8 Team Members Contributions to the Projects ………………………
8.1 Stephen Elovetsky ………………………………………………
8.2 Steven Rogers ………………………………………………
9 Conclusion ………………………………………………………………
10 References ………………………………………………………………
11 Acknowledgments ………………………………………………………
12 Appendix ………………………………………………………………
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Abstract
All-terrain and beach wheelchairs are becoming more popular and more common,
however, they are still too expensive for many people and families to purchase. Annalee Hughes
and Nathan Lamb are both very adventurous children who would benefit greatly from all-terrain
power chairs, and Danielle Giroux is a very social young girl that would benefit from an easy to
maneuver beach wheelchair. Over the course of the year, our team is working on modifying all-
terrain power chairs that were built for Annalee and Nathan by previous senior design teams. We
are also working on designing and building a beach wheelchair for Danielle that is a
modification of an old, collapsible stroller that she had when she was younger.
The all-terrain power chair that is being redesigned for Annalee features an automated
self-leveling system for the seat of the chair. Controlled by a microcontroller, the system reads
tilt data from accelerometers placed on the chassis of the chair and on the seat and controls a
linear actuator mounted beneath the seat. The actuator tilts the seat back when the chair is
traveling downhill and tilts the seat forward when the chair is traveling uphill. The system also
sounds a buzzer if the chair is traveling on a slope of an angle greater than 10°. With these
features, the chair is capable of giving the client freedom of movement on many terrain areas
while also keeping her safe.
The all-terrain wheelchair that is being redesigned for Nathan features improved steering
and handling, and improved joystick. The front suspension of the chair is being replaced with
caster style wheels giving it superior turning capabilities over the previous design. The joystick
is being replaced with a more robust one that will last the lifetime of the chair and will be
mounted to new armrests on the seat that will provide improved comfort of use for the client.
The all-terrain wheelchair will give Nathan the freedom of movement that he has not had before,
allowing him to enjoy more outdoor activities with his family and friends.
The beach wheelchair the is being designed for Danielle features a wide base and easy
turning, as well as the ability to collapse and be disassembled partially for easy transportation
and storage. The chair will ride on four large polyurethane balloon tires that will allow it to move
across the sand easily. The casters are moved from the front of the chair to the back to make
pushing and turning the chair much easier. When it comes time to move the chair to or from the
beach, it will collapse to a manageable size making it much easier to transport and also to store
in the Winter months. The beach chair will provide Danielle and her family a much easier means
of moving around on the sand, allowing them to spend more time enjoying their vacations and
day trips to the beach.
3
1 Introduction
1.1 Background
1.1.1 Annalee Annalee is an eleven-year-old girl with cerebral palsy. Cerebral palsy is a condition that
usually involves brain and nervous system functions. Cerebral palsy is caused by injuries or
abnormalities in the brain and symptoms of the condition vary from individual to individual [1].
In the case of Annalee her cerebral palsy has resulted in underdeveloped muscles in her legs and
upper body. The lack of proper stimulation of the muscles by the brain and nervous system has
resulted in their being relatively weak and underdeveloped, meaning that Annalee cannot stand
up and support her own weight by herself.
Annalee is very adventurous and wants to be independent in what she does. She
thoroughly enjoys exploring her spacious, three-acre backyard. Her family has a barn, pond, and
blueberry bushes that she enjoys visiting and exploring. The problem is that the family’s
backyard is not flat, but instead very hilly and rocky. Due to her cerebral palsy, Annalee uses a
power chair to move around, controlling it via a joystick with her right hand, however it is not
capable of safely traversing the terrain in her backyard. Previously, she has tipped over her
power chair while trying to use it in the backyard and because she is not very strong, she cannot
right the chair or herself when this happens.
Two years ago, an all-terrain power chair was built for Annalee by a group in Senior
Design. The chair was designed to auto-level the seat so that Annalee could use it to safely
traverse her family’s property. When Annalee first received the chair, it worked as expected.
After a month or two, however, it began to malfunction and the auto-leveling system stopped working all together. The brakes on the chair were also not working properly, resulting in a very
long stopping distance. Our goal is to remedy both of these issues so that Annalee can use the
chair to safely explore her backyard.
1.1.2 Nathan Nathan is a twelve-year-old boy with myelomeningocele and an autism spectrum
disorder. Myelomeningocele is a form of spina bifida. Myelomeningocele is a birth defect in
which the spinal canal and backbone do not fuse properly [2]. In Nathan’s case, the
myelomeningocele caused partial paralysis of the legs, thus resulting in weakness in the muscles
in his hips, legs, and feet. The myelomeningocele also caused hydrocephalus, which is a buildup
of fluid in the brain. Nathan underwent surgery to drain the fluid built up in the brain into his
bladder, where it could be excreted by the body naturally. Nathan also has weak trunk strength,
which results in an abnormal, slanted sitting posture. As mentioned by his parents, this may be
causing Nathan to develop scoliosis. Along with his physical disabilities, Nathan has an autism
spectrum disorder. Autism is a developmental disability that causes problems or difficulties in
social interaction and communication. Autism is called a “spectrum” disorder because it is a
group of disorders with similar symptoms and symptoms can range from mild to severe [3].
Like any child his age, Nathan enjoys participating in outdoor activities with his family
and friends. Due to his myelomeningocele, Nathan relies on a manual wheelchair, pushed by
someone else, to move around. His family is in the process of trying to get a power chair for him
to use around their home and at his school. Nathan is unable to move around and interact with
people and his surroundings as independently as he could.
4
Last year, a Senior Design team designed and built an all-terrain wheelchair that would
allow Nathan to traverse the terrain around his house and other outdoor areas freely and
independently. Nathan is proficient with his right hand, therefore the chair is controlled with a
joystick mounted on the right side of the chair. When the chair was given to Nathan, it did not
work properly. The movement of the chair did not correspond to the direction that the joystick
was moved in. Along with that, when the chair turned it would jump and jitter until it stopped
moving. Both of the factors made it very unsafe for Nathan to use. Our goal is to determine the
cause of the problems and redesign parts of the chair in order to make it safe for Nathan to use.
1.1.3 Danielle Danielle is an eleven-year-old girl with cerebral palsy. Similarly to Annalee, Danielle’s
cerebral palsy has caused her lower body, especially her leg muscles, to become underdeveloped
and unable to support her standing and walking. Danielle is very friendly and social. She loves
spending time with her family and friends and really enjoys trips and vacations to the beach.
Danielle currently uses a power chair to move around her home and school. The chair,
however, is not designed to travel on uneven, off-road terrain. This means that when the family
goes to the beach or other outdoor activities, Danielle usually cannot use her power chair and
thus relies on others to mover her around in a manual one. Her family rents or borrows beach
wheelchairs when they visit beaches, but these chairs are difficult to move and the rental fees add
up, making it more difficult to go to the beach as often as they may like. Our goal is to design
and build a collapsible and easy to maneuver wheel chair that will make the family’s trips to the
beach less difficult and more enjoyable for everyone.
