All-Terrain Power Chair

Transcription

1 Final Report - BME 4910 All-Terrain Power Chair Team 10 Prince Alam Marcus Chapman Mathew Kozachek Project for Nathan Lamb Client Contact: Janice M. Lamb 142 Barnes Road Stonington, CT (Home) / (Mobile) / (Office/Fax) Janice.Lamb@linde.com 0

2 Table of Contents: 1. Introduction 1.1. Background 1.2. Purpose of the Project 1.3. Previous Work Done by Others Products Patent Search Results 1.4. Map for the rest of the report 2. Project Design 2.1. Optimal Design Objective Subunits 2.2. Prototypes 3. Realistic Constraints 4. Safety Issues 5. Impact of Engineering Solutions 6. Life-Long Learning 7. Budget and Timeline 7.1. Budget 7.2. Timeline 8. Team Members Contributions to the Project 8.1. Team Member 1: Prince Alam 8.2. Team Member 2: Marcus Chapman 8.3. Team Member 3: Mathew Kozachek 9. Conclusion 10. References 11. Acknowledgements 12. Appendix Updated Specifications Purchase Requisitions and Price Quotes Others (Part Specifications, datasheets, communication protocol commands, etc) 1

3 Abstract: This project involves designing and fabricating an all-terrain power chair that can traverse settings such as walking trails and beaches, located around the client s home and can be operated by Nathan Lamb, despite his medical challenges. Since Nathan is autistic, cognitively and physically challenged, and has myelomeningcoele, commercially available power chairs cannot satisfy the needs of Nathan. Also, commercial power chairs retail between $10,000 to $20,000, so cost is also a major limiting factor. Overall, the purpose of this project is to ensure that Nathan can enjoy recreational activities with his family in an enjoyable and safe manner. To begin the design of the wheelchair, the group found it important to see what other projects and products were fabricated in the past that had similar goals as this project. At the University of Connecticut, a team in the past year modified an all-terrain power chair to better suit the needs of their client. Various commercial all-terrain power chairs also exist, but as alluded to before, prices were very high. Also, patents were researched, both of which were filed in the late 1990s. They both encompass a unique power wheelchair design to travel on rough terrain. Since Nathan is capable of controlling his own movement, the family would like to have the power-chair be operated by Nathan. The team has decided to use a left-hand operated joystick. Also, the family has expressed the desire for an emergency override control, just in case Nathan is in danger. The power chair must also be transportable, so it must satisfy certain dimensions. The power chair must also be intuitive to use for anyone. For example, a person must be able to easily put Nathan into the wheelchair with ease and without damaging the device, which is a problem the family has run into with many assisted moving devices. In addition this design is unique in that it will utilize an actual four-wheeldrive system, which is only found in very high end power chairs. This design will be used because it will be most versatile in many types of terrain. In addition, the power chair will be relatively light weight, since most of the frame will be constructed out of aluminum. Since Nathan is still young, the design must accommodate his growth. Also, it will have a shock absorber at every wheel to absorb any bumps encountered when used. This feature is only found on very high-end power chairs. Another important objective for the power chair is to make sure that is safe for Nathan and anyone surrounding him. The design will be implemented by analyzing the mechanical and hardware components, such as the frame/chassis and suspension. In addition, the possible electrical and software aspects will be discussed. Overall, the cost was above slightlyabove $2,000. The most expensive components include the aluminum stock, bearings, motor controllers, and the four motors. With all of these aspects analyzed, the team hopes to have designed and built an all-terrain power chair that Nathan will be able to use on all sorts of terrain, in a safe and efficient manner. 2

4 1. Introduction 1.1. Background The client, Nathan Lamb, is an 11 year old male. He currently weighs between 40 to 50 pounds. His height is also about 50 inches. To get more accurate values, the family has been asked to have a medical examiner take proper measurements, which have been reported in the project design section. After meeting with Nathan, it was apparent that he is a peaceful and delightful child to be around. This was reiterated when his parents discussed with the group how he gets a lot of friendly attention at school, especially from the females. It was obvious that he enjoys being outdoors with his family, so it is obvious that an all-terrain wheel chair would greatly increase Nathan s mobility and ability to enjoy activities with his family. It was apparent that due to his medical conditions, Nathan tends to fidget a lot when seated. He also has the tendency keep his right arm high in the air, by his head. Consequently, the family requested that seating have a lot of support. Nathan resides in Stonington, CT. His family has built a wonderful, custom home that is fully wheelchair accessible with widened doorways, open floor plan, and an elevator. He lives on a level 16 acre, wooded property. The family intends to establish gravel trails through the property, so Nathan will be able to traverse the landscape with more ease, once the power chair is completed. He also lives a few miles from coastal beaches. He currently attends Mystic Middle School in the Stonington. He is given a lot of caring attention. The school district has even purchased various assisted moving devices, so he can travel and fit in better within the school. Also, his school therapist has been on a mission to find a onearmed drive mobile stander for Nathan to utilize to be able to participate more actively with his peers in a standing position. In addition, he has a special education teacher, named Gabrielle LaChance. As one can see, his family and the school district have taken a great stride to ensure that Nathan can be accommodated with as much comfort as possible, despite his challenges. The client has various medical challenges. He is on the autism spectrum. In other words, he has a disturbance in physiological development in which use of language, reaction to stimuli, interpretation of the world, and the formation of relationship are not fully established and do not follow a typical pattern. In addition to being mentally challenge, he is also physically challenged. He cannot walk, stand, sit up, or move great distances without assistance. Also, he has a weak trunk, so Nathan usually needs a supportive seat. In addition, he also has spina bifida, which is also known as myelomeningcoele. This is birth defect on which the backbone and spinal cord do not properly close before birth. In Nathan s case, this caused partial paralysis of the legs and weakness of the hips, legs, and feet. Due to spina bifida, Nathan has hydrocephalus, where there is a buildup of fluid inside the skull. To remedy this, Nathan had an operation where the fluid buildup is drained to his bladder through a pipe for excretion. His parents also mention that he may have scoliosis due to his abnormal sitting posture. He tends to sit slanted. Despite all of his conditions, his family has expressed that he is capable of operating a power chair on his own. Nathan is adept at using his left hand, so the power chair controls would have to be implanted for left-hand control Purpose of the Project 3

