Milestone 3

Preliminary Design Report

Team B.Y.O.H.

ENES 100 Section 050110/20/2010

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TABLE OF CONTENTS:

Approvals…3

Executive Summary…4

Preliminary Design Details…4

Hull Structure…4

Levitation…7

Propulsion…8

Power…9

Sensors & Actuators…9

Control Algorithm…10

Friction Obstacle…11-12

Design Drawing…13

Bill of Materials…14

Gantt Chart…15

Construction/Testing Plans…16

Anticipated Difficulties…16

2

Approvals

Zain Baqar

John Brennan

Vincent Coburn

Francis Cooper

Christopher Leung

Nicole Podesta

William Neuhauser

Shaan Shakeel

Justin Shive

Nathan Wasserman

3

Executive Summary

In this project we plan on building a hovercraft that will complete the course

while learning multiple things about both engineering as a physical activity and the

mental aspects being teamwork and leadership. We will accomplish these goals by

meeting milestone requirements on time and be flexible with our building design to

account for problems that may occur and lastly by paying attention to what we are

doing and how everything works together to create the final product. In our design

we have our base, skirt, plentum, levitation fans, propulsion fans, control system

and sensors, and lastly our batteries. Our base will be made from a styrafoam

kickboard that will be cut to form a tombstone shape. Our Skirt will be made from

ripstock nylon and will be a soft skirt with fingers attatched to the outside if

allowed. Our plentum will be made of balsa wood. We will use lithium Ion batteries

that will give power to our san ace 80 levitation fan, our gws edf 40 propulsion fans,

and our arduino. We will separate out the voltage through our mosfet transistors.

And our control system will consist of two proximity sensors for the friction part of

the course and multiple light sensors on the front and back underneath the craft so

we can calculate our angle difference from the black line. Our propulsion fans will

be constantly running and our turning will occur do to our propulsion fans being

attached to two stepper motors on the front and back.

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).

4

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 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.

5

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).

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Equation 2

(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 p of 136.6 Δ

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.

7

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 )= .0377m

3

sec=2.26m

2

min

Propulsion

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=3.412nFt-Ffr=ma

3.412-.0262=(1.25)aa=2.7m/s2

8

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 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=ITfan1+2+Tfan3+4=IRFsin()+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.

9

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.

10

11

12

13

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

14

Construction and Testing Plans

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.

Anticipated Difficulties

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.