1.2 Purpose of the Projects
1.2.1 Annalee The goal of the project for Annalee is to fix the low center of gravity power chair that
was built for her two years ago. It was originally designed with an auto tilt correction mechanism
built into the seat of the chair. It was supposed to keep Annalee level, giving the chair more
balance as it traversed the hills and rocks in her family’s yard. This anti-tilt mechanism and the
braking system of the power chair are not working correctly, making the chair unsafe for
Annalee to use on her own. The team needs to analyze the mechanical and electrical systems of
the power chair to determine what is causing the malfunction and correct any issues that are
found.
1.2.2 Nathan The goal of the project for Nathan is to fix the all-terrain power chair that was built for
him last year. It was designed to allow Nathan to traverse his yard, the beach, and other rough
terrain on his own. It was built with four-wheel drive to make it more efficient and capable of
traversing the varying terrain types that he would encounter. When the chair was completed,
there was little time to test all of the mechanisms of the chair and when Nathan tried to first use
it, his parents noticed that the chair did not respond properly to the movement of the joystick.
Nathan was unable to use the chair after that because it was not safe for him to operate on his
own. The joystick was also very small and not very strong. Nathan’s parents said that Nathan has
a tendency to be more forceful with things because he doesn’t understand that he is damaging
them. They asked that the joystick be upgraded to one that was more robust and would withstand
the more aggressive treatment that Nathan would give it. The team needs to analyze the electrical
5
systems and programming to determine what is causing the power chair to malfunction and make
the appropriate changes to make it safe for Nathan to use. In doing this, the joystick will be
replaced with a new, more robust, joystick that will last the lifetime of the chair. The seat of the
chair also has to be modified slightly to better accommodate Nathan’s growth and to provide the
most comfortable environment for him to use his chair in.
1.2.3 Danielle The goal of the project for Danielle is to make her movement easier on the uneven terrain
at the beach. The beach wheelchair that we will build is going to be designed to allow Danielle’s
parents to easily move Danielle over the sand when they go to the beach. Traditional manual
wheelchairs have very thin wheels that do not move across the sand, but rather cut into it,
making them impossible to use at the beach. The beach wheelchairs that the family usually rent
when they go to the beach are also not easy to move through the sand. The wheelchair that we
design will move across the sand with the least amount of effort possible, allowing Danielle and
her family to spend more time enjoying the beach and less time trying to get there.
1.3 Previous Work
1.3.1 Products All-terrain power chairs are becoming more popular, however, they are generally very
expensive. PlanetMobility.com features a number of all-terrain power chairs with a range of
features. One such power chair is their Viking 4x4, which features four-wheel drive and a self-
leveling seating system. The Viking 4x4 is capable of traversing sand, mud, snow, and other
rough terrain with ease. The gyroscopic self-leveling seating system allows the power chair to
climb hills, ramps, and stairs at an angle of up to 36°. Another all-terrain power chair featured on
PlanetMobility.com is the X5-Frontier. The X5-Frontier is a mid-wheel drive all-terrain power
chair. Unlike the four-wheel drive power chairs, the mid-wheel drive chair drives off of only two
wheels at the center of the length of the chair and has four smaller support wheels at each corner.
This setup is less stable in general making it inadequate for off-road use, though the X5-Frontier
claims to be comparable to the 4x4 chairs on most terrain. While both of these power chairs are
very powerful and capable of handling all types of terrain, they come with a hefty price tag. Both
the Viking 4x4 and X5-Frontier have base prices of nearly $10,000. With many of the available
options, the price of either chair could easily increase by hundreds or thousands of dollars,
making them even more expensive for the family to purchase.
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Beach wheelchairs are also becoming very popular and in demand. Persons that need a
wheelchair to move around used to never be able to go to the beach because it is near impossible
to push a standard wheelchair across the sand. Beach wheelchairs use polyurethane or PVC
wheels to easily traverse even the softest sand. They allow disabled people and their families to
enjoy the beach without having to worry about how to get there.
Figure 1: Three Viking 4x4 all-terrain power
chairs demonstrating the power chairs ability to
climb steep inclines while keeping the rider
level. Figure 2: The X5-Frontier all-terrain power chair
with mid-wheel drive.
Figure 3: A De-Bug beach wheelchair from Deming
Designs, Inc.
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1.3.2 Patent Search Results In 1998, Adolph Hammer filed a patent for a self-propelled all-terrain vehicle designed
for paraplegics. It used two track mechanisms in place of wheels and was powered by an internal
combustion engine. The seat of the vehicle moved horizontal towards the front of the vehicle to
decrease the distance needed for a person to move between their wheelchair and the powered
vehicle.
In 1995, Micheal Deming filed a patent for an all-terrain wheelchair. It had large, wide
wheels that allowed for easy maneuvering over sand and other similar terrain. The rear wheels
swivel and pivot to allow for easy turning and greater stability over uneven terrain, which is
common on beaches.
1.4 Map of the Rest of the Report Throughout the rest of this report, we will go into more detail about the process by which
we designed each project. We will give a more detailed objective for each of the projects as well
as a list of the subunits of each project as we plan to implement them. Following that we will
discuss some of the constraints that we are working with and any safety issues that are taken into
consideration for each of the projects individually as well as a whole. The impact of the solutions
on the engineering community and new skills that we have learned throughout the process will
be discussed, followed by an updated budget and timeline for the projects. The contributions of
each team member will be discussed, followed by a brief conclusion.
2 Project Design
2.1 Introduction In the following sections, we will describe the planning and brainstorming that went into
picking our optimal design for each project. For Annalee and Nathan’s projects, we were
modifying past projects (Spring 2010, Team 2 & Spring 2011, Team 10, respectively) so that
they would function properly and more safely so rather than alternate designs we state the game
plan that we are following. For Danielle’s chair, we came up with three different alternative
designs, each with their own unique features.
Following the alternative designs, we go into detail about the individual subunits of the
optimal designs for each project. The mechanical, electrical, and software related aspects of each
design are outlined and broken down into the individual components that make each chair work.
2.1.1 Alternative Designs
2.1.1.1 Annalee The power chair that was built for Annalee had a built in, actuator controlled seat tilt. An
accelerometer and a microcontroller chip were used to automate the operation of the actuator in
order to keep the seat level at all times without the need to manually adjust the actuator. The
microprocessor chip and other electrical components were soldered to a generic breadboard. This
breadboard will be replaced with a newly designed printed circuit board, or PCB. In designing
the PCB, we will be able to test the circuit and any changes we make to it to ensure that it
functions the way we need it to. Once it is tested, the board will be printed and used in the chair,
making the wiring much neater and more reliable. The microprocessor chip will then have to be
8
reprogramed in order to compensate for any changes in the circuitry and to ensure that the seat
can auto-level itself.
The accelerometer senses the change in tilt and outputs a voltage that is related to the tilt.
Based on this relationship, the microcontroller will know exactly how much tilt the chair is
experiencing. It will then be able to send the appropriate signal to the actuator to correct the tilt
of the seat. A switch will also be incorporated to allow the user to turn off the automatic leveling
and manually adjust the seat’s tilt.