5 The ultimate purpose of this project is to fabricate an all-terrain power chair that is capable of traveling on light trails and the beach and be operated by Nathan, without the family having to worry about his safety or comfort, so the family and his school district can include him in more recreational activities. All of Nathan s current assisted movement devices serve singular purposes. For example, Nathan s Standing Dani can only be used, while standing up, is manually propelled by, and can only be used comfortably on perfectly flat surfaces. Also, many of his devices are not intuitive to use. This property is essential, so anyone that helps Nathan into his device does so properly and without damaging the device. With all that said, the design team will work to make a versatile, safe, and comfortable power chair that can easily be used by Nathan and his family in all sorts of terrain Previous Work Done by Others Products There are several products and past projects that have been designed to achieve goals similar to those of this project. Essentially, the universal goal of the products and projects were to create a power wheel chair that can traverse all sorts of terrain that is intuitive to use and provides uncompromised safety and comfort. In the spring of 2010, a low center-ofgravity all-terrain power chair was designed for a client based in Tolland, CT. The client had cerebral palsy, and similar limited mobility problems as Nathan did. The team bought a used Quickie S626 power chair, and simply altered the basic design to better suit the desires of their client. It utilized a two-wheel drive system, operated by right-handed joystick. The overall implementation of this power chair cost around $4,400. Figure one shows the final product. This past project is similar in Figure one: Power chair from past UConn project 1. that it utilizes oversized tires and joystick controls. It differs in that the current project will be four-wheel drive instead of two-wheel drive. Also, the current implementation will not be based on a commercial product. Figure two: X4-Extreme power chair 4. Not only have University of Connecticut students designed similar projects, but devout mobility assistance companies have also developed all-terrain power chairs. Planet Mobility offers the X4-Extreme four-wheel drive power chair, manufactured by Magic Mobility. This product is designed to be driven on sand, soft ground, wet ground, or slippery surfaces with minimal trouble. It is capable of climbing curves as high as six inches. The wheels are large with a 14 inch 4

6 diameter and a 5 inch width. Like the past project, it is operated by a joystick. The X4-Extreme weighs 289 pounds. It retails for a base price of $16,995, and the price can rise by a couple thousands, depending on equipped options. The product can be seen in figure two. This product is similar to the team s project in that the current implementation will utilize four-wheel drive and be operated by a joystick. This product differs from the team s project in that the implementation will weigh less and be far less costly. Jazzy Power Chairs is a company that has developed a wide variety of powered wheelchairs. The Jazzy 614 is designed for varied terrain. This power chair has six wheels, where the two center oversized wheels are powered and a pair of wheel casters for the front and back of the chair are implemented for enhanced stability. It also has dual suspension for enhanced comfort. Like the other devices, this one is also controlled through a joystick. It weighs 300 pounds and has a price hovering around $10,000. The device can be seen in figure three. Like this device, the team plans to use suspension to ease the ride on the terrain. Unlike the Jazzy 614, the team will have a higher ground clearance than 2.25 inches to improve versatility, utilize a four-wheel drive system, and weigh less. Figure three: The Jazzy Patent Search Results In 1998, Adoolf Hammer filed a patent for a self-powered, all-terrain vehicle to assist paraplegics in transportation 6. This design used an internal combustion engine that was coupled to a hydraulic drive to power the vehicle. The hydraulic force was needed for initiating and controlling directional movement. Therefore, the design uses fuel tank for the hydraulic and combustion engine system. The device was controlled by a left and right pivoting lever. It also had an emergency steering wheel, in case the device became inoperable. Another patent was filed in 1999 by Walter E. Schaffner 7, James P. Mulhern, and Stephen J. Antonishak 8. The patent was about a front wheel drive power wheel chair. In addition, it uses independent suspension for comfort. It is also battery operated, which supplies power to the two independent motors. Also, it utilizes six wheels. The center pair is electrically driven, while the other two pairs of wheels act as supporting casters to stabilize the power chair Map for the rest of the report The rest of the report will discuss many preliminary designs, and then an optimal design that combines all of the best aspects of the preliminary designs. The optimal design will give details about the overall power chair by discussing the various parts of the power chair in terms of subunits. Next, the realistic constraints will be discussed. This will encompass engineering standards, economic, environmental, sustainability, manufacturability, ethical, health and safety, social, and political considerations. In addition, various safety issues will be discussed. Then the impact of engineering 5

7 solutions will be discussed, as well. Also, life-long learning accomplishments that will be achieved from carrying out this project will be discussed. Then, the budget and timeline will be displayed and discussed. After that, contributions of all the team members will be talked about. After this section, there will be a conclusion, references, acknowledgements, and the appendix. 6

