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Final Design ReportDecember 14th 2009
: The Second Team in Section 0201 in ENES100.
I pledge on my honor that I have not given or received any unauthorized assistance on this
assignment.
-University of Maryland’s Honor Pledge
(http://www.studentconduct.umd.edu/info/students/a_honorpledge.aspx)
Name Signature Date
Justin Chen _________________________________ ______
Derek Dechent _________________________________ ______
William Dunham _________________________________ ______
Rachel Fan _________________________________ ______
Omar Ali Khan _________________________________ ______
Lisa Liu _________________________________ ______
Julianna Magnus _________________________________ ______
Daniel Silversmith _________________________________ ______
Mark Weniger _________________________________ ______
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Table of Contents
Executive Summary..........................................................................................................................................4
Introduction..........................................................................................................................................................5
Preliminary Design Shortcomings...............................................................................................................6
Structure................................................................................................................................................................7
Skirt........................................................................................................................................................................ 8
Center of Mass....................................................................................................................................................9
Arm/Gate Activation........................................................................................................................................ 9
Levitation Fan...................................................................................................................................................10
Propulsion System..........................................................................................................................................12
Power...................................................................................................................................................................14
Sensors................................................................................................................................................................15
Actuators............................................................................................................................................................ 16
Control Algorithm...........................................................................................................................................16
Product Development Review....................................................................................................................20
Product Performance......................................................................................................................................20
Bill of Materials...............................................................................................................................................22
Appendixes........................................................................................................................................................24
Appendix A: Drawings, Figures, Lists and Charts..........................................................25
Appendix B: Meeting Minutes............................................................................................. 38
Appendix C: Construction Details......................................................................................40
Appendix D: Gantt Chart..................................................................................................... 47
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Executive Summary
The goal of this project is to design a hovercraft that could autonomously navigate the
designated course. The deadline is December 4th, and this team, team IDC, completed the
hovercraft on December 11th, 2009.
The weight of this hovercraft is 1750g and its gap height is 2.5mm. It’s axial levitation
fan provided the needed .38inH20 of pressure and 91.1 CFM, enough to lift the craft off the
ground.
A rip-stop nylon skirt was attached using a MATLAB template. A single propulsion fan
attached to a servomotor was used to steer the craft, and provided .63N of thrust.
A 14.8V 2200mAh Li-ion battery pack was used to power the levitation and propulsion
fan. With a capacity of 2200mAh and a required 3.25A for the two fans, the hovercraft can
levitate for about 40 min using this Li-ion battery pack.
The hovercraft can autonomously navigate the course using a combination of light
sensors and ultrasonic sensors that relay data back to the NXT. The distance sensor, once it
senses that the hovercraft is directly under the button, causes the NXT to raise the arm, a L-
shaped piece of foam attached to a Styrfoam base that can raise to push the button and lower to
clear the gate. Light sensors inform the NXT when the hovercraft is no longer on the black tape,
and the NXT adjusts the servomotor the propulsion fan is on to turn the hovercraft so that it can
follow the course.
All fans are equipped with grills for safety reasons.
The team operated under a budget of $350, and came in under budget, at $315.
This final design report goes into a detailed explanation of the hovercraft’s system, Team
IDC’s structure, and all other pertinent details. It includes equations, charts, drawings and figures
to better aid in the proof of Team IDC’s design concept.
4
IntroductionThe objective of this project was to gain an insight into the design process an engineer
must go through to create a viable prototype. As students who wish to become engineers, it is
crucial that one learns that engineering is more than just coming up with a good idea, it also
entails presenting one’s ideas in a clear and concise manner, proving and defending one’s ideas,
and following through on the construction of the object, not just stopping at the theoretical, but
making one’s theory a practicality. By building a hovercraft, one gains invaluable knowledge on
how to follow through on a concept and make it a reality, and also learns about the many, many
things that will go wrong on a project, and how to deal with these problems once they come up.
Team IDC has created a viable, working hovercraft. The weight of this hovercraft is
1750g and its gap height is 2.5mm. It’s axial levitation fan provided the needed .38inH20 of
pressure and 91.1CFM, enough to lift the craft off the ground. A rip-stop nylon skirt was
attached using a MATLAB template. A single propulsion fan attached to a servomotor was used
to steer the craft, and provided .629N of thrust. A 14.8V 2200mAh Li-ion battery pack was used
to power the levitation and propulsion fan. With a capacity of 2200mAh and a required 3.25A for
the two fans, the hovercraft can levitate for about 40 min using this Li-ion battery pack. The
hovercraft can autonomously navigate the course using a combination of light sensors and
ultrasonic sensors that relay data back to the NXT. The distance sensor, once it senses that the
hovercraft is directly under the button, causes the NXT to raise the arm, a L-shaped piece of
foam attached to a styrfoam base that can raise to push the button and lower to clear the gate.
Light sensors inform the NXT when the hovercraft is no longer on the black tape, and the NXT
adjusts the servomotor the propulsion fan is on to turn the hovercraft so that it can follow the
course. Final construction details can be found in Appendix C. All fans are equipped with grills
for safety reasons. The team operated under a budget of $350, and came in under budget, at
$310.
To create a successful design, it is crucial that individuals work together as a team. It is
essentially impossible for any one person, given the experience a first-year college student has,
to build this craft on his or her own. To that extent, this team has divided this project into three
co-dependent sub teams: structure and power, propulsion and levitation, and control and sensors.
While each team has individual components they are responsible for, all the teams must work
5
together for the project to be successful. Regular meetings and frequent e-mails are necessary to
maintain all of this. A detailed minute meetings can be found in Appendix B.
This final design report goes into a detailed explanation of the hovercraft’s system, Team
IDC’s structure, and all other pertinent details. It includes equations, charts, drawings and figures
to better aid in the proof of Team IDC’s design concept.
Preliminary Design Shortcomings
The original design called for both decks to be made out of Styrofoam, but in order to
save on material, the team decided to make the lower deck out of cardboard the
Styrofoam came in.
The T shaped arm became a L shaped arm so that it could rotate continuously in a circle.
This helped the hovercraft deal with not coming in perfectly straight or hitting the button
the first time.
The initial design did not account for how to mount the distance sensor. A large base was
built so that the distance sensor could rest on top of the light sensors, which made the
hovercraft rather top heavy, meaning the center of mass needed to be altered.
The team never made specific plans on the counter-rotating grooves, and as a result, had
to make the design as the hovercraft was built. It was tested by turning on the levitation
fan and making sure that the hovercraft did not spin at an unreasonable rate. A little spin
was fine; the propulsion fan can account for that, but too much spin would make the
hovercraft too difficult to control.