2.1.1.2 Nathan The power chair that was built for Nathan was not completed, resulting in the chair not
functioning properly. A microcontroller was never implemented in the system but will be now so
that the chair can function properly. The microcontroller will be programed to analyze the input
from a new joystick, and send the appropriate signals to the motor driver that is on the chair now.
All electronic circuitry will be designed and tested using Multisim. PCBs will be created to allow
the wiring to be clean and neat, while allowing the circuitry to function more reliably.
The kill switch for the electric motors will be mounted in an easily accessible location so
that if the chair malfunctions or Nathan loses control of the chair, someone can easily cut power
to the motors and stop the chair safely.
The joystick will be replaced with a more robust one that will last longer and be able to
stand up to more aggressive use from Nathan. The Plexiglas housing that was created for the
battery and other electronic components will be rebuilt with more sturdy material so that it will
not break.
2.1.1.3 Danielle
Alternate Design 1
This design for the beach wheelchair is a three-wheeled, low riding chair. The frame will
be made out of aluminum round stock to ensure that it is light but also strong. The three wheels
will be polyurethane balloon wheels that allow the chair to move easily across the sand. The rear
wheels will be larger and the front wheel will be smaller. The seat will be positioned in between
the rear wheels, slightly reclined so that Danielle can sit back and have her legs extended along
the length of the frame while still being comfortable. The three wheels will be fixed, and the
handle bar will be at an angle that allows for the person pushing the chair to easily lift the front
tire off the ground and turn the chair when pushing down on the handle bar.
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Figure 4: Solidworks three dimensional layout of the three wheel beach wheelchair.
Alternate Design 2
A more traditional looking wheelchair was used as the template for this beach wheelchair
design. This chair, like typical wheelchairs, has a seat with a back and armrests that is on a frame
consisting of four wheels. The overall chair frame will be made out of hallow aluminum bars to
ensure both stability and be lightweight. Two different sizes of polyurethane balloon tires were
used in this construction. The rear wheels are smaller than the forward ones because they are
each part of a castor that rotates freely on an axle. The advantage of putting rotating tires in the
back rather than the traditional front is to allow better ease and maneuverability for the one
pushing the chair by the handlebar because torque is being applied further from the point of
rotation. All four of these tires must have a wide base in order to move easily across the sand and
not sink and get stuck in the process. A headrest has been included for Danielle’s comfort and
safety as she moves across uneven and bumpy terrain. It is important to point out that the seat
must be positioned low to the ground as to have a low center of gravity so that it will not tip as
easily going across the uneven sand.
10
Figure 5: Solidworks three dimensional layout of the four wheel, modular beach wheelchair design.
This beach wheelchair has been designed to disassemble for the purpose of easy storage
and transportation to and from the beach. The seat of the chair has four bolts that protrude
through the frame and are secured using wing nuts so it can be disassembled without the use of
additional tools. The forward tires use the same concept; they are held onto the axle by wing nuts
that can be easily removed. The rear wheel castors are also held into place on the frame by bolts
and wing nuts. This disassembly will allow easy stacking in a van trunk or storage closet.
Alternate Design 3
This wheelchair design is going to be a modification of one of Danielle’s existing
strollers from when she was younger and doesn’t use anymore. The frame and design are sound
for this project. Essentially the main things to change on the stroller to make to a functional
beach wheelchair are to modify the seat and tires. The seat is obviously too small for Danielle
since she has grown, so a new wheelchair seat must be either built or modified from another
wheelchair so that she can sit comfortably. As mentioned before, it is important to point out that
the seat must be positioned low to the ground as to have a low center of gravity so that it will not
tip as easily going across the uneven sand. The wheels on the original stroller are definitely too
thin to glide across the sand, so they must be replaced with the much wider polyurethane tires.
The front tires will be smaller and in castors, like the original stroller, and the rear wheels will be
bigger and fixed to better support the frame.
11
The main reason for recycling Danielle’s old stroller is that it has a collapsible feature
making it easy to store and transport. The same wing nut system, as seen in this project’s
Alternate Design 2, will be used to secure and disassemble the tires from the chair frame. The
new seat will probably not be compatible with the collapsible design, so it will have to be
removable as well. The overall advantage to this design is the conciseness of the disassembled
parts making it easy to transport.
The optimal design is based mainly off of the third alternate design for Danielle’s project.
The design fits best with the required specifications, as it is already collapsible and the frame is
relatively lightweight. The largest wheels will be removable in order to make the chair even
more portable, easy to lift and store. The design is also very cost efficient because we received
the frame for free from the client and it is preassembled, saving time as well.
2.2 Optimal Designs
2.2.1 Objective
2.2.1.1 Annalee The chair that was designed and is being modified for Annalee will give her more
independence in moving around in her backyard. The power chair has an actuator that controls
the tilt of the seat. The tilt can be controlled manually, and an automated control feature is being
implemented. An accelerometer on the seat will register the angle at which it is sitting. The
accelerometer’s output is read by a microcontroller which in turn controls the actuator to
automatically level the seat so that Annalee is better able to control and maneuver her chair on
the uneven terrain.
Figure 6: Large beach wheelchair wheel. Figure 7: Small beach wheelchair wheel and caster assembly.
12
2.2.1.2 Nathan An all-terrain wheelchair was built for Nathan last year by one of the senior design team.
The chair malfunctioned and the four-wheel-drive caused the turning of the chair to be bumpy
and unsafe. The front powered wheels are being replaced by caster style wheels so that the chair
can turn and maneuver much more safely and easily. The joystick is being replaced with a more
robust one that can withstand more aggressive use from Nathan, and the electrical controls will
be wired correctly as to avoid any further malfunctions.
2.2.1.3 Danielle Danielle’s family would like for a wheelchair to be designed that would enable her to
move across a sandy beach and into the water, while being lightweight and easy to transport and
store. Thus, the basic frame of this wheelchair will be an old cruiser stroller that Danielle used to
use when she was younger. The size of the frame is adequate for her size now and the overall
design of the beach wheelchair. It has a built in feature of the frame back and handlebar
collapsing and folding in on the chair bottom, creating an easily stored and transportable
wheelchair. Additions will need to be made to the chair in order to make it beach-worthy. Instead
of conventional wheelchair tires that are relatively thin and would sink into the sand as they
moved across the beach, the tires on the beach wheelchair will be “balloon” tires made of
polyurethane. Two of these tires will be larger and fixed on the front of the wheelchair, while
two slightly smaller tires will be mounted in casters on the back and will be able to freely and
independently rotate. A new chair will need to be created and mounted in order to fit Danielle
now and as she grows into the chair.