8 2. Project Design Design One This design of the all-terrain power chair will incorporate the use of six wheels. Most power chairs that are currently on the market utilize a four-wheel drive design. The more expensive models, like the X4-Extreme power chair, are powered at all four wheels, while other models have four wheels, but are only rear-wheel driven. For example, a past University of Connecticut team redesigned a Quickie S626, which was only rear-wheel driven. The past team project can be seen in the figure one. As one can already begin to tell, most power chair designs use only four wheels. However, there are some designs that do make use of six wheels. The Jazzy 614 uses a six-wheel design, where the center pair of wheels are the largest and powered, while a set of wheels are placed in the back and the front of the power chair to have a total of six wheels. The front and back sets of wheel are simply small casters. A picture can be seen in figure three. Another six-wheel design is similar to the four-wheel designs. However, the design utilizes casters in the rear. They are only utilized when the wheelchair is tipping backwards. These casters act to make sure the power chair does not tip backwards when traversing rough terrain. As one can see, there are a lot of physical designs to explore in regards to power chairs. This design will discuss the use of six wheels. Although, this is a more uncommon design, this design does have benefits that can be utilized for the optimal design. With the use of six wheels, the power chair will inherently be more stable, leading to a much safer design. Also, since only two large wheels and four small caster wheels would be needed, there would be a possibility of reducing the overall weight of the design, since four large wheels would not be needed. Also, six-wheels would allow more articulation on rough terrain, which could lead to a more comfortable ride. In addition, this design can save costs in that only two wheels would need to be powered instead of all four, with the sacrifice of having less overall power. However, this will ensure that less battery power will be needed, which further reduces with overall weight of the design. To begin design, a pre-existing chassis will be searched for that utilizes a six-wheel design. If one is found at a suitable price, then the chassis will be used. Otherwise, the chassis will be fabricated from light-weight aluminum. On each side of the power-chair, three spring and shock absorber units will be used to enhance ride quality on rougher terrain. Two will be placed on the front and back of the chassis to dampen the roughness experienced by the front casters. A spring in the center of the chassis, right above the large, center wheels will provide overall suspension, which will mainly help dampen roughness experienced by the two large wheels. Overall this design for the Figure four: CAD design on one side of the power chair chassis 2. 7

9 wheels will allow optimal ride quality with a light frame. The DC motors will be placed right next to the large wheels for direct power. High density rechargeable lithium ion batteries will be used to power the motors. The quantity of batteries will be dependent on the power requirements of the direct current motors. Both the motors and batteries will be enclosed in an aluminum box to protect the various components from exterior elements. This aluminum box will have the seat right above it. The aluminum box will have a heavy duty hinges and opening mechanism that will allow a used to go to the rear of the power chair, and simply unlatch the mechanism to lift both the seat and the top of the box to have the motors and batteries easily exposed for easy maintenance, as necessary. An ergonomic seat will be purchased for optimal comfort. Armrests and headrest will also be in place for further comfort for the client. Ultimately, the seat will have to function to provide as much support as possible due to Nathan s physical limitations. The group will consult NEAT marketplace in Hartford, CT and other experts on how to get the most suitable seat at a reasonable price. The following table shows Nathan s measurements, as measured by his physical therapist on October 12, The chair will be designed to best accommodate these various measurements and allow provisions for possible expansion since Nathan will possibly grow. Table One: Nathan s measurements as of 11/15/10 Location Chest width 9 Shoulder-shoulder with chest width 13 Back of Hip/femur to popliteal angle 15º Popliteal angle to heel-leg length 10 Full heel to top of head 44 Base of pelvis/bottom to top of head 26 Base of pelvis/bottom to shoulder height 19 Foot length 7.5 Top of shoulder to bottom of elbow 11 Measurement (in inches unless marked) In addition to the electrical components discussed previously, a joystick will be placed on the right armrest, so Nathan can personally operate the power chair. This will operate most aspects of the movement for the power chair. For example, if pushed forward, the power chair will propel forward. If pushed backward, the power chair will apply power to the disc brakes and then proceed to move backwards. The rate at which the brakes are applied will be controlled through an algorithm to prevent a jerking caused by inertia during a quick stop. Overall, the joystick will control both speed and direction of the power chair. 8

10 Since this design does not have any rotating wheels, a microcontroller will be implemented for many aspects of this design. The microcontroller will process all input commands from the joystick and various buttons and perform an operation. The microcontroller will run off of CMOS digital logic and provide pulse-width modulated signals as an output to an H-bridge, which proceed to send power to the motors. In addition, depending on direction selected for the joystick, the microcontroller will be in charge of sending varying power to each wheel. For example, if Nathan wants to move in a rightward direction, then the left wheel will operate at a faster velocity than the right wheel. This design is far superior to four-wheel drive power chairs in that this operation allows for a very small turning radius. This greatly enhances maneuverability in small areas. The design will incorporate an MP3 jack that will allow a music device to output music to the jack and have the music to be played a reasonable volume through the speakers built into the design of the power chair. A noise sensor will monitor surrounding noise and put the volume of the speakers at a reasonable value. Bogen produces a device called ANS501 that does this function. This will be powered by the lithium ion batteries. These batteries will be rechargeable with the use of a charge inverter that should replenish the battery power supply within a couple of hours. Lastly, both an onboard and remote kill switch will be implemented to stop the device in case any emergencies arise. In order to program all of these components, C language will be used to process all of the inputs of the all-terrain power chair. Due to this choice of computing language, a PIC microcontroller will be used because it is inexpensive and easy to debug. All of the electrical components and wiring will be either housed in the aluminum box next to the motors and batteries or in other enclosed locations to protect all the components from the outside elements. This will ensure safety. 9