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StructureTeam IDC decided to use foam for the construction of the structure because of how easy
it was to cut into various shapes and due to its low price. Researching on the Internet, the team
decided to use 2” thick EPP foam because it was recommended for projects similar to this one, it
was lightweight at 1.3lbs/cu.ft., and it was relatively inexpensive. The structure was a double
deck octagon. Originally, the preliminary design plan called for a circular structure, but it was
soon discovered that soft skirts do not attach well to round shapes. As a result, the circle became
an octagon: something with straight sides that is still close to a circle, that maximizes area while
minimizing perimeter.
The structure contained two decks in order to create a
space for pressure to build up. The counter-rotation spirals,
as well as small piece of support foam, connected these two
decks, both made out of the same foam. See Figure 10:
Counter-rotating Grooves for details. As the levitation fan is
axial, the air underneath the hovercraft will actually be
spinning. This air current can cause the hovercraft itself to
constantly spin in counter-clockwise. The spinning would cause the hovercraft to become very
difficult to control, so between the two decks will be a spiral in the clockwise direction. This
spiral has four arms that are 13mm thick and take up the 25mm high gap between the two decks.
This spiral should stop the air current from forming when the air hits the arms and is forced to
move in another direction. For specific positions, see Figure 4: Center of Mass Diagram in
Appendix A.
Lessons Learned
The original design call for both decks to be made out of Styrofoam. However, it was
decided that to save on materials and lower the height of the hovercraft, the lower deck would be
made out of the cardboard box the foam came in. That way, lots of leftover foam was available
to make the arm and sensor unit out of. This team recommends that future teams have plenty of
extra foam, as the smaller parts often have to be rebuilt several times, and having extra foam
handy means less trips to the store.
.46m
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Skirt
The team chose rip stop nylon as the material for the soft skirt through careful
consideration. In order to make this decision, several other choices were researched and
evaluated. The material needed would have to be airtight and not easily ripped. One of the
options considered was to make the actual material for the skirt in house. The team could have
bought canvas and painted it with a coat of liquid latex. The material itself would be very sturdy
as the fabric is canvas. However, it was decided that the overall process would be too much to
repeat if a mistake were to be made in the construction or testing of the hovercraft. Also, the
material would create excess friction between the hovercraft and the track. Another possibility
considered was to use vinyl, the fabric that most raincoats are made with. The problem it
presented was that the truly sturdy type was expensive and out of the team’s price range. While
enough fabric for one skirt would have been affordable, realistically, mistakes happen, and it
needs to be acknowledge that it might become necessary to buy extra materials, and buying extra
vinyl would have put the team way over budget.
The decision was made to use rip-stop nylon, a smooth and durable material. This is a
material that is known to work and was recommended by most ENES students and professors.
The fabric itself was also not very expensive at $6.99 per yard. Also, unlike the other fabrics, the
rip-stop nylon is easily attained. It is a very common fabric that can be found at JoAnn’s fabric
and craft store. There’s no need to wait for shipping or paying the fee in case a mistake is made
in constructing the skirt.
The skirt was attached using duct tape to the upper deck of the hovercraft. It will be cut
and shaped with the help of MATLAB. See Figure 5 : Skirt Template to be used for
Construction in Appendix for more details.
Lessons Learned
The team used MATLAB to make a skirt template, however, the team did not leave an
extra inch around the MATLAB template when cutting out the fabric, and as a result, the initial
cutouts could not be sewn together and the team had to start over again. Fortunately, the team
had bought extra fabric so this was not a major setback. Team IDC strongly suggests that other
8
teams buy extra fabric as well, as it is not too expensive and having extra materials on hand
saves a lot of time.
Center of MassThe center of mass of the hovercraft is where all the mass combined of the hovercraft is
concentrated on. It is the point that the hovercraft will be turning around. In order to calculate
the center of mass, the weight and location of all masses located on the hovercraft’s deck. Table
3: Weight Table in Appendix A has all masses of significance. It is important to note that the
main structure composed of the top deck, counter rotating grooves, skirt, and bottom deck were
included because the expected center of mass is off center. Masses not included were the wiring
or circuits because they do not add a significant weight to the hovercraft. See Figure 4: Center of
Mass Diagram in Appendix A for more information.
Center of massM1* x1 M2 * x2 .... Mn * xn
M1 M2 ... Mn
The center of mass is off center of the structure towards the front and to the left at
(0.636,-0.323) inches. For the competition, weights were placed in the back right of the craft’s
deck to move the center of mass back to the center so that the controls would be more effective
in moving the craft.
Arm/Gate ActivationThe team has created a rotating arm that will be employed to activate the gate, and this
arm and base will be created from the leftover foam. Foam was the best choice because it is
lightweight, sturdy, and readily available. The arm was propped up on a base made out of foam
9
to minimize the torque placed on the servo motor, but the height of the base has changed from
the preliminary design. In the original design the bottom deck was also foam, but the team
decided that cardboard was a much more suitable material because it was thinner and much
lighter. However, this significantly decreased the overall height of the hovercraft. This meant
that the base had to be made taller to compensate for this change.
The servo motor is placed on top of the base and the arm is attached to the motor. The
shape of the arm was altered from an “I” shape to an “L” shape so that it could spin continuously
in a circle until it activated the gate, and this gives the team a much better chance of success. The
arm was also made smaller than what was specified in the original part, and this was due to the
fact that too much weight at the top of the base would create an unbalanced craft.
Lessons Learned
The gate activation was one of the hardest Milestones to accomplish. It was learned
that it is wise start designing a way to open the gate early, but the actual construction of the arm
should wait until the rest of the hovercraft is completed. The team had to constantly resize the
base and the arm due to slight changes in the height of the hovercraft, and it was an unnecessary
waste of time and materials to keep rebuilding the arm.
Levitation Fan
The mass of the hovercraft is listed as the sum of the mass of its parts and was measured
to be 1676 grams. A detailed listing of each individual mass can be found Table 3: Weight Table,
in Appendix A.
The weight of the hovercraft is 17.13 Newtons.
10
D =.4572 meters
a b
Next, the plenum deck area was calculated. The area of an octagon can be found in
numerous ways and was calculated using two variables, a and b, in the following:
.1732 m²
The required plenum pressure can be calculated by dividing the weight of the hovercraft
by the area of the plenum deck, as seen below.
The last step necessary in finalizing the calculations of the required pressure is to convert
the pressure from Pascals to inH₂0 (.00401 inH₂O = 1 Pa).
11
Next, the team calculated volumetric flowrate. Using a hover height (hgap) of 2.5 mm, the
team calculated the perimeter of the octagon to be 1.397 m. From these two pieces of
information the gap area was calculated.
The exit velocity can be determined from the formula:
Now all that’s left to do is calculate the required flow rate.
Based on these two numbers, an EBM PAPST fan was chosen and ordered.
Lessons Learned
The weight of the hovercraft changed quite significantly from the initial calculation of
weight-it was actually close to 400g over, mainly because of overestimating the weight of the
Styrofoam, and not realizing that only one battery was needed to lift the hovercraft. This threw
some of the other calculations off, specifically how tall to make the arm. Fortunately, none of
these were seriously problems, we just needed slightly heavier counterweights. This team highly
recommends to future teams that they get a fan that is well under the pressure v. flowrate curve,
just in case in turns out they underestimated how much weight, as having to order a new fan at
the last minute would have been a major setback.
Propulsion System
The fan that will be used for the hovercraft’s propulsion is the Vantec Tornado TD8038H. It was
chosen due too it’s power and relatively low cost.
The fan’s thrust is calculated by the equation:
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Where Q is the airflow, ρ is the density of air which is given as 1.2 kg/m3, and Ao is the
fan blade area. The fan blade area is found using the formula to find the area of the circle and
using the diameter found on the fan’s fact sheet online [1]. The diameter is 80mm so the radius is
40mm or 0.04m.
The only remaining variable is Q, which is found on the fan’s fact sheet as the fan’s max
flow rate as the fan will produce no change in pressure. The max flow rate is 84.1CFM, as
gotten from the fans data sheet.
The thrust comes out to 0.629N. Next, the acceleration that will be produced must be
calculated. The mass used is 1676g or 1.676kg.
The calculated acceleration is 0.375m/sec2. This might seem a bit high, but the actual
acceleration will be offset by the winding motion our control scheme as the fan will never
actually be pointed directly forward.
The max angular acceleration is found at the maximum angle the servo motor will be
turning the propulsion fan. The controls code puts this maximum angle at 60 degrees. The fan is
203mm from the center of mass.
Again, it is worth noting that the full acceleration will almost never be enacted on the
hovercraft. With the winding motion, there will always be some combination of a circular and
linear acceleration that are both less then the maximum.
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Power
The main power to the actuators will be provided by one 4-cell 14.8 V 2200mAh
rechargeable Li-ion battery pack. The mass of this battery is 0.17 kg; the dimension is 73.7mm L
x 71.4mm W x 17.8mm H. The Li-ion pack will have 4 cylindrical cells with PCB (printed
circuit board) and poly switch for full protection against overcurrent faults in electronic circuits.
The battery pack also has a built-in IC (integrated circuit) chip that will prevent the battery from
over charge and over discharge, which will prolong battery life.
The maximum discharge current for this Li-ion battery is 5A, which is enough for our
levitation and propulsion fans. The cut-off voltage is 12V, so when the Li-ion battery senses a
voltage of 12V or less, the battery will stop discharging. Since the cut-off voltage is 12V, the
fans will stop rotating when the battery reaches the cut-off, meaning the fans will always operate
at the optimal 12V performance with a voltage regulator. This will prevent over discharge and
indicate when the battery needs to be charged for optimal fan performance.
The Li-ion battery pack will individually power the levitation fan and propulsion fans
through transistors. The lift and thrust systems will be put in parallel so the voltage will travel
down, making the maximum voltage 12V. A voltage regulator will decrease the input voltage
from 14.4V to 12V and keep it at a constant and steady 12V value. The NXT will control the
amount of current distributed to the fans through the transistors, letting it turn the fans on and
off.
In compliance with the design requirements, the batteries must last at least 10 minutes.
The current draw from the levitation fan is 2.5A, and from the propulsion fan is 0.75A. The
battery has a capacity of 2200mAh or 2.2Ah. To find the amount of time the battery would last
with a 3.25A draw, divide the capacity by the current draw to get 0.68 hours. Multiply 0.68 by
60 to yield approximately 40 minutes of levitation and propulsion time. Therefore, the Li-ion
battery pack can successfully provide enough current to let the hovercraft levitate for over 10
minutes.
The NXT will distribute the power to the sensors and servo motor because they will be
directly attached to the NXT. The NXT contains its own batteries so the Li-ion battery pack will
not be used to power the NXT or the sensors/motor attached to it. A diode will also be used to
protect the NXT from reverse current. The NXT provided a PWM (pulse width modulated)
signal to control a power MOSFET transistor to use it as a throttle for the propulsion fan. The
14
NXT sends a modulated voltage to the propulsion fan while a consistent 12V is sent to the
levitation fan.
Lessons Learned
An important lesson learned from the Li-ion battery pack was to expect the unexpected.
The first Li-ion battery pack that was used did not work. The battery did not output any voltage,
so the team had to use the back-up Li-ion battery pack. Therefore, a team should always have a
back-up plan or item to use in case of malfunctions.
Sensors
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To follow the course IDC had two options: follow the line or follow the wall. First the
team considered following the
wall. This was decided too
complicated for several reasons.
One problem was the angle of the
hovercraft. The sensors and
controls sub team realized that the
program, and the course, would
cause the hovercraft to rotate.
When it rotated, the distance
sensor (ultrasonic sensor) would
read incorrect values to the NXT
brick. Even if the team used multiple ultrasonic sensors in order to attempt to correct for the
angle, the program could easily fail if the team made an incorrect calculation. Instead, IDC
decided to follow the line using three Lego light sensors. Team IDC realized that the closer the
light sensors were together, the less the hovercraft would navigate off course, thus the light
sensors were placed the minimum distance apart. With one placed in the center so that it would
be on the black line, two more would be placed so that they were not on the black tape: 51mm on
either side of the center one, to accommodate 100mm tape.
In order to open the gate, the team would need more than just the three light sensors. The
team decided that an ultrasonic sensor could easily detect when to open the gate, by causing an
activation segment of code to be entered at a certain distance from the gate. This sensor would
be place in front of the hovercraft, and centered. These four sensors complete the sensor array.
Lessons LearnedTeam IDC used three light sensors in the front of the hovercraft to navigate the line and
an ultrasonic sensor to sense when the gate opened during the gate activation section of the
course. There were no problems with the three light sensors. The navigation of the black line
went smoothly. The only problems (relatively minor issues) was with the ultrasonic sensor. In
theory, this sensor worked very well. It would sense the gate, the arm would spin, activate the
gate, the gate would go up, and then the arm would stop. In practice, however, the arm did not
stop spinning because the sensor had trouble distinguishing between the cases where the gate
Figure 1: Sensors
16
moved and where the hovercraft rotated. In retrospect, a touch sensor would have made gate
activation a lot simpler and would have allowed for a more successful hovercraft.
