICTION OBSTACLE

The thrust provided by the four GWS EDF 40 fans will be more than enough to

enable the hovercraft to maintain velocity through the friction obstacle, but the absence of

a line on the track prompts a transition to a secondary sensing system. Ultrasonic sensors

will be mounted 10 cm inboard (to avoid bottoming-out) on either side of the craft and

will be the primary source of input to the control system exclusively for the duration of

the friction obstacle.

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CONSTRUCTION DETAILS

The hovercraft was composed of many essential parts. It consisted of a base, skirt, plenum, lift fan, four propulsion fans, two batteries, an arduino controller, and light sensors.

The base was made from a kickboard composed of high quality cross-linked closed cell polyethylene foam. It had a mass of 198.45 grams, and its dimensions were 18.2” x 14” x 1.2”. Its curved base end was cut into a straight line with the foam wire cutter so it would resemble a tombstone shape.

The skirt was made of two different materials, with the back and middle parts being high-quality rip stop nylon, and the front section being a plastic bag. A plastic bag was used for the skirt for the front end because the front end is curved, so a plastic bag was more flexible and therefore better suited to wrap around the curve tightly without creating large folds on the bottom that could create drag. The fabric was cut with an X-acto knife in the shape of a long rectangle, and then it was wrapped around the base and plenum and glued to each of them with high strength polymer glue.

The plenum was constructed from balsa wood. It was cut into the same shape as the base with a wood cutter, but with a height and width one inch smaller. Four circular holes were cut equi-dimensionally from each corner with the wood hole cutter, each with a diameter of two inches to allow for even air flow. The plenum was superglued under the base by two 2” foam cubes, and the skirt was glued connecting the perimeter of the plenum to the perimeter from the base, so that no air could escape except from the holes in the plenum.

The lift fan was placed at the point of the center of gravity of the base. The lift fan used by the team was the San Ace 80. A circular hole with a diameter of ( ) was cut out from the base with the circular saw so that air from the fan could flow into the skirt and through the plenum. The San Ace 80 was then glued to the base with ()

Four GWS EDF 40 propulsion fans were also used. Appropriate fan guards for the front and back were created out of wire sheets, which were sized appropriately with wire cutters and then taped over the fan so not to interfere with the movement of the blades. One fan was place in each corner of the base and attached to a stepper motor, which was stabilized by being glued into a foam block. This block was glued to each corner of the base, and each motor was then connected to the battery by wires.

The arduino control system was the brain of the hovercraft. It was connected by wire to all of the sensors and the battery. The batteries used were lithium ion, one 14.8V and the other V. They were superglued directly behind the lift fan so to keep the hovercraft balanced. The light sensors were attached to the front and back of the base of the hovercraft via foam blocks. The foam blocks were glued to the base in a way so to allow the sensors to be as close to the ground as possible, so it could better follow the black line.

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FINAL BILL OF MATERIALS

Product PurposeWeight (g) Price

Electrical Load (mA) Voltage

San Ace 80 Lift Fan 350 $ 58.66 5500 12

Arduino Microcontroller 31.05 $ 19.99 18.7 7 to 12

Arduino Sensor ShieldAdd. Sensor Inputs

$ 9.89

Kickboard Base 194.3 $ 14.99 N/A N/A

GWS EDF 40 (4) Propulsion Fans 108 $ 41.50 19600 8.4

Batteries (2) Power Supply 336 $ 99.90

1/8" Balsa Wood Plenum 54.68 $ 14.97

Rip-Stop Nylon Skirt 1.54 $ 11.50

Transistors (10) $ 15.90

Resisters (20) $ 4.00

Connector Wires $ 2.97

CA Glue $ 6.00

Stepper Motor (2) 154 $ 14.00

Drive Belt $ 5.00

Line Sensor Array $ 11.00

Proximity Sensors (2) Sand Trap Nav. $ 50.00

Total: 1229.567 $ 380.27 25118.70

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PRODUCT PERFORMANCE

The team’s first and foremost testing priority is to verify the capability of the

externally sourced Arduino microcontroller. Following its successful evaluation, the

remainder of the construction materials will be gathered and the effectiveness of the

cyanoacrylate glue will also be double checked.

LESSONS LEARNED

So first and foremost is the obvious struggle of using two different types of sensors.

Because we chose to go with IR sensors we needed another way to navigate the sand trap.

This required the edition of proximity sensors. The two sets of sensors are going to make

our code a little difficult to create. On a different note because we have chosen to go with

a belt steering system creating the circuits necessary for our intricate design is going to be

a hassle. Also related to the belt system is the way of powering it we are going to need a

very strong battery with a long life span to last the entire course. Of course keeping the

wiring neat is going to be a challenge with all the circuits we are creating, but that is

easily solvable with good planning. Aside from these major difficulties the only issues

that are going to come up are the ones we don’t know which I'm sure there are plenty of,

but life is a learning experience and you learn from your mistakes.

MINUTES

Meeting 1 9/12/10

- Research Groups:o Fan: Propulsion/Steering- Chris & Vinceo Fan: Lift- Zain & Justino Microcontroller/Batteries/Sensors: Nathan & Willo Base: John & Nicoleo Skirts- Frank & Shaan

- Goals:o Gather pricing optionso Info/Purchasing sites

- Websites:o www.rchovercraft.como Create a Facebook team website

Meeting 2 9/19/10

- Research groups: plan slides- Select speakers for first presentation- Website published- Plan to finish and turn in slides by 8am Tuesday- Skirt group to go to Matlab

Meeting 3 9/26/10

- Meet in specialized groups- Groups confer on their object selections- Purchases narrowed down/price compared- Skirt options discussed from Matlab- Weight range decided (1-2kg)

Meeting 4 9/29/10

- Discuss goals/Gantt chart- Fan purchased- Kickboard base purchased- Start buying materials

Meeting 5 10/6/10

- Prepare for next milestone- Discuss AutoCAD (Autodesk inventor)- Illustration/ structure plans

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- Fan bought online received: San Ace 80- Orientation of objects on base- All main items purchased and shipping

Meeting 6 10/10/10

- Propulsion Fans ordered; Control Fans ordered - Kickboard base received- Preliminary plenum design discussed- Ripstop nylon skirt researched

Meeting 7 10/13/10- Divided up responsibilities for presentation- Discussed/outlined requirements for new milestones

o Oral Presentationo Design report

2,3 pages per group Design drawing

- Placement of fans/ number of fanso Farther out = more torqueo Four corners, possible two in middle

- Control scheme examinedo Stepper motors

- Propulsion GWS fans on their way- Sensors/wires to be purchased this week- Plenum research

Meeting 8 10/17/10

- Calculations made for Milestone 3- Slides finished and compiled- Subgroups separated

o Review of their purposeo Review details for presentation

- Report compiled and formatted- Presentation members decided- Presentation practiced

Meeting 9 10/24/10

- Fans received- Nylon received- Confirmed Arduino is in working order- Ordered D-multiplexers- Looked into bipolar stepper motors- Budget reviewed

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- Planned out preliminary construction

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