11 Design Two Design two will contain a headphone jack that has headphones, which will connect to an ipod for music playback. This is will allow the client to be more comfortable, and he already uses headphones. His right ear is sensitive so this will limit any discomfort. Also, this will allow him to enjoy music, without disturbing anyone else around him. The seat will be able to move if the client encounters an incline going up or down, so that he will remain in the upright position, to prevent any back damage. The seat must provide a safe, comfortable, secure fit. If the client were to climb an incline it will feel as though he is on level ground. For extra security, it will contain anti-tip wheels. This will be accomplished with a type of gyroscopic seat. Also, the adjustable seat will allow for the client to be easily placed into the seat with minimum strain on the person helping. The seat will also be made to fold down to make it easier to be placed in the transport vehicle. As an extra safety precaution, the wheel chair will contain small headlights if the client were to ever be in a dark area or as a way to signal for help. Reverse lights will be used to help warn others around when the wheel chair is in reverse. A horn sound may also be added for the client to warn others if they are in the path of the wheel chair. The joystick will be a VR2 joystick and module, which will allow for easy replacement if needed. The joystick will allow to easy programming of lights and other wheel chair functions. Other minor additions to the wheel chair will include an ability to attach umbrella to block the sun at the beach or rain. Cup holders and a detachable trap for eating or reading, while in the chair, will also be added. Figure five: VR2 joystick and control. 10

12 Design Three This design of the all-terrain powerchair will be as lightweight and compact as possible, while also being modular. Unlike most other four-wheeled designs, this powerchair will have an individual motor for each wheel, allowing for four-wheel drive. This design will furthermore be different from other all-terrain wheelchair designs in the ease with which it may be disassembled. To ensure stability of the wheelchair, the four large wheels will be spread lengthwise from the center of the chair using one lever arm per wheel. This provides forward and backward tilt stability without using a six-wheeled base. All four wheels will be full-sized power wheels, and no casters will be utilized. Individual suspension for each wheel will allow the device to safely travel over rough terrain without tipping the entire chair. The wheels will be mounted with Hall Effect sensors to determine their rotational velocity and report it back to the microcontroller. Four DC motors will be mounted directly beneath the seat. Each will use a U-Joint to axel to U- joint configuration to transfer power to a gear. This gear will be mounted on the lever arm. A chain will then transfer power from the gear to the wheel. This will allow us to fine-tune the gear ratio from the motor to the wheel, as well as allow the end user to easily swap out the gears. By making the gear removable, the DC motors can be removed easily as well. The DC motors will be mounted in a lightweight sheet aluminum casing, form-fitted and welded shut to prevent environmental damage. The top of this casing will be the attachment point to the chair and will remain open at the top to allow removal and servicing of the DC motors. Two rechargeable, high charge-density 12V lithium-ion batteries will be mounted to the back of the wheelchair to provide power to these motors. A high-current four-channel H-Bridge will allow the microcontroller to provide CMOS pulse-width modulated signals to power each of the wheels in both the forward and backward direction. This will allow the chair to be turned without requiring casters, and will also allow us to provide four-wheel drive to the chair. Because the chair will not be designed to move above walking speed, power consumption of the batteries should be relatively low. A separate nine volt power supply will provide power for the microcontroller using standard batteries. A charge indicator will tell the family when they must replace the microcontroller's power supply. Furthermore, the motor power supply will have a physical cutoff switch. This will cut power to the motors as well as send a CMOS-high voltage input to an IO pin of the microcontroller, indicating that the cutoff has been activated and ceasing all motor control output. The frame will be made from 2 by 2 square tube 6061-T6 stock. The hollow nature greatly reduces the weight of the chair, as well as the price of the frame, while retaining a great deal of strength. By custom-fabricating a simple frame we can precisely ensure size requirements of the family as well as size requirements of our components. A simple frame will be used - a square 24 inch by 16 inch square base under which the motors may be mounted, and to which the lever-arms of the wheels will be attached. The edges of this will also provide attachment points for the shock absorbers of the wheels. The back of this square will provide the mounting point for the 'spine' of the chair, to which push handles will be attached, as well as the seat itself. 11

13 For the audio jack, a Dayton RS100T-8 4-inch woofer will be used in conjunction with an STA540 audio amplifier kit. The Dayton RS100T-8 woofer is capable of producing audio frequencies from 20Hz to 20kHz. This is a sufficiently large range for an mp3 player. Furthermore the wattage for the Dayton RS100T-8 is low enough that the woofer can easily be limited in volume so as to not damage the client's hearing. The chair will be controlled by a joystick mounted on the left arm of the seat, as the client is unable to utilize his right hand. The joystick will be a two-axis potentiometer model, and its output will be converted to digital signals by the microcontroller. The powerchair will use a PIC microcontroller as its main computational device. The microcontroller will be programmed in embedded C. Embedded C is easier to use and test than assembly, and allows for more complex mathematical functions without the need for extra packages and strenuous programming. The microcontroller will receive input from both the joystick for control, and the Hall Effect sensors on the wheels. The Hall Effect sensors of the wheels will be used to measure relative rotational velocity of each of the wheels. If the relative rotational velocity of one wheel exceeds that of the others intended to be rotating in the same direction, that is indicative of the tire losing traction. The microcontroller will then transmit less power to that slipping wheel, and more to the others. The seat for the chair will be an ergonomic, comfortable design with a harness designed to keep the client in the chair. High arms of the chair will help to support his trunk and prevent his slouching. The headrest of the chair represents a potential mounting point for the Dayton RS100T-8. Because of our client's tendency to press his right hand to his ear, mounting the speaker in a position where he can rest his ear, while keeping the volume very low, represents a potential way to free his right hand and make the chair more comfortable for him. The seat will be mounted on an extendable boom so our client may be at eye-level when on the chair, yet the chair can also be collapsed to take up less space and fit in our client's family's minivan. To one of the rear wheels will be mounted a mechanical disc brake. This will be operated via a lever on one of the push-arms of the powerchair. This will provide added safety when the electronic failsafe is triggered, as well as provide a brake for the chair when the motors are removed and the family wishes to use it as a rugged push-chair. 12