2.2.2 Subunits
2.2.2.1 Annalee
Mechanical
Actuator The actuator is positioned under the seat of the power chair and controls the tilt of seat
with respect to the base of the chair. An electrical signal from the actuator control unit results in
movement of the piston in the actuator. The actuator control unit, in turn, receives input from
either the manual tilt control buttons, or from the automated tilt sensor, depending on which
mode is selected by the occupant. When the piston moves, it creates a torque at the hinge that is
located at the rear of the seat. Based on the direction of the piston’s movement, it will tilt the seat
backwards or forwards. The tilt of the seat is used on hills to prevent Annalee from falling
forwards out of the chair when she is travelling downhill, and to give her better visibility and
control when she is going uphill by keeping her level.
Electrical
Batteries Two 12 V, 75 Ah, Deep Cycle batteries provide all the power necessary for the power
chair to operate. The batteries are wired together in parallel, providing a total of 24 V of power to
the components on the chair. 75 Ah is the equivalent of the batteries being able to supply a
steady current of 75 Amps for one hour. None of the components on the power chair draw that
13
much current, but the higher Amp-hour capability of the batteries will ensure extended use
periods for the chair. Deep Cycle batteries are built to be discharged anywhere from 50 to 80%
before they have to be charged again. This allows for long usage periods necessary to operate a
power chair, before the batteries need charging [4].
Charger A 3-stage charger is used to charge the two main 12 V batteries. A 3-stage charger is used
because it helps lengthen the life of the batteries by preventing them from being overcharged if
left charging for too long. The charging unit charges the batteries quickly with a high current rate
until the battery voltages rise to about 80 to 90%. At this point, the current is reduced, and the
charger outputs the maximum voltage of the batteries. This ensures that the batteries will charge
fully without being damaged by excessive amounts of current. Finally, the charger reaches stage
three of the charging, commonly called “trickle charging,” which is used to prevent the fully
charged battery from discharging [4].
Accelerometer The accelerometer will act as a tilt sensor to allow the seat to automatically level itself.
The accelerometer being used is an ADXL335 from Analog Devices. It is a tri-axis
accelerometer that can measure the static acceleration of gravity for use in tilt sensing
applications such as this. The accelerometer runs off of a single supply voltage between 1.8 and
3.6 V, and outputs a conditioned voltage for each of the three sensing directions [5]. The output
of the appropriate direction will be wired to the input of the microcontroller that will be
described later, which will then control the actuator’s movement to level the seat when it travels
up or down a slope.
Figure 8: ADXL335 accelerometer that will be used as a tilt sensor on Annalee’s power chair.
Software
Microcontroller A PIC16F874 microcontroller will be the heart of the automatic leveling seat. The
microcontroller is programmed using C. The output voltages from the accelerometer will be read
by the microcontroller. Based on these values, the microcontroller will send a signal to the
14
actuator control unit causing the actuator to extend or retract, changing the tilt of the seat so that
it is level. The operator will be able to decide between automatic and manual control of the seat’s
tilt. When manual control is used the microcontroller will still operate, it just won’t be able to
send signals to the actuator control unit. This way, once automatic control is selected, the seat
will begin to adjust right away.
2.2.2.2 Nathan
Mechanical
Suspension and Wheels The four-wheel-drive system that was implemented on the chair caused problems with
the turning ability of the chair. Because all four drive wheels are fixed, the turning causes the
tired to be dragged sideways, resulting in a bumpy and unsafe turn. In order to remedy this, the
front suspension and drive wheels will be replaced with free spinning caster style wheels. This
will result in the chair being only two-wheel-drive, however, it will be much safer to use and
maneuver. When the rear wheels spin in opposite directions or at different speeds to turn the
chair, the front wheels will be able to spin and rotate freely without any resistance, allowing the
chair to turn without jumping and possibly tearing up the lawn or other surface it is riding on.
Overall the chair will be much easier for Nathan to control on any terrain.
Figure 9: New caster assembly that will be built for use on Nathan’s power chair.
Battery and Electronics Housing The battery and electronics housing that was built on the chair was made out of Plexiglas.
Due to the size and weight of the battery, the housing did not hold up and has broken and fallen
apart. A new housing will be purchased and modified to fit on the chair. This new housing will
better support the weight of the battery and will help keep the other electrical components secure
and protected from the elements, while allowing easy access to all of it in case the need to
replace anything arises.
15
Electrical
Joystick The joystick that was originally implemented on the chair is rather small and flimsy.
Nathan’s parents said that Nathan tends to be a little rough with the things he handles because he
does not realize that he is causing harm to them. Therefore, the joystick is being replaced with a
more robust one that will better withstand the aggressive treatment that Nathan will give it. The
new joystick has a metal housing and a stronger joystick shaft that will last longer. The joystick
is connected to the chair through a 15-pin D-Sub connector which will allow the joystick to
easily be removed if it has to be repaired or replaced in the future.
Figure 10: Image of the new joystick to be used on Nathan’s power chair.
Battery A 12 V, 200 Ah, Deep Cycle battery is used to power the chair’s two motors. The Deep
Cycle battery and 200 Ah output will allow the power chair to be used for an extended period of
time before it has to be recharged. This will prevent the chair from dying after a very short trip to
the beach or other family outing. Nathan will be able to use his power chair for the entire length
of an outing and then be able to charge it when his family is at home again.
Motor Controller A Sabertooth 2x25 motor controller is used to translate the joystick movement into the
appropriate directional rotation of the two powered wheels. The motor controller takes power
from the battery and feeds it to the correct motors when the joystick is moved. From the battery
power, the Sabertooth 2x25 can output 5 V to power the joystick, and can read the two
directional output of the joystick based on the voltage values that are returned to inputs S1 and S2
on the motor controller. Based on these values, the controller sends voltage signals to motors 1
and 2 so that the chair moves appropriately.
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Figure 11: Sabertooth 2x25 motor controller used to control the movement of Nathan’s power chair based on the input of the
joystick.
Kill Switch The kill switch will be the overall power switch for the chair. When the switch is in the
closed position, power will be allowed to travel from the battery to the motor controller so that
the joystick will function and the controller will be able to power the motors. When the switch is
in the open position, all power to all of the components of the chair will be cut. The switch will
be placed at the rear of the chair on the outside of the electronics housing so that it can be easily
accessible to anyone that needs to shut the chair off in an emergency. The switch will also help
in storing the chair because the Sabertooth will be disconnected from the battery, increasing the
length of time that the battery will last before needing to be recharged again.
2.2.2.3 Danielle
Mechanical
Wheelchair Frame
The overall frame of this wheelchair will be a recycled stroller that Danielle had used
when she was younger. This particular stroller frame has a wider, more square base than most
other conventional strollers out on the market, which makes it ideal for supporting the larger
tires. The frame consists of hollow tubes made of steel for strength and durability. In the middle
of the long bar that makes up the back of the chair, there are two releases that hook the chair into
place or make it fold down and collapse onto itself. This is ideal for storage and transporting in a
confined trunk or van space.
Since different tires will be used with much larger dimensions, the frame by itself cannot
support all four tires while staying level with the ground. Additional bars that extend down will
have to be added to the front of the chair frame in order for the wheel axle to enter and be level
with the back tires in casters that are of a slightly different diameter.