ActuatorsTeam IDC decided to use four actuators, three of which were controlled by the NXT.
The three actuators controlled by the NXT were the propulsion fan and two servomotors: one
motor controlled the propulsion fan’s direction and the other controlled the hovercraft’s arm
(used for gate activation). The two servomotors were simply connected to the NXT through
Lego connector cables in ports A and B. The propulsion fan was connected in parallel to the
levitation fan in order to get power from the external lithium ion batter pack, but the amount of
voltage it received was controlled by the NXT through a transistor. The voltage output to the
transistor caused a proportional increase in the current given to the propulsion fan. The last
system is the levitation fan. This would be regulated down to 12V using a voltage regulator, and
would be switched on manually. It would not interact with the NXT, instead, would get it’s
power directly from the battery.
Control AlgorithmFirst, the variables are declared.
Next, the first loop handles execution before the gate.
While within the first loop:
- Continuously update light sensors
- Continuously update sound sensor
- If a sensor is on black, turn away from that sensor
- If the gate is nearby, start spinning the arm
- If gate has been raised, lower arm and proceed to second loop
While within the second loop:
- Continuously update light sensors
17
- If the hovercraft is straight, continue going straight
- If one of the side sensors are black, turn towards it
See the Table 5 : Position of Hovercraft and Algorithm Response and the full code in Appendix
A for further information.
Circuitry
The majority of the electronics is made up of
the NXT and Lego devices with only a small portion
requiring custom circuitry. The microcontroller and
associated Lego sensors are prebuilt and modular and
is denoted on the schematic by the device type
symbol prefixed by “Lego” with no elaboration of the
internal schematics. As these are modular, there is no
assembly required, only an NXT cable is needed to
connect them to the NXT:
Connecting a Lego Device:
1. Connect one end of the cable to the port specified in the schematic (Ex. “Input Port 1”)
2. Connect the other end to the Lego device (Ex. “LS1”)
Repeat this procedure for the remaining Lego devices using the Wiring Schematic found in Appendix A.
This completes the simple aspect of the hovercraft electronics assembly.
A custom circuit had to be made to regulate power to and control the levitation and
propulsion fans. The circuit design requires a 3A 12v voltage regulator, 3A variable voltage
regulator, power MOSFET capable of switching up to 3A at 12v, diodes and the associated
resistors. All the specific part model numbers used by our team are indicated on the schematic
except for resistors R1 and R2. The resistance values of these two resistors are used in a ratio to
determine the variable voltage; more information in the notes. A variable resistor of up to 10k
Figure 2: Main Power Supply Circuit
18
ohms was used for R2 and 1k ohm for R1. See Figure 11: Wiring Schematic in Appendix A for
more detail.
The team used two different mediums for the circuitry: a Breadboard for prototyping, and a Perf
board for the final circuit.
Use Figure 12: Top and bottom of finished circuit provided in Appendix A to construct the
circuitry on the perf board.
Basic use of a perf board:
1. Map out where all the parts will go and any wire jumps if necessary
2. Insert legs of component into appropriate holes
3. solder the legs in with a little amount of solder
4. cut off the excess leads
5. For wire jumps, strip about 4 mm
on both ends
6. Use little solder to solder the wire
strands in. It should be little
enough that non sticks out but if
so, cut it.
7. Hot glue any wires connecting to
the board ( to prevent wires from
developing physical stress breaks)
8. check for errors
Apply this operation to all the parts for the completed circuit.
Figure 3: Propulsion Fan Circuitry
19
Lessons LearnedWhen building a circuit onto a perf board, it helps tremendously to pre plan the placement of all
components and any wire connections between them, not just use a schematic as that doesn’t
show the physical placement of the components. Soldering two adjacent joints that aren’t
connected is rather time consuming, messy, and error prone; A short wire bridge should be used
or some other method. Instead of creating “traces” using wires, they can be etched out and if
done correctly would be quite reliable. Also prototyping on a breadboard or on some medium
that allows for quick removal and debugging is a must; a perf board setup is more permanent and
is difficult to edit.
It is always better to double and triple check connections and put in safety and high
quality mechanisms(diodes, heatsinks, active cooling, master power switches, modular
connections)than to hastily achieve a desirable outcome. Since this was followed, no
components were damaged, which could have cost the team weeks in delays for part
replacement.
Team IDC recommends that all future teams start this process as early as possible, as this
team loss significant time waiting for it to be finished. It is also recommended that more than one
person knows how to do circuitry, so that if one person makes an error, another person knows
enough to be able to help them out.
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Product Development Review
The hovercraft design project had two major parts: the design, and the
implementation. The design, while it was challenging, was completed on time in accordance to
the milestones. The team did not always complete their own internal deadlines however; it was
discovered that internal deadlines were not sufficiently motivating. The biggest set back with the
design process was discovering that an error had been made in calculating the area of the octagon
shape. Because of this error, it was discovered that the wrong fan had been chosen, and based on
that, the wrong batteries. Fortunately, all these errors were discovered before any parts were
ordered; this would have been quite disastrous. However if the team had checked their work
better, none of this would have happened in the first place.
The second part, implementation, was a bit trickier. The team was able to make the first
milestone, milestone five, in which propulsion, levitation, and basic coding had to be proved
functional, on time, however, milestone six was met a week after deadline. The biggest delay
was not in the actual construction of the hovercraft, but in getting the code to work.
Unfortunately, only two team members had a strong grasp of the code, so the rest of the team
was a bit helpless to aid them. Once code was finally working though, the team was able to meet
the milestones without any problems.
Product Performance
21
While the design did finally work in the end, it was realized that if the design was
different, the final milestones might have been met on time. When the team initially chose to use
one propulsion fan on a servo motor, the team thought it would make things simpler because
having two fans can have issues with one fan being stronger than the other. However, it was
discovered that having a propulsion fan on a servo made coding significantly more difficult
because the servo motor did not always rotate the way the team had initially intended. It took the
team over two weeks to discover that the servo motor moved relative to it’s current position, not
absolutely, and this caused the team to go over deadline on the last milestone.
Overall, the team worked reasonably well together, with no major conflicts. Having an 8
a.m. class did prove to be detrimental, as people were more likely to be grumpier or just not
show up in the morning, which also cost the team time. Unfortunately, not all members took the
project seriously enough to wake up early in the morning and come in ready to work.
Communication was not much of a problem. While initially the group decided to use
Facebook as a means of communication, it was discovered that e-mail was more efficient and
reliable and was checked on a more regular basis.