14 2.1. Optimal Design Objective The purpose of this project is to design and fabricate an all-terrain power chair that can traverse settings, such as walking trails and beaches, located around the client s home and can be operated by Nathan Lamb, despite his medical challenges. Since Nathan is autistic, cognitively and physically challenged, and has myelomeningcoele, commercially available power chairs cannot satisfy the needs of Nathan. Also, commercial power chairs retail between $10,000 to $20,000, so high cost is also a major limiting factor. Also, all of Nathan s current assisted movement devices serve singular purposes. For example, Nathan s Standing Dani can only be used, while standing up, is manually propelled by, and can only be used comfortably on perfectly flat surfaces. It is shown in figure six. Overall, the purpose of this project is to ensure that Nathan can enjoy recreational activities with his family in an enjoyable and safe manner. Figure six: Manual (Left) and powered (Right) Standing Dani [1] The client has various medical challenges. He is on the autism spectrum. In other words, he has a disturbance in physiological development in which use of language, reaction to stimuli, interpretation of the world, and the formation of relationship are not fully established and do not follow a typical pattern. In addition to being mentally challenge, he is also physically challenged. He cannot walk, stand, sit up, or move great distances without assistance. Also, he has a weak trunk, so Nathan usually needs a supportive seat. In addition, he also has spina bifida, which is also known as myelomeningcoele. This is birth defect on which the backbone and spinal cord do not properly close before birth*2+. In Nathan s case, this caused partial paralysis of the legs and weakness of the hips, legs, and feet. Due to spina bifida, Nathan has hydrocephalus, where there is a buildup of fluid inside the skull. To remedy this, Nathan had an operation where the fluid buildup is drained to his bladder through a shunt for excretion. His parents also mention that he may have scoliosis due to his abnormal sitting posture. He tends to sit slanted. Also, Nathan tends to fidget a lot when seated. He also has the tendency keep his right arm high in the air, by his head. 13

15 To begin the optimal design of the wheelchair, the group found it imperative to see what other projects and products were fabricated in the past that had similar goals as this project. At the University of Connecticut, a team in the past year modified an all-terrain power chair to better suit the needs of their client. Various commercial all-terrain power chairs also exist, but as alluded to before, prices were very high. Also, patents were researched, two of which were related were filed in the late 1990s. They both encompass a unique power wheelchair design to travel on rough terrain. Next, the group created three alternate designs that would satisfy the requirements of the project. With these three unique designs created, the best aspects of all of these designs will be combined for this optimal design. Next, it was important to address the main aspects of what the family desired in the design. Since Nathan is capable of controlling his own movement, the family would like to have the power-chair be operated by Nathan. The team has decided to use a left-hand operated joystick. Also, the family has expressed the desire for an emergency override control, just in case Nathan is in danger. The power chair must also be transportable, so it must satisfy certain dimensions. The power chair must also be intuitive to use for anyone. For example, a person must be able to easily put Nathan into the wheelchair with ease and without damaging the device, which is a problem the family has run into with many assisted moving devices. Since Nathan is still young, the design must accommodate his growth. Another important objective for the power chair is to make sure that is safe for Nathan and anyone surrounding him. Having searched for various all-terrain power chair designs and having the group come up with three unique designs. The group combined all of the best aspects of the three designs for this optimal design. The optimal design also tried to address the family s requirements as best as possible. Two of the designs consisted of a six-wheel power chair instead of a four-wheel design for added safety. However, since the family desired that power chair must fit in their Honda Odyssey minivan, it was best to use a four-wheel design to conserve space. The added safety of having six-wheels would barely be helpful, since the power chair is being built for slow speeds under 5 miles per hour. This was one of the major physical aspects that the group needed to agree upon. Another aspect that will be implemented will be to use an extendable boom for the seat. This will allow the chair to be height adjustable, so Nathan can be more socially active in school with his peers and be at eye-level with his peers, when needed. Another aspect from one of the designs will be to use latching systems. This will allow for easy detachment of the chair and allow clear access to motors and batteries, stowed beneath, for maintenance reasons. All three designs agreed upon using a joystick to control the movement of the power chair. Also, all three agreed upon the importance of having a comfortable and supportive chair. The design will be implemented by analyzing the mechanical and hardware components, such as the frame/chassis and suspension. In addition, the possible electrical and software aspects will be discussed. Overall, the estimated cost will be $2,000. Some of the mechanical components include the use of a seat, which will provide him with his main support. The wheels used will also be large and provide ample grip. Anti-tip wheels will also be implemented. Electrically, the microcontroller will control most electrical aspects of the power chair. A 14

16 VR2 Joystick and module will also be implemented for easy control. There will be four DC motors to provide power to each of the wheels. Despite all of his conditions, his family has expressed that he is capable of operating a power chair on his own. Nathan is adept at using his left hand, so the power chair controls would have to be implanted for left-hand control. With many major aspects analyzed, the team hopes to design an allterrain power chair that Nathan will be able to use on all sorts of terrain in a safe and efficient manner Subunits The complete chair is made up of a number of smaller systems that come together to make the complete chair and its operation. Each of these subunits has to be designed so that it not only accomplishes its task, but also integrates into the complete system. The following section details the design of each of these subunits, and describes where they fit in the complete design. Figure 7 - Early CAD model 15