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Figure 12: Image of the original stroller and the Solidworks representation of the modified wheels on the frame.
Tires/Casters The tires for this wheelchair are custom made “balloon” tires that are quite large. They
are made of polyurethane and filled with air to make them durable yet lightweight. These special
tires are made to be very wide across which makes a very large contact area with the ground.
This enables a much greater weight distribution across the tires as they touch the ground. Like
with snowshoes, the reasoning for this is making a base with greatly increased surface area
makes it so that there is less weight pushing down against the ground at any given point. This
allows the wheelchair to practically glide across the sand as it moves. Typical tires and
wheelchair wheels would sink into the sand as they move due to the decreased weight
distribution that the thin wheels provide.
Figure 13: Larger polyurethane “balloon” wheel and smaller polyurethane “balloon” wheel in the caster housing.
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The four tires are going to be of two different sizes for the sake of being put in casters
and turning. The front two tires will be fixed and attached to the frame extension as to
accommodate for the larger size of the wheels. These tires need to be relatively large in order to
provide maximum weight distribution so it doesn’t sink in the sand. These two tires will be made
to come off the frame in order for easier storage and transport, secured to the frame via a wing
nut and bolt or a pin. The other two tires will be in casters, which are devices that contain an axle
and house the tire from both sides. These casters are attached to the frame of the chair and are
able to rotate freely and independently so the chair can turn. These two tires must be smaller to
accommodate the casters and be able to fit under the chair. Typically, wheelchairs are seen with
the casters on the front so they turn like a car or shopping cart. The casters instead are placed in
the back. The uneven and changing terrain of a sandy beach makes it inherently hard to turn a
wheelchair. The casters are placed nearest to the handlebar so that a lesser amount of torque is
needed to turn the chair, making it easy to overcome the difficulties of moving across such
uneven terrain.
Seat
The old seat in the stroller is too small for Danielle to fit into comfortably. It must be
taken out and replaced with one that she will fit into. It must also be considered that the seat may
get wet from the seawater. The seat cushion will be a conventional wheelchair seat, but it will
have to also be wrapped in a waterproof sleeve to prevent it from being ruined by the saltwater.
The seat back will be made out of a mesh fabric that is porous and easy to dry if wet. The seat
bottom will be supported by a base addition made to the wheelchair frame, while the backing
will be incorporated into the existing back poles.
3 Realistic Constraints
3.1 Annalee
Health and Safety
The power chair that is being modified for Annalee is meant to keep her level in the chair
as she traverses the terrain in her yard. Annalee has tipped one of her chairs over in her yard so
the main concern is to avoid this happening again. The restraints that are built into the seat will
hold Annalee in the seat, and the automatic leveling system for the seat should keep the chair
balanced so that it does not tip over when Annalee is using it.
Sustainability
The power chair should last a number of years so that Annalee can enjoy it for that
extended period of time. The chair itself is durable and if treated properly and maintained, should
last a number of years. The batteries are the only thing that should have to be replaced, and the
time at which they need to be replaced will depend on how often the chair is used and how many
charge/discharge cycles the batteries are subjected to. Seeing as Annalee is still a young girl, she
will likely grow in the coming years as well. In order to plan for this, the seat is easily removable
and can be replaced with a larger one.
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Environmental
The power chair is built to be used in a number of environments. In order to be usable in
these environments, the chair must be able to withstand a large range of temperatures and other
environmental conditions for an extended period of time. Along with environmental effects on
the chair, there are ways that the chair can impact the environment. The two-wheel-drive and
casters will prevent the wheels from tearing up lawns when turning. The batteries, if not disposed
of properly when replaced, could impact the environment greatly as well. The client will have to
understand the impacts of improperly discarded batteries and how to properly dispose of the ones
on the chair.
Economic
All-terrain power chairs that are commercially available today can cost $10,000 or more,
making purchasing one difficult for many people. Designing and building one for a client is more
feasible when the parts and components of the chair can be purchased for relatively low prices.
In a situation like this, labor charges do not inflate the price of the end product. In this case, the
base chair was purchased for a very reasonable price when it was originally designed, and the
modifications to it are very low-cost. The largest cost will be replacing the batteries.
Social
Annalee loves to explore and move about independently. She is currently unable to do
these things because she is constrained by the limitations of her current chair. When this power
chair is completed, Annalee will be able to move around more independently and participate
socially in more locations and situations such as a local park or with friends in her own backyard.
Manufacturability
This power chair is being custom designed and built for a particular client. The chair,
however, is one that could be used by any number of different people. The major custom feature
would be the size, shape, and fit of the seat. With that said, the overall design of the chair could
be replicated and implemented for any number of different clients. Designs and procedures will
be documented so that the modifications can be replicated by anyone.
Engineering Standards
The modifications to the power chair will not change the standard functions of the chair.
The chair will be operated very similarly to any other power chair that is on the market. This will
allow for the client to have an easy transition from her current chair to using this new chair.
3.2 Nathan
Health and Safety
The power chair being modified for Nathan is meant to be used in many different terrain
environments. In order for operation of the chair in these situations to be safe, the chair must be
stable and strong. The wheelbase on the chair was made wide enough to allow for greater
stability on uneven terrain, and the frame is built to withstand any bumpy terrain that it may
encounter. The seat of the chair also has a harness that will keep Nathan strapped securely into
the chair whenever he is operating it.
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Sustainability
The power chair should last a number of years so that Nathan can continue to enjoy using
it as he grows older. In order to accommodate for Nathan’s growth, the seat of the chair was
made adjustable in many locations so that it can be made as comfortable as possible for Nathan
to use at all times. The seat is also removable so that is can be replaced or modified appropriately
as Nathan grows. The battery will have to be maintained, charged on a regular basis, and
replaced when it dies. The life of the battery will depend on how often the chair is used and how
many charge/discharge cycles the battery is subjected to.
Environmental
The power chair being modified for Nathan must be able to operate in a number of
environmental conditions. The chair must withstand a large range of temperatures and terrain
types. The large wheels and wide wheel base make the chair stable and useable in most terrain
situations. The removal of the four-wheel-drive and addition of caster style wheels in the front
will allow the chair to maneuver on all types of terrain without destroying lawns and other
surfaces. The battery on the chair could also pose a threat to the environment if it is not
maintained and disposed of properly. The client will need to be informed of the proper ways in
which to dispose of and replace dead batteries for the chair.
Economic
See Economic Constraints in Section 3.1.
Social
Nathan enjoys spending time with his family and friends during outdoors events, but is
currently unable to do so independently due to the constraints of his current power chair. The
power chair that is being designed will allow Nathan to enjoy the events with his family and
friends while being able to move about independently.
Manufacturability
See Manufacturing Constraints in Section 3.1.
Engineering Standards
See Engineering Standards in Section 3.1.