A big mistake was getting overconfident after making milestone 5 on time. The team got
complacent, without realizing that milestone 6 was coming up soon. As a result, significant time
was lost with people going slow, not coming in on time, and not coming in on the extra Friday
sessions. This team highly encourages future teams to always work as if the deadline is
imminent; it saves a lot of stress in the end.
As to the writing and reporting section of the project, that generally went fine, though the
team definitely learned to proofread multiple times, and by different people. Many mistakes were
made in the initial PDR that could have easily been spotted if the project was finished earlier and
the team had more time to proofread.
Overall, the team learned a lot throughout the design process. Specifically, the team
learned to appreciate Murphy’s Law: if it can go wrong, it will. Many mistakes were made that
might have been fixed if the team had proofread in the first place, but many mistakes were
unavoidable: the trick is to just work to finish the hovercraft as fast as possible so that there is a
maximum amount of time leftover to troubleshoot. In general, the team learned to not become
pessimistic, and to ask for help immediately from people who had more experience than first
22
semester freshman. The team would like to thank Kevin Calabro and Dylan Rebois for all their
assistance.
Bill of Materials
Quantity
Model Number
Description Vendor Unit Price
Total
1 9846 Ultrasonic Sensor Lego1 25.59 25.59
3 9844 Light Sensor Lego 14.39 43.17
1 9841 NXT MotorA.James Clark
School of Engineering
25.00 25.00
1TD8303H Propulsion Fan Vantec USA2 11.99 11.99
1 11-001 FoamRC Foam discount
hobby supplies3 20.00 20.00
1 2637809 Rip-stop NylonJoann’s Craft
Supplies4 6.99 6.99
17.2V-3800-
2-charBatteries
Battery Superstore, via amazon.com5 76.98 76.98
1 LZ23K Grill for Fans EBM PAPST6 1.94 1.94
2 9842 Servo Motors Lego 15.19 30.38
1 2N3904 Circuitry Parts Amazon.com 11.06 11.06
1 3212JH3 Levitation Fan EBM PAPST 61.83 61.83
Total $314.93
1 http://shop.lego.com/product2 http://www.vantecusa.com/front/product/view_detail/114Skirt3 http://rcfoam.com/cart.php?target=product&product_id=634&category_id=824 http://www.joann.com/joann/catalog.jsp?CATID=cat3071&PRODID=xprd5609615 http://www.amazon.com/exec/obidos/tg/detail/- /B001BKPAR6/ref=pd_luc_mri?_encoding=UTF8&m=A3IAN4VN1Q26HU&v=glance6 http://www.ebmpapst.us/allpdfs/tubeaxial_metalguards.pdf
Table 1:Bill of Materials
23
Additional Costs
Table 2: Additional Costs
These additional costs, added onto the Bill of Materials Costs, reflect a total of about $400. Lisa
Liu, a team member, was be in charge of handling all the money and ensuring that the costs were
split evenly throughout the group.
Lessons Learned
The biggest mistake the team made was ordering everything on-line, instead of trying to
find parts at local stores. As a result, a significant amount was paid for shipping, and while the
parts did come on time, if they hadn’t, that would have significantly delayed the project. Also,
the team highly recommends other teams buy extra batteries. One of the batteries the team
ordered arrived broken; but since the team had ordered two batteries, there was no delay in the
project. It is definitely expensive to do things this way, but it is well worth it.
24
Item Cost
Battery Charger 25.00
Total Shipping 54.00
Duct Tape 6.00
Total $85.00
Appendixes
Objects in the Text:
Figure 1: Sensors........................................................................................................................................... 15Figure 2: Main Power Supply Circuit......................................................................................................17Figure 3: Propulsion Fan Circuitry..........................................................................................................18Table 1:Bill of Materials................................................................................................................................ 22Table 2: Additional Costs.............................................................................................................................. 23
Appendix A: Drawings, Figures, Lists and Charts.......................................................................25Table 3: Weight Table.................................................................................................................................... 25Table 4: Item Positions.................................................................................................................................. 26Figure 4: Center of Mass Diagram............................................................................................................26Figure 5 : Skirt Template to be used for Construction...........................................................................27Figure 6: Levitation Fan Pressure and Flowrate................................................................................27Figure 7: Gate Activation Mechanism........................................................................................................28Figure 8: Drawing of Completed Hovercraft............................................................................................29Figure 9: Lower Grooves............................................................................................................................... 30Figure 10: Counter-rotating Grooves.........................................................................................................31Figure 11 : Wiring Schematics..................................................................................................................... 32Table 5 : Position of Hovercraft and Algorithm Response...................................................................33Figure 12: Top and bottom of finished circuit.....................................................................................33Full Code........................................................................................................................................................... 34
Appendix B: Meeting Minutes.......................................................................................................... 38