17 Mechanical Figure 8 - Prototype CAD model The mechanical components of the power chair encompass all of the parts that have a role in the structure and mobility of the device. These parts include the seat, arms, chassis, wheels, drive train, suspension, and seat actuator. The way in which each of these parts will play a role in the mechanics of the power chair is described below Seat The seat will be a very important part of the power wheel chair for the client. The seat must provide comfort and cushioning. The seat must also provide enough support for the client to have a safe ride. The seat will help correct the client s posture positioning close to an 80 angle. The seat will contain a cushioned headrest for added support and comfort. The seat will contain a positioning system set up to keep the client in the center of the chair along with a harness and seat belt. These will give the client the safety that he needs to ride around the trails. This position system will also allow for adjustments to be made as the client grows. The seat will be tested to see how it fits the client currently, and adjustments will be made so that it can be easily adjusted to fit the client as he grows Arm Rests The arm rests will provide the client will a place to properly rest his arms. The left arm rest will contain a joystick that will provide control of the wheel chair and all of its features. The arms will be adjustable, so they do not get in the way when the client is being placed into the wheelchair Frame 16

18 The frame of the wheelchair will be made from 6061-T6 2x2-inch square tube stock aluminum. This is a high-strength aluminum alloy, capable of being welded easily while regaining much of its strength in the weld area after a period of several weeks has passed. Therefore, it will be necessary to assemble and weld the frame of the chair as soon as possible. This will allow maximal strength recovery in time for delivery of the final product to the client. Testing of the frame well involve stress testing of the welds to ensure that they are within tolerances. This testing will have to occur later on in the construction of the chair. If the welds are tested too early, this will result in failure of the aluminum itself, as the heat of welding greatly reduces the strength in the metal for a temporary period of time Wheels The wheels must be sufficiently large and treaded to provide grip in a variety of situations, including sand. Therefore we would like to choose wheels that are 10 to 14 inches in diameter that can be operated at both a high and low pressure, with at least two inches of width per tire. Each wheel will need to have an axel through the connecting lever-arm with a gear on the axel. The wheels will all have rotary encoders attached to account for relative wheel spin, which will be used to calculate power distribution between the wheels in the case of wheel slippage. Wheels will be inflated and checked for leaks on a regular basis. Anti-tip wheels will also be used as an added precaution to prevent tipping of the power wheel chair on uneven terrain. 17

19 Figure 9 - Anti-tip wheels Figure 10 - Tire used for the power chair Wheel Mounts 18

20 Each wheel will be mounted on a lever arm with one degree of freedom. This each lever arm will have a mounting point in the center for a shock absorber to be attached to the wheel chair frame, a mounting point to the frame, a mounting point for a gear, and a mounting point on the distal end for a wheel. The front and rear lever arms will share respective thru-axels. The lever arms will ride on pressfit bearings and be capable of independent motion, despite sharing a common, non-rotating thru-axel. This common, non-rotating thru-axel will provide a great deal of stability for the lever arms, as they must carry the weight of the wheelchair. In order to test the wheel mount, the frame of the wheelchair will need to be built first. The springs will be attached to the lever arms without the wheels, and each lever arm will be checked for a proper range of motion as well as the capacity of the wheel arms and suspension to bear the weight of the frame Suspension The suspension for the wheelchair will require springs that can resist the mass of the wheelchair, plus the force of any extra shock. Ideally, the suspension will provide an underdamped response for the smoothest ride possible. Overdamped or critically damped suspension response to bumps would jostle the client and make travel uncomfortable. The suspension must also have sufficient travel to accommodate for potential obstacles the chair could encounter. A locking mechanism will prevent the suspension from moving when it is undesired such as during transportation or on sand. The suspension will be properly tested when the frame and lever arms are complete, but before any other parts go on the chair. We can test the estimated weight of the chair, motors, and other components safely to ensure that we have properly tuned the suspension in this way, without risk of damaging them Drivetrain Because each wheel will be on its own suspension platform independent of the chair and motors, a system to transfer power to the wheels must be devised that can move without breaking. The motors will be placed onto each lever arm, allowing for a very simple direct-drive power system. The motor rotational velocity will be lowered for the wheels via gear ratios, providing the maximum amount of torque while preventing the chair from reaching unsafe speeds. The motors will be controlled from PWM inputs from the microcontroller run through an H-Bridge. Testing of the motors will be conducted on an individual basis first to ensure that each rotates at the same velocity, then to ensure that the H-Bridge circuitry functions properly Handbrake The handbrake will be a mechanical stoppage device attached to both of the rear wheels. This will allow the client s family to securely stop the chair regardless of whether the motors are attached or 19

21 detached. The hand brakes will be operated from the push handles via mechanical brake cables found in bicycles. There will be latching mechanisms on the brake handles so the brakes may be secured. Testing the brakes will require activating them, and attempting to push the chair Harness The positioning system along with other constraints will be used to keep the client safely in the chair during operation The client s body has a tendency to lean to one side, so this positioning system will be used to correct this imbalance. The constraints will be used to keep the hips and torso aligned and upright while sitting in the chair. The client will also have a padded 5 point harness be used to keep them upright while operating the chair. This harness will go over the user s shoulders, around the waist, and clip in between the legs to prevent them from slipping out, or leaning forward Figure 11 - Five-Point Harness The electrical components will provide all the functionality for the chair. The electrical components include the microcontroller, joystick, power supply, motors, MP3 jack / audio circuit, woofer, rotary encoders, voltage regulator, DC-DC converter chip, killswitch, and H-bridge. 20