3.3 Danielle
Health and Safety
The beach wheelchair needs to be both wide-based and be low to the ground so that
Danielle has a low center of gravity and has minimal risk of falling out or tipping the chair over
as she is using it on the beach. The wheelchair must also be lightweight so that it can be easily
handled and moved. This allows for the one pushing the wheelchair to maintain control and not
have to chase after it. The polyurethane tires should be kept away from an open flame source as
it can ignite.
Sustainability
Since there are no electrical components in the beach wheelchair, this device should have
a relatively long lifetime of at least five to ten years. The frame is very durable and should not be
21
prone to deformation or damage over time, if properly taken care of. The polyurethane tires are
also durable and should last a long time, though most likely not as long as the overall frame as
they are more prone to wear and may have to be replaced if a tire gives out. As Danielle grows,
she may need a larger seat to accommodate her body. Since a conventional wheelchair seat is
going to be used here, she may not need an upgrade.
Environmental
Ideally, Danielle and her family would like to use this chair during a nice hot, sunny day
at the beach. The frame and balloon tires are made to withstand at least an ambient temperature
of 110oF, which is extreme for a day at the beach. The balloon tires can move across sand or
pebble beaches as well as most other typical walking terrain. It is advised to avoid using this
wheelchair in places with jagged rocks or other sharp obstacles.
Economic
Commercially sold beach wheelchairs run into a price range of close to a thousand
dollars. Provided Danielle’s family goes to a beach with a beach wheelchair rental station, it may
be hard to find one that is available due to their popularity. Since they are fond of beach trips, if
they continued to rent every time they went, only for a given amount of time, they would spend
so much more extra money than they needed. By using a recycled frame, while still buying
custom tires, Danielle’s family is much better off and saves a bundle of money in the long run.
Social
Danielle is a very active girl and loves to go on vacations with her family and friends.
With this new beach wheelchair, she will be able to freely go across the beach and even into the
shallow water in order to play and enjoy herself. The wheelchair will ideally have a basket or
pouch where she can keep her beach supplies and toys.
Manufacturability
The overall frame is made of a recycled stroller that Danielle used when she was
younger. The only additions that need to be made to it are replacing the wheels with the custom
balloon tires, adding onto the frame to accommodate the new wheels while making the chair
level, and making a new seat for the chair. Additions to the chair can be made easily via welding.
The ordered tires can be placed in the chair easily enough, either by directly connecting and
securing with removable nuts or by fitting into casters that will be welded on. The seat will be
taken off of a conventional wheelchair and then welded onto the stroller frame.
Engineering Standards
The modifications made to the stroller to make it a working beach wheelchair will not
compromise the function of the stroller. It will be intact and still hold its occupant in the same
way it did. The new chair will be operated in the same way, only the caster tires will be in back
making it easier to turn on the sand due to less required torque.
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4 Safety Issues
4.1 Annalee The design of the chair should allow for safety both during operation and when the chair
is not being used. The mechanical components of the chair must not be harmful, and must make
the chair itself safe and secure. The wheels and the width of the wheelbase must be large enough
to keep the chair stable in the different environments that it will be operated in. Other moving
parts such as the motors and actuator should not be assessable by the operator while the chair is
in use so that Annalee cannot hurt herself while she is in the chair. The suspension and automatic
leveling of the chair should also help to keep the chair more stable as it traverses the different
terrain types.
Electrical components, especially wires carrying power from the batteries must be out of
reach and concealed so that they do not cause harm to the operator or others around the chair. All
of the electrical components could be shock hazards so they must be made as safe as possible.
All wires must be checked for possible shorts and no wires should be exposed to the elements or
other components of the chair.
4.2 Nathan The power chair design should account for safety both when the chair is in use and not in
use. The mechanical components, namely moving parts such as the motors and wheels, should
not be a danger for the operator or those around the chair. While he is sitting in the chair, Nathan
will be unable to easily reach or access any of the moving parts, providing added safety and
security for him. The wheelbase of the chair must be kept large enough as to prevent the chair
from tipping over on uneven terrain. This will ensure a safe and stable ride when Nathan is
traversing hills and trails in the woods.
The electrical components, especial wires carrying high amounts of current from the
battery to the motors must be kept out of reach of Nathan and others while the chair is in use. All
electrical wires and other shock hazards must be made as safe as possible. Most of the wiring
will be concealed within the frame of the chair as to avoid possible harm to Nathan or anyone
around the chair, and to protect the electronics from the elements. All wiring will also be check
for possible shorts or other problems that could affect the chair when it is being used.
4.3 Danielle The design of this chair allows for safe operation and simple storage. The frame of the
wheelchair is lightweight and sturdy so that it is easily moved and doesn’t cause a problem in
transport. It will not bend or break while it is in use so it won’t harm Danielle. The tires are filled
with air and are relatively lightweight. If Danielle’s chair were to accidentally bump into
someone else on the beach, it would not cause significant damage or impact to that person. The wheels will be turning on freely turning axles and should not lock up while in use. The
polyurethane in the tires has been fully reacted and now inert, so is should be quite resistant to
chemical reaction and degradation. The only concern is that polyurethane can ignite if exposed to
an open flame. Since this will not likely occur while on the beach unless there’s a bonfire, this
should not pose a threat to Danielle as she uses her chair. There isn’t anything in the wheelchair
that Danielle would be allergic to.
The client has requested that the wheelchair be able to go into the water for Danielle to
play. The main concerns here are the chair being able to float and the chair being prone to get
swept away by the water. Since the frame is a lightweight design and the tires are filled with air,
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the chair should stay relatively buoyant. The problems here are the extent that the steel frame
will weight down the chair in the water and how prone the chair will be to tip over in the water,
causing a safety concern for Danielle. Floatation devices will most likely needed to be mounted,
like the small orange floating boards that beach lifeguards use, on both sides of the chair to
ensure stability. The chair must also not be prone to being carried off by the waves. Making the
chair too light would cause this problem. Ideally, the wheelchair should overall be confined to
the sand and shallow water so that Danielle can play safely. Also, someone should be with her at
all times in order to operate the wheelchair.
It is also important to point out that the person who is operating the movement of the
beach wheelchair will need to walk very close to the tires in the casters. As the person walks
along the beach and turns, they should be aware of how the tires are turning so that they don’t
walk into or get run over by the tires.
5 Impact of Engineering Solutions Power wheelchairs cost thousands of dollars on average and all-terrain power chairs can
cost ten thousand dollars or more. Using a pre-made base frame, or fabricating a frame from
scratch, and building one’s own all-terrain power chair can be more cost efficient than
purchasing one from a distributor. Assembling a chair from off the shelf components decreases
the overall cost of the end product and when someone builds their own, they do not have to pay
for the labor which greatly increases the price of commercial products. As long as the self-made
chair has the same functionality as the commercial product, it is a viable economic option. The
chair may not be as flashy and sleek as a commercial product, but it will work like one
nonetheless.