Appendix C: Construction Details................................................................................................... 40Figure 13 : Picture of Levitation Fan cutout and Cardboard lower deck with skirt attached......41Figure 14: Levitation Fan Picture with Grill Attached..........................................................................42Figure 15: Counterrotating Fins..................................................................................................................43Figure 16: Propulsion Fan Mounted on Servo.....................................................................................44Figure 17: Three Light Sensors and one Ultrasonic Sensor..................................................................45Figure 18: Arm Drawing............................................................................................................................... 46
Appendix D: Gantt Chart.................................................................................................................. 47
25
Appendix A: Drawings, Figures, Lists and Charts
Table 3: Weight Table
Part Mass (grams)
NXT w/ 6 Alkaline Batteries 303
NXT Ultrasonic Sensor 24
NXT Servo Motor 83
Battery Pack 376
5 20” Cables 70
2 15” Cables 30
Light Sensors + Housing 70
Structure 154
Arm Unit 105
Levitation Fan 281
Propulsion Fan Unit 180
Total 1676
26
Table 4: Item Positions
1
2
5
4
3
6
Figure 4: Center of Mass Diagram
27
Item Weight
x-coordinate (inches) y-coordinate (inches)
#
Propulsion Fan System 262.5g 0 in. 5.5 in. 1Batteries 376g 2 in. -7 in. 2NXT 303g -5.5 in. 2.13 in. 3Sensor Unit 94g 0 in. 12 in. 4Arm 104g 3.6 in. 4 in. 5Levitation Fan 281.2g 0 0 6Combined Structure 154g 0 in. 0 in. 7
Figure 5 : Skirt Template to be used for Construction
EBM PAPST Fan7 (See Curve 4)
7
Flowrate is 91.1CFM, pressure required is 94.8 Pa
Figure 6: Levitation Fan Pressure and Flowrate
28
Figure 7: Gate Activation Mechanism
29
Figure 8: Drawing of Completed Hovercraft
30
31
Figure 9: Lower Grooves
32
Figure 10: Counter-rotating Grooves
33
Figure 11 : Wiring Schematics
34
35
Figure 12: Top and bottom of finished circuit
36
37
Table 5 : Position of Hovercraft and Algorithm Response
38
Part 1: Before the Gate
W W W Go straight
W W B Turn left
W B W Continue turning
W B B Turn hard left
B W W Turn right
B W B Continue turning
B B W Turn hard right
B B B Go straight
Part 2: After the Gate
W W W Continue turning
W W B Turn right
W B W Go straight
W B B Turn hard right
B W W Turn left
B W B ---
B B W Turn hard left
B B B Go straight
Full Code
#pragma config(Sensor, S1, LR, sensorLightActive)#pragma config(Sensor, S2, LM, sensorLightActive)#pragma config(Sensor, S3, LL, sensorLightActive)#pragma config(Sensor, S4, SS, sensorSONAR)#pragma config(Motor, motorA, SM, tmotorNormal, PIDControl, )#pragma config(Motor, motorB, AM, tmotorNormal, PIDControl, )#pragma config(Motor, motorC, Fan, tmotorNormal, PIDControl, )//*!!Code automatically generated by 'ROBOTC' configuration wizard !!*//
#define LIGHT_DARK 40#define SOUND_FAR 10#define FAN_ARM_SPEED 50#define ARM_SPEED 20#define INTERVAL 20#define DEFAULT_SPEED 30#define RETURN_SPEED 40#define WINDOW 10int flag = 1;
void SetFan(int angle) { nxtDisplayTextLine(7,"Angle: %i", nMotorEncoder[motorA]); if (abs(nMotorEncoder[motorA]) >= abs(angle) && !(nMotorEncoder[motorA] / abs(nMotorEncoder[motorA]) == angle / abs(angle))) { // Inside window motor[motorA] = 0; nxtDisplayTextLine(6,"On right track"); } else { nMotorEncoderTarget[motorA] = abs(angle - nMotorEncoder[motorA]);//-nMotorEncoder[motorA] + angle * flag; nxtDisplayTextLine(6,"Turn angle: %i", nMotorEncoderTarget[motorA]); if (angle < flag * nMotorEncoder[motorA]) {//if (angle < 0) {//if (angle < nMotorEncoder[motorA]) { nxtDisplayTextLine(5,"Turn right."); motor[motorA] = FAN_ARM_SPEED; } if (angle > flag * nMotorEncoder[motorA]) {//if (angle > 0) {//if (angle > nMotorEncoder[motorA]) { nxtDisplayTextLine(5,"Turn left."); motor[motorA] = -FAN_ARM_SPEED; } } if(angle == 0) { nMotorEncoderTarget[motorA] =nMotorEncoder[motorA];//-nMotorEncoder[motorA] + angle * flag;
39
nxtDisplayTextLine(6,"Turn angle: %i", nMotorEncoderTarget[motorA]); if (angle < flag * nMotorEncoder[motorA]) {//if (angle < 0) {//if (angle < nMotorEncoder[motorA]) { nxtDisplayTextLine(5,"Turn right."); motor[motorA] = FAN_ARM_SPEED; } if (angle > flag * nMotorEncoder[motorA]) {//if (angle > 0) {//if (angle > nMotorEncoder[motorA]) { nxtDisplayTextLine(5,"Turn left."); motor[motorA] = -FAN_ARM_SPEED; } }}
task main() {int lightA, lightB, lightC;int soundA;nMotorEncoder[motorA] = 0;nMotorEncoder[AM] = 0;wait10Msec(5);
//int count;//motor[Fan] = DEFAULT_SPEED;//nMotorEncoderTarget[AM] = 45;//motor[AM] = 45;
// Part 1: Find the Gateint step = 1;int prev = 0;
for (;;) {lightA = SensorValue(LR);lightB = SensorValue(LM);lightC = SensorValue(LL);
prev = soundA; soundA = SensorValue(SS); nxtDisplayTextLine(0, "r %i", lightA);
nxtDisplayTextLine(1, "m %i", lightB);nxtDisplayTextLine(2, "l %i", lightC);nxtDisplayTextLine(3, "sound: %i", soundA);nxtDisplayTextLine(4, "prev: %i", prev);if (nMotorEncoder[AM] > 80)
motor[AM] = -ARM_SPEED; else if (nMotorEncoder[AM] <= 0) motor[AM] = ARM_SPEED;
nxtDisplayTextLine(5, "arm motor: %i", nMotorEncoder[AM]);
40
if (lightB < LIGHT_DARK) {motor[motorC] = DEFAULT_SPEED;SetFan(0);flag = 1;if (lightA > LIGHT_DARK == lightC > LIGHT_DARK) {
} else { /*if(lightA < LIGHT_DARK && lightC < LIGHT_DARK) { } */ if (lightA < LIGHT_DARK) {
SetFan(-30); } if (lightC < LIGHT_DARK) { SetFan(30); } } } else { motor[motorC] = RETURN_SPEED; if (lightA < LIGHT_DARK) { SetFan(-30); } if (lightC < LIGHT_DARK) { SetFan(30); } } flag = -1; if (soundA < SOUND_FAR) { nMotorEncoderTarget[AM] = 25; motor[AM] = -10; break; } /* if(soundA < SOUND_FAR || soundA == 255) { if (soundA > prev + 12) { nxtDisplayTextLine(5, "arm motor: %i", nMotorEncoder[AM]); nMotorEncoderTarget[AM] = abs(90 - nMotorEncoder[AM]); motor[AM] = -10; break; } } */ wait1Msec(INTERVAL); }
41
// Part 2: Stay on Line SetFan(0); flag = 1;
for (;;) {lightA = SensorValue(S1);lightB = SensorValue(S2);lightC = SensorValue(S3);nxtDisplayTextLine(1, "r %i", lightA);nxtDisplayTextLine(2, "m %i", lightB);nxtDisplayTextLine(3, "l %i", lightC);
//less than LIGHT_DARK means sensor sees black tapeif (lightB < LIGHT_DARK) {
motor[motorC] = DEFAULT_SPEED;SetFan(0);flag = 1;if (lightA > LIGHT_DARK == lightC > LIGHT_DARK) {
} else { /*if(lightA < LIGHT_DARK && lightC < LIGHT_DARK) { } */ if (lightA < LIGHT_DARK) {
SetFan(-25); } if (lightC < LIGHT_DARK) { SetFan(25); } } } else { motor[motorC] = RETURN_SPEED; if (lightA < LIGHT_DARK) { SetFan(-25); } if (lightC < LIGHT_DARK) { SetFan(25); } } flag = -1; wait1Msec(INTERVAL); nxtDisplayTextLine(6,"motorA is %i ", motor[motorA]); //wait1Msec(INTERVAL); } }
42
43
Appendix B: Meeting MinutesMeeting 1: September 7th, 2009, in Ellicott Hall. Full Team Meeting. 90 minutes.