22 Electrical The electrical components will provide all the functionality for the chair. The electrical components include the microcontroller, joystick, power supply, motors, MP3 jack / audio circuit, woofer, rotary encoders, voltage regulator, DC-DC converter chip, killswitch, and H-bridge Microcontroller The microcontroller will be the central electrical component to the power chair. Without the microcontroller, no features save the audio playing capabilities would work. The microcontroller will operate off of a 9VDC supply of power, while the CMOS circuitry will run at 5VDC. The microcontroller will receive input from the joystick, the killswitch, and the hall-effect sensors. These inputs will be processed to account for direction and speed as determined by the joystick, and wheel slippage as determined by the hall-effect sensors. The outputs will be to an 8-channel H-bridge. The microcontroller and H-Bridge will be tested using a the built-in LEDs on the Arduino s developer board. Other testing could be conducted via LEDs on a protoboard. Proper wiring of the microcontroller outputs to the H-Bridges will be critical, and thus the two devices operating together will require a great deal of testing. Figure 12 Microcontroller Hall Effect Sensors 21

23 The Hall Effect sensors will provide sensory feedback from each of the wheels. These sensors will operate on a 5VCD rail, the same CMOS voltage the Arduino Mega uses. The sensors will be mounted to the axel of each wheel, and provide feedback to the microcontroller for control of wheel slippage. The Hall Effect sensors will be tested by calibrating with known rotational velocities to determine measurement error and signal noise Joystick/Module The VR2 Dual Attendant control system consists of a Joystick Module, Power Module and Dual Attendant Module. This allows the drive and actuator functions of the power-chair to be controlled either by the occupant, or by an attendant from another location on the power chair. Control is easily exchanged via a push-button, and the attendant can limit the maximum speed of the chair to a comfortable walking pace. The mode of operation, selected actuator and speed setting are all clearly indicated to the attendant by extra bright LEDs. The attendant also receives audible feedback for each successful button actuation. The joystick will also have a controller to control lights and other addition functions on the wheel chair that will make operation easy for the client and his parents. There will also be a kill switch that will cut all power to the motor for safety. Figure 13 - VR2 Joystick and Module Power Supply 22

24 The power chair will run off of one common 36V power supply. The power supply itself will consist of three high-capacity, rechargeable 12V lithium-ion batteries in series. One DC-DC converter will step the 36V input down to 24V. From the 24V rail, a Voltage Regulator will output 9V and 5V. The 9V output will be used to power the Arduino, while the 5V rail will be used to provide power to the Hall Effect sensors and the joystick. The 24V rail will supply power to the DC motors. To prevent voltage drop in the batteries as their charge is depleted from effecting motor performance, the DC-DC converter allow voltage to drain from the battery system without any effect on performance of the chair, until one battery is completely drained of voltage. This system regulates power fluctuations in the circuitry as well as provides a greatly increased runtime for the chair. Recharge time, voltage, and current flow will all be tested on the batteries using a variety of instruments and practical experiments. Figure 14 - Lithium Ion Batteries DC Motors Four DC motors will provide power to each of the wheels of the powerchair independently. Each motor will be a 24V linear-voltage DC motor. The DC motors will not operate at maximum voltage and current flow, as the chair will not be designed for speeds above walking. However, every component will be tested and engineered to withstand twice the anticipated current draw, as the fourwheel-drive system will potentially increase individual motors above our desired maximum current draw, in order to compensate for wheel slippage. Because four drive motors are being used as opposed to two, the required torque for each individual motor will be half that of conventional powerchairs to achieve the same linear velocity. 23

25 The DC Motors will be tested to ensure that they are in working order, and can provide sufficient torque to move the chair. The maximum, half, and quarter voltage rotational velocities will be tested, so that the mechanical linkages from the motor to the wheels may be adjusted to prevent the chair from achieving too high of a linear velocity, while ensuring sufficient torque to move the chair. Figure 15 - Wheelchair DC Motor DC-DC Converters One DC-DC converter will provide voltage for the two distinct circuit elements the control and feedback system, and the drivetrain. By stepping down the voltage from the batteries, the DC-DC converter provides smooth voltage flow, even as the batteries drain below 36V. Even as the batteries age and are no longer able to store a total of 36V, the DC motors will still operate at peak capacity for a greater period of time The DC-DC converter will be tested for proper voltage conversion. The DC-DC converter operating on the motors will be stress-tested for twice the maximally-anticipated current draw. 24

26 Figure 16 - DC-DC Converter Voltage Regulator One voltage regulator will be installed on the power chair to further step down the voltage from 24V. Voltage regulators ensure stable power flow and limit maximum voltage, while maintaining a high enough current-throughput to run several digital components off of one voltage line. Therefore, every digital component in our power chair can be run from one DC voltage rail from one regulator. Because this line will run off of one voltage regulator, the components will be protected from power spikes due to draw from other components as well as voltage fluctuations due to motor usage. Voltage regulators have the advantage of being small components, only the size of a protoboard-scale transistor. The voltage regulator will be stress-tested alongside the DC-DC converter. 25

27 Figure 17 - Voltage Regulator Killswitch The killswitch for the electrical system will be a physical switch. It will disconnect the 18V rail from the H-bridge, as well as send a 3.3V input signal to the microcontroller. This will allow the microcontroller to conserve power by ceasing output. Furthermore it will prevent the motors from receiving any power, thus preventing movement of the chair. A separate on/off switch will be used for the entire power system of the chair. The killswitch will require manual resetting. Testing of the killswitch will be a simple procedure of running the chair and activating the killswitch Audio MP3 Circuit The killswitch for the electrical system will be a physical switch. It will disconnect the 18V rail from the H-bridge, as well as send a 3.3V input signal to the microcontroller. This will allow the microcontroller to conserve power by ceasing output. Furthermore it will prevent the motors from receiving any power, thus preventing movement of the chair. A separate on/off switch will be used for the entire power system of the chair. The killswitch will require manual resetting. Testing of the killswitch will be a simple procedure of running the chair and activating the killswitch. 26