By constructing a beach wheelchair out of recycled parts and with only a few
modifications, people can build themselves a fully functional beach wheelchair at a fraction of
the cost it would be to buy one off the market. In this dwindling economy, most consumers are
willing to cut corners as long as the product functions properly and is cheap to buy or make. By
using parts from other wheelchairs and strollers, the amount of overall waste material is
minimized as well as impact on the environment. If more of these easily made beach wheelchairs
are made and sold for a lower price, more and more consumers will be able to buy these
wheelchairs for those in need or just for fun. This will enable more people to have opportunities
to go to the beach when they would otherwise be confined to just a regular wheelchair without
access to the sand.
With all three of the projects, the clients are more able to socialize in environments that
were much more difficult for them to access. The products that are being created and modified
for them allow for more independent movement in these environments allowing them to enjoy
more time with friends and family.
6 Life Long Learning One of the most important techniques we’ve learned is that of the engineering design
process. We’ve brainstormed a number of ways to solve a certain problem, and found the best
qualities from each idea to put together a finalized design. We are gaining experience as
contractors, being given a problem and using our unique talents to come up with a creative
solution, that can be used when we enter the workforce as engineers. We have also worked with
clients for their projects and used their input and feedback to satisfy their requirements, which
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leads to a successful design. In designing the product, we have researched cheap, easy-to-use
products that are already on the market and can be incorporated into our design. In doing this, we
greatly reduce the overall cost and time needed to produce the end product without
compromising function.
During the design process, we have learned to use and design prototypes with the 3-D
CAD software package, Solidworks. The capabilities of the software allow for detailed and
intricate design work. We have a better understanding and appreciation for the number of
individual parts that go into a single design. Through Solidworks, we can also create simulations
that test the products structural integrity before it is produced. This capability reduces the amount
of time and material that could be wasted in creating a product that could fail when subjected to
the required loads. Overall, Solidworks is an invaluable tool in our arsenal as engineers.
Following the design and testing of a product in Solidworks, a prototype must be created
to test and analyze the integrity of the design. In order to accomplish this, certain parts of the
design will likely have to be fabricated from scratch. Through taking our machine shop safety
course, we have learned how to properly use a number of pieces of equipment to turn the
Solidworks model into a physical part. From milling parts out of solid metal blocks to carving
out contours on cylindrical parts with the metal lathe, the knowledge of how to use the
equipment is invaluable in future design products. Other specialized skills such as welding will
also be learned as necessary to complete our projects.
Building on our previous knowledge of programming, we will be better applying our
skills to make our product work properly. We will be using a microcontroller to convert physical
inputs to electrical signals for which the chair will operate properly. A lot of trial and error goes
into programming and sometimes the best way to learn is by making mistakes. Ultimately, the
programming of the power chair will expand our thought process with more outside-the-box
solutions to problems.
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7 Budget and Timeline
7.1 Budget
Price Quantity Additional Cost(s) Total
Project 1 - Annalee
PCB $30.00 1 $30.00
Deep Cycle Batteries $150.00 2 $300.00
Total
Project 2 - Nathan
Battery enclosure $20.00 1 $20.00
Electronics enclosure $45.00 1 $45.00
Miscellaneous hardware supplies $25.00 1 $25.00
3/8" stainless stock for casters (1'x1') $73.48 2 $146.96
Total
Project 23.1 - Danielle
Balloon Wheels and Parts $480.00 1 $65.18 $545.18
Aluminum Stock $35.41 1 $35.41
Miscellaneous hardware supplies $40.00 1 $40.00
Total
All projects
Gas usage to date $30.00 $30.00
Foreseable gas usage $75.00 $75.00
Total
Allotted Budget $1,300.00
Amount Spent $845.18
Remaining Budget $454.82
Expected Costs $447.37 Table 1: Budget update, items purchased and amount spent to date bolded.
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7.2 Timeline
Task Name Duration Start Finish Predecessors Resource Names
Modify armrests to move with the seat back
3 days? Wed 1/18/12 Fri 1/20/12 8 Steve
Fabricate new joystick mount
2 days? Mon 1/23/12 Tue 1/24/12 9 Stephen
Modify new battery/electronics case
3 days? Mon 1/23/12 Wed 1/25/12 11,20 Steve
Mount new battery/electronics case
2 days? Thu 1/26/12 Fri 1/27/12 12 Steve
Waterproof the motors and electronics case
2 days? Mon 1/30/12 Tue 1/31/12 13 Steve
Fabricate new front caster parts
1 day Wed 2/1/12 Wed 2/1/12 16 Steve
Assemble new front casters
1 day Thu 2/2/12 Thu 2/2/12 17 Steve
Fabricate front caster mounts
1 day Fri 2/3/12 Fri 2/3/12 18 Stephen
Assemble front caster suspension
1 day Mon 2/6/12 Mon 2/6/12 19 Stephen
Replace electric connectors on motors
1 day Tue 2/7/12 Tue 2/7/12 13 Stephen
Mount seat back onto chair
1 day Wed 2/8/12 Wed 2/8/12 20,13 Steve
Mount and wire joystick to motor controller
1 day Thu 2/9/12 Thu 2/9/12 22 Stephen
Test assembled chair's functionality
1 day Fri 2/10/12 Fri 2/10/12 23 Stephen,Steve
Disassemble chair as necessary and prep for paint
3 days Mon 2/20/12 Wed 2/22/12 24 Stephen,Steve
Paint new parts/repaint chair if color can't be matched
2 days Fri 2/24/12 Mon 2/27/12 25 Stephen
Final chair assembly 2 days Wed 2/29/12 Thu 3/1/12 26 Stephen,Steve
Design new circuit if current one can't be debugged
3 days? Wed 1/18/12 Fri 1/20/12 32 Stephen
Reprogram microcontroller
10 days? Mon 1/23/12 Fri 2/3/12 33 Stephen,Steve
Test chair with microcontroller changes
1 day Mon 2/6/12 Mon 2/6/12 34 Stephen,Steve
Design and order PCB 7 days Mon 2/13/12 Tue 2/21/12 35 Stephen
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Solder components to new PCB
1 day Mon 2/27/12 Mon 2/27/12 36 Stephen
Instal PCB 1 day Tue 2/28/12 Tue 2/28/12 37 Stephen
Clean chair and components/ prep for paint
2 days Wed 2/29/12 Thu 3/1/12 38 Steve
Touch up paint on chair 1 day Fri 3/2/12 Fri 3/2/12 39 Steve
Mount seat back on chair 1 day Mon 3/5/12 Mon 3/5/12 40 Steve
Check for Tumble Forms seat and headrest
1 day Fri 12/16/11 Fri 12/16/11
Stephen,Steve
Fabricate frame extensions for front wheels
2 days Mon 1/23/12 Tue 1/24/12 47 Steve
Mount frame extensions for front wheels
2 days Mon 2/27/12 Tue 2/28/12 48 Steve
Mount wheel axles to frame extensions
2 days Wed 2/29/12 Thu 3/1/12 49 Steve
Assemble rear casters 1 day Fri 3/2/12 Fri 3/2/12 46 Steve
Mount rear casters 2 days Mon 3/5/12 Tue 3/6/12 51 Stephen
Test bouancy of balloon wheels
1 day Wed 1/18/12 Wed 1/18/12
Stephen,Steve
Mount balloon wheels 1 day Wed 3/7/12 Wed 3/7/12 53,52,50 Steve
Fabricate new braking mechanism
2 days Thu 3/8/12 Fri 3/9/12 54 Stephen
Modify seat mounts to accommodate new seat
1 day Mon 3/12/12 Mon 3/12/12 45 Steve
Mount new seat 1 day Tue 3/13/12 Tue 3/13/12 56 Steve
Add lap belt to seat 1 day Wed 3/14/12 Wed 3/14/12 57 Steve
Adjust/modify foot rest 1 day Thu 3/15/12 Thu 3/15/12 57 Steve
Fabricate accessory pouch for chair
1 day Fri 3/16/12 Fri 3/16/12 57 Steve
Mount accessory pouch 1 day Mon 3/19/12 Mon 3/19/12 60 Steve
Fabricate umbrella holder 1 day Tue 3/20/12 Tue 3/20/12 57 Stephen
Mount umbrella holder 1 day Wed 3/21/12 Wed 3/21/12 62 Stephen
Fabricate cup holder 1 day Thu 3/22/12 Thu 3/22/12 57 Stephen
Mount cup holder 1 day Fri 3/23/12 Fri 3/23/12 64 Stephen
Prep frame for paint 2 days Mon 3/26/12 Tue 3/27/12 57,61,63,65 Stephen,Steve
Have frame painted 7 days? Mon 4/2/12 Tue 4/10/12 66 Central CT Coatings
Final assembly after paint 2 days Wed 4/11/12 Thu 4/12/12 67 Stephen,Steve Table 2: Projected timeline for the Spring semester.