Absent: Daniel Silversmith Discussed:
o Shape of Hovercraft: Circle, simple to cut and calculate area foro Size of Hovercraft: 2ft, large enough to hold everything but still had room to
maneuver on tracko Types of fan: Justin had spare axial fans, try to make those worko Different parts/Weights: Styrofoam for body of hovercraft: cheap, easy to cut,
lightweight. Soft skirt to maximize friction. Two fans to steer.o Thoughts for arm: touch sensor could indicate when hovercraft hits all and needs
to lift the armo Subteam assignments, subteam captains decided on as Rachel, Daniel, and
William. Action Items:
o Levitation Team: Research Fanso Structure Team: Think more about the arm, and about specific materialso Control Team: Research sensor costs
Meeting 2: September 14th, 2009, in Ellicott Hall. Full Team Meeting. 90 minutes. Absent: Mark Weniger, Lisa Liu Discussed:
o Changed shape of hovercraft to octagon on Mr. Calabro’s advice that straight lines are easier to work with when using a skirt
o Discussed arm ideas, sensors, skirt material Action Items-Assigned Tasks for presentation:
Justin: Gantt Chart. Derek: Excel Chart Lisa: Research power information (Ni-Cd batteries) Lekan: Styrofoam weight, cost Will: chart of four possible axial fans (in case Justin’s doesn’t work) Omar: Sketch of basic shape and size of hovercraft Rachel: Skirt material (Rip-stop nylon). Find out weight, costs Mark: Arm: present two ideas, either a flexible stick or a wooden arm
attached to rubber bands. Daniel: Sensor write up: light sensors from lego, attached onto front of
hovercraft Julianna: powerpoint
Meeting 3: September 21st, 2009, in Ellicott Hall. Full Team Meeting. 90 minutes Absent: Derek Dechent, Omar Khan, Lekan Solarin Finished Gantt Chart Practiced Presentation (Julianna, Lisa, Justin) Action Items:
o Levitation Fan: Narrow down fan choices to oneo Structure team: narrow down skirt choices to one
44
o Control Team: Start working on pseudocodeMeeting 4: September 28th, 2009, in Ellicott Hall. Full Team Meeting. 90 minutes.
Absent: Rachel Fan, Lekan Solarin Broke up tasks for next milestone
o Structure Team assigned to finalize weightso Control Team assigned to finalize sensorso Levitation Team assigned to pick out fan.
Meeting 4.3: September 30th, 2009, in Ellicott Hall. Structure Team Meeting. 60 minutes. Members Present: Rachel, Lekan, Lisa Discussed weight and cost of batteries and styrofoam
Meeting 4.6: October 1st, 2009, in Cambridge Hall. Control Team Meeting. 45 minutes. Members present: Daniel, Omar, Justin Discussed: Weights and costs of NXT, servo motor for arm, cables, and sensors
Meeting 4.9: October 3rd, 2009, in Chestertown Hall. Levitation Team Meeting. 60 minutes. Members present: William, Derek, Mark Discussed: Based on weights the other groups sent, and area calculations, a fan was
decided on. It was decided that Justin’s fan could work for levitation and for propulsion, but only if one propulsion fan on a servo was used. This alteration was made to the final design.
Meeting 5: October5th, 2009, in Queen Anne’s Hall. Team Leaders Meeting. 180 minutes. Members present: Julianna, William, Rachel, Daniel Discussed
o Finalized arm design to a servo motor lowering and raising an arm, after deciding a passive system was too complicated
o Calculated center of mass of hovercrafto Decided who would present: Daniel, William, and Derek.o Went over pricing to ensure under budget. o Subteam leaders went over the progress they made towards the PDR.
Action Itemso Structure team to buy skirt materialo Structure team to start working on drawingso Control team to finish pseudocodeo Levitation fan to finish typing up propulsion information.
Meeting 5.5: October 10thth, 2009, in Chestertown. Levitation Team Meeting. 60 minutes. Members present: William, Mark, Derek Discussed: A gross error was discovered in the calculations of error. Justin’s levitation
fan would not work, and the new fan needed to lift hovercraft would require a larger battery output than could be provided by Ni-Cd batteries, informed Structure and Power Team of this.
Action Itemso Started trying to find a new fan that would work with the new flowrate and
pressure requirements.Meeting 6: October 16th, 2009, in Engineering Library. Full Team Meeting. 120 minutes.
Members Absent: Lekan, Derek, Omar
45
Discussed: o How to get enough power to a fan without increasing the weight so much that the
hovercraft would lift. Discussed changing shape to alter area, but eventually decided on using Li-ion batteries, that are more expensive but significantly lighter.
Action Itemso Decided on fan ordered levitation fan, Styrofoam, sensors, and Li-ion batteries.
Rachel would pick up skirt material that week.
Meeting 7: October 18th, 2009, in Ellicott Hall and Glenn L. Martin Computer Lab. Full Team Meeting. 420 minutes.
Members Absent: Justin, Lekan Finished FDR:
o Worked together as a team to finalize engineering drawingso Practiced the PDR presentation, proofread PDR and PDPP.
Appendix C: Construction Details
See Figure 4: Center of Mass Diagram for specific item placement.
1. Build Octagon Base and Lower Base
2. Cut out hole for levitation fan
3. Build counter-rotating fins; attach two bases
4. Build base for propulsion fan
5. Attach Sensor Unit
6. Attach Arm
1: Build Octagon Base and Lower Base
See Figure 13 : Picture of Levitation Fan cutout and Cardboard lower deck with skirt attached
White EPP Styrofoam Upper Deck - 457mm side to side; 495mm vertex to vertex
1. Mark out a center point and mark out 45˚ angle intervals around the point to create a
regular octagon.
2. Draw a 495mm line with the 248mm mark at the center point through opposite 45˚ angle
marks.
3. Repeat this process for all 4 lines to mark out the endpoints of the octagon sides.
4. Connect the endpoints to form the 8 congruent sides of 188mm.
5. Using a wire cutter, cut out the Styrofoam octagon for the upper deck.
46
Cardboard Lower Deck – 406mm side to side; 439mm vertex to vertex
1. Mark out a center point and mark out 45˚ angle intervals around the point to create a
regular octagon.
2. Draw a 439mm line with the 220mm mark at the center point through opposite 45˚ angle
marks.