28 Figure 18 - Audio Circuit Woofer The woofer will be the second component of the audio circuit. A Dayton RS woofer will be used. This woofer is capable of delivering sound in a 20Hz-20kHz audio range. This is more than sufficient range for all applications. Because the woofer may be mounted on or near the headrest, the maximum volume of the woofer will be limited. The woofer will be tested both with actual audio and with a function generator. The function generator testing will allow us to ensure that the maximum audio range is being delivered, and delivered cleanly by the device. 27

29 Figure 19 Woofer Software Microcontroller Software The microcontroller software will be programmed in embedded C. Embedded C provides far more mathematical capabilities than assembly, while being far easier to code and test. Programming will be done in phases to ensure rapid development and testing for each of the components of the software. The first phase of programming will be the joystick input code. The XY map of the joystick will be assigned decibel values rather than linear values. This will provide a more natural feel to the wheelchair than simple linear velocity response. In other words, each point in either the X or Y direction of the joystick will result in an exponential increase in voltage to the DC motors. At this stage of software development, the microcontroller will be tested with an LED circuit only. The second phase will be to map these outputs to the H-bridge, and will allow for testing of the DC motors in conjunction with real or simulated joystick input. At this stage, mapping of the X coordinate on the joystick to relative wheel rotation will be complete, to allow the chair to turn. This stage will be tested with both LED circuit and the DC motors. At this stage, code will also be implemented to prevent jerky movement of the chair, smoothing out sudden changes in joystick position. The third phase of software development will be to use the data from the rotary encoders to adjust power distribution for relative wheelspin. Unlike the exponential mapping of the joystick, the adjustment for relative wheelspin will follow a logarithmic curve. In other words, for greater amounts of slippage on one or two wheels, the increase in power distributed to the remaining wheels is less than before. This will prevent over-torquing the remaining wheels on potentially loose terrain like gravel, 28

30 sand, or snow, and thus breaking traction with all four wheels instead of maintaining grip. This stage will be the most difficult to test, and will require a combination of software debugging, LED circuits, and real-world data gathering. The precise formula for calculating relative wheelspin depends on desired relative wheelspin (e.g. when turning, one pair of wheels may be spinning more slowly or in the opposite direction), actual wheelspin, and the aggressiveness of the response of the traction control. The mathematics for the software side of the project will require a great deal of focus and learning, to facilitate a proper application of an all-wheel-drive system in conjunction with safe powerchair operation. 29

31 2.2. Prototypes The prototype is based off of the optimal design that was discussed earlier. However, this section will go much more in depth of the various parts Mechanical The mechanical section will discuss a majority of the physical aspects of the power chair. Lower Frame Fabrication To start the mechanical fabrication, the base frame had to be made. The frame was made up of 2 x2 square aluminum tube. This required cutting the aluminum stock into two pieces that were 30 long and three pieces that were 21 long. In figure 20, below, the two horizontal pieces on the top are 30, and the three pieces placed vertically were 21. With this setup, this gives the base frame a length of 30 and a width of 25. This makes the power chair design large, with plenty of space to place various components that will be needed. It is important to note that these pieces were cut at about a quarter inch larger and then milled down on both sides to the proper size. This ensured that the edges would be smooth Figure 20: Lower Frame. 30 x25 Lower Frame Modifications Once the lower frame pieces were cut and welded together, as seen in figure 20, modifications were done to make provisions for attaching other components. It is important to note that the middle piece was not attached due to modification that took place in a later meeting with the client where it was originally planned that the piece would be support the rear portion of the seat. However, this was 30

32 not put in, and another system was devised to secure the rear portion of the seat, which will be discussed later. The seat base had to be attached in the front and rear. For the front, the purchased seat frame allowed provisions for a latching system. As long as there was a circular rod, the frame could detach from the frame simply by pushing on the latch. The optimal rod diameter was 7/16. Two 2 x2 aluminum square tubes were cut to two inches each. Holes a little larger than 7/16 were made in the center to allow the rod to go through on both sides of the tube aluminum to act as the support. These aluminum square tubes were welded onto the frame, so they would stay in place. Figure 21 shows the system. Figure 21: Seat frame attachment at the front After a meeting with the client, it was realized that the seat needed tilt further back than the team had planned. Therefore, the middle piece of the lower frame was removed to allow the seat to rest lower. The seat frame had two protrusions on the side of the seat, which rested well on the sides of the lower frame. Two pieces of aluminum at about 1.5 x1 x.5 were cut and milled. They were welded onto the frame at angle of 20º, relative to the frame. Once welded, the seat was placed onto the frame. Then, a quarter inch hole was drilled on both sides to allow it be screwed and bolted. This would allow for a relatively easy way to remove the seat when needed. In summary, the front latch would have to be depressed and the two bolts at the rear would have to be removed to remove the seat. This process is quick and easy. 31

33 Figure 22: Seat frame attachment at the rear, on the left side. The last modification made to the lower frame was in regards to making the holes for attaching the plexiglass box. Holes were made one inch and four inches from the rear on both sides of the frame, in the center. These holes were to be quarter inch in diameter and would correspond to the holes made in the plexglass box. The holes were made all the way through the tubing, so the holes would be present on both sides of the tubing. This would allow a screw to be put in from the top, and a bolt could be used on the bottom for securing the box. The plexiglass fabrication will be discussed later on. Figure 23: Holes for plexiglass box attachment Lever Arm Fabrication The next parts fabricated were the four lever arms. These arms would be mounted on the aforementioned lower frame via lever arm mounts, which will be discussed later. The ideal length was 32

34 determined to be 18. Similar to before, these pieces were cut from stock aluminum and milled down to make sure the length was accurate. Lever Arm