28
8 Team Members Contributions to the Projects
8.1 Stephen Elovetsky Throughout the semester, I have put a lot of time into Annalee’s project. At the very
beginning, I removed the auto leveling circuit from the chair and began testing it by moving the
accelerometers to see how the microcontroller and circuit responded to different inputs. Once we
received the new deep cycle batteries, I installed them in the chair and tested the chair’s
maneuverability. I also tested the auto leveling circuit on the chair to see if it responded any
differently. After that, disassembled the breadboard and rebuilt the circuit on a protoboard in
order to make testing and modifications easier. I spent the remaining weeks of the semester
trying to get the circuitry to work properly, however I determined that the microcontroller would
have to be reprogrammed in order for the seat to work properly.
For Nathan’s project, I began by mapping the internal wiring of the new joystick, and
then determined which pins on the d-sub connector each wire corresponded too. Once the
connections were mapped, I soldered wires to the appropriate pins of a female d-sub connector
so that the joystick could be connected to the motor controller and tested. I tested the joystick,
rewired the motor controller and motor connections appropriately, and changed jumper settings
on the motor controller to slow the chair down to a safer speed. Once Steve tested the turning
capabilities, and the stopping ability of the chair on hills, I disassembled the front suspension of
the chair so that we could later build and attach the casters for safer and more efficient turning. I
also disassembled a set of casters that we found in the supply closet in the lab so that we could
use the main components of it to make the new casters to fit the large wheels from the chair.
Along with the front suspension work, I also removed the old battery and electronics box from
the frame to make room for the new one that we will be adding to the chair in the Spring.
8.2 Steven Rogers For Nathan’s power chair, I removed the old armrests from the frame which were
unnecessary for our improved design. I have started to design a new battery and accessory case
for the chair made out of sheet metal and not Plexiglas. I tested the original breaking system
outside on increasingly sloped surfaces, trying to determine if the chair could hold position on a
hill. It was not very successful because it could only stay on slight slopes. Methods of breaking
will be investigated for next semester. Further testing is not possible due to two of the wheels
being switched out for freely moving casters.
For Danielle’s beach wheelchair, I have removed all unnecessary materials from the old
stroller, such as the old seat, arm & headrests, and various straps. The old frame was covered by
foam and duct tape at certain parts along the bottom, which had to be removed for the final
product. I also spent a great deal of time using the program Solidworks to model our stroller and
create a prototype design for he beach wheelchair that included the modified tires. I e-mailed a
representative at Central Connecticut Coatings in order to begin investigating the application of
corrosion resistant paint, which can be done at their shop. I ordered several items for Danielle’s
new chair, such as the balloon tires, custom casters, and an air pump. I have begun looking into
ordering waterproof seats so that Danielle can use her chair in the water. Many are provided at
NEAT Marketplace. I managed to remove the old tires on the stroller and its original breaking
system on the back tires which we won’t be using for this project. I have also looked online for
ordering aluminum metal tube stock for extending the stroller frame to accommodate the larger
wheels.
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9 Conclusion When Annalee received her power chair two years ago, it worked as it was supposed to.
Shortly thereafter, it began to malfunction and became unsafe for her to use. The seat was
designed to level itself based on the angle of the slope that the chair was traveling on, but this
mechanism stopped working shortly after Annalee received the chair. We have been working on
reprogramming the microcontroller and rewiring the auto-actuating circuitry in order to make the
chair more reliable. This way, Annalee will be able to explore her backyard and other outdoor
areas freely, independently, and safely without fear of the chair failing.
Nathan’s power chair was completed last year, though testing and debugging never took
place, thus the chair did not work correctly when he received it. In order to better meet the
clients’ specifications we have altered the overall design to make it more practical and safer to
use. The old joystick was replaced with a newer, more robust one, and the operating speed of the
chair was reduced to be safer and more manageable. The joystick mounting location will also be
moved to a more comfortable and practical location. The old battery and electronics case was too
small and not strong enough to hold the weight of the battery and other electronics. The Plexiglas
was broken when we received the chair, indicating that it was not strong enough to use as the
material for the case. We plan on ordering a new metal case that will be large enough and strong
enough to hold all of the components. The original four fixed wheels didn’t allow the chair to
turn properly or safely, so we decided to redesign the front suspension and replace the fixed
wheels with free spinning casters. With these improvements, the chair will be safe and reliable
for Nathan to use to explore the outdoors with his family and friends.
The beach wheelchair that we are designing and building for Danielle is based off of one
of her old collapsible strollers. In order to make the wheelchair capable of traversing the terrain
at the beach, the wheels are being replaced with wider polyurethane balloon tires that will allow
the chair to be easily pushed across the uneven, shifting sand. In order to accommodate for the
larger frame, we are extending the frame of the chair with additional aluminum stock. The
casters are also being moved to the rear of the chair so that it is much easier for the operator to
turn on the uneven terrain. The seat is being modified to accommodate for Danielle’s growth,
and will be made water resistant so that it will last longer. Corrosion resistant paint is also being
applied to the frame so that it will resist the galvanic corrosion of the sea water. With her new
personalized beach wheelchair, Danielle and her family will be able to enjoy more time at the
beach without worrying about mobility issues.
10 References
[1] Cerebral Palsy. A.D.A.M. Medical Encyclopedia. [Online] [Cited: October 8, 2011.]