3. Repeat this process for all 4 lines to mark out the endpoints of the octagon sides.
4. Connect the endpoints to form the 8 congruent sides of 168mm.
5. Using a box cutter, cut out the cardboard octagon for the lower deck.
6. Cut our four holes the let air escape in the corners of the cardboard.
Figure 13 : Picture of Levitation Fan cutout and Cardboard lower deck with skirt attached
2: Cut out hole for levitation fan
See Figure 14: Levitation Fan Picture with Grill Attached
Fan cut out:
1. There should be a mark made in the center point of the upper deck from the previous
construction steps.
2. Line up the center of the fan and the center of the base and trace the outline of the fan
onto the base
3. Choose a circular drill bit that most nearly fits the size of the drawn square, while
remaining completely inside the square, and attach it to the drill press
4. Use the newly attached drill bit to cut out a circular hole completely through the main,
two inch thick Styrofoam base.
5. Use a box cutter and follow the traced out square on the base, creating 4 10 mm deep
triangular notches with the same dimensions of that on the fan that the fan can rest in.
6. Place the levitation fan in the hole. This does not need to be glued down.
47
7. Glue on the grill onto the levitation fan.
8. See the picture of the levitation fancut out in this Appendix A.
Figure 14: Levitation Fan Picture with Grill Attached
3: Build counter-rotating fins; attach two bases
See Figure 10: Counter-rotating Grooves
1. At the center of the craft, a circle should be marked out with a diameter of 92mm. That is
the same diameter of the levitation fan so the grooves do not interfere with the spinning
of the fan.
2. There should be eight lines radiating from the center from the construction of the base
piece, they should all be heading into one of the corners of the octagon. If they are not
there, they should be drawn.
3. Trace a 25.4mm from the circle outward along one of the lines to the corners.
4. From the outward end of the last line, make a 35 degree angle in the counter-clockwise
direction and draw a line that is 110 mm long.
5. Continuing from that line, make a 30 degree angle again in the counter-clockwise
direction and draw a line that is 45 mm in length.
6. Using a hot wire, carve out three foam rectangles with the dimensions
12.7mmX12.7mmX25.4mm.
7. Hot glue the three foam supports with a square face down tangent to the middles of the
three lines that were drawn in steps 3-5.
48
8. Cut out a strip of cardboard that is 180mmX25.4mm. Curl the cardboard so that it will be
easier to make into a curve.
9. Place hot glue on the face of the three supports tangent to the lines and place the
cardboard with a long side along the lines and press the back of it against the supports.
Run hot glue along where the cardboard of the turning fin meets the cardboard of the base
to keep it in place.
10. Repeat steps 3-9 3 more times, each time starting 90 degrees or 2 radiating lines along the
circle from the last one. A final picture of the fins can be found in Appendix A.
11. Glue the lower base to the upper base by hot gluing the foam supports to the bottom of
the upper deck.
Figure 15: Counterrotating Fins
4: Build base for propulsion fan.
1. The fan is mounted on a servomotor that is attached to the foam base.
2. Before starting, glue on the grill for the propulsion fan.
49
3. Cut out the base, a rectangle of foam with a piece of cardboard glued on top. The
rectangle is 115mm long and 35mm wide and 15mm high. The cardboard, cut 115mm x
35mm, is hot glued to the top of
the rectangle of foam.
4. This piece is then taped to the
servomotor and the whole
attachment was glued to the
base.
5. Make another Styrofoam block
with a side of cardboard, this
time, to the same dimensions of
the bottom of the propulsion
fan.
6. Glue this block onto the bottom of the propulsion fan.
7. Acquire two thin Lego connector pieces that fit into the servomotor.
8. Cut out two small holes into the propulsion fan’s Styrofoam + cardboard.
9. Connect the propulsion fan to the servomotor using the two small Lego connectors. For
additional stability, tape the propulsion fan to the bottom of the servo motor using duct
tape.
5: Attach Sensor Unit
Light Sensors
1. The light sensors are attached to three L-shaped pieces cut out of white EPP foam.
2. The pieces are 145mm long and hang down 105mm. They are 50mm wide and 30mm
thick.
3. These pieces were cut using the hot wire.
4. A rectangular indent 7mm by 20mm and 5 mm deep was cut out in each of the three
pieces.
5. The center of this indent is 20 mm form each side and 25mm from the bottom of the
piece.
6. The light sensor was placed in the indent and secured with duct tape.
Figure 16: Propulsion Fan Mounted on Servo
50
7. These pieces were then glued to the craft using hot glue. They were placed 30mm apart.
65mm of the piece was attached to the craft and the other 80mm is hanging off of the
front.
8. The middle piece was altered and it is only 20mm high instead of 30mm to give the fan
proper clearance.
Figure 17: Three Light Sensors and one Ultrasonic Sensor
Ultrasonic sensor
1. The ultrasonic sensor was attached to a piece of white EPP foam, and this piece of foam
also serves the purpose of blocking out external light
2. This piece is a rectangle with four protrusions that fit in the spaces between the light
sensor attachments.
3. The rectangle part of the piece is 268mm long and 57mm wide and 25mm thick.
4. There are four protrusions and they are each 41mm long rectangles and vary in width.
From left to right the widths are 18mm, 31mm, 31mm, and 38mm.
5. The ultrasonic sensor is attached to the underside using hot glue and duct tape.
6. There is a 50 mm gap between each protrusion and it was placed in between the pieces
that hold the light sensors and was kept in place with hot glue.
6: Attach Arm Unit
The wire cutter needs to be used to cut two Styrofoam pieces, a base for the arm
structure, and a piece that will actually push the button
51
For the first piece, cut a rectangular prism with dimensions 175mmx90mmx50mm. From
the top view, cut a 50mm long, 50mm wide, 15mm deep prism out.
For the second piece, cut an L shape that is 50 mm deep with leg dimensions 80mm long,
30mm wide and 95mm long, 45mm wide
Using a box cutter, cut a 50mm by 50mm square out of cardboard. Use a hot glue gun to
attach this to the outside of the 95mm leg, making sure that the square is flush with the
edge of the leg that is not the vertex of the two legs
Create two small holes about 10 mm deep that are centered in the cardboard and are 10
mm apart.
Use a hot glue gun and a 50mm rod into the hole nearest the top of leg, and a 35mm rod
into the other.
Glue the other end into a servo motor, ensuring that the longer rod runs through the
middle hole in the servo so that it can control the rotation of the L shaped piece.
Glue the entire piece onto the hovercraft, 13mm to the left of the propulsion fan base.
Figure 18: Arm Drawing
52
Appendix D: Gantt Chart
53
54
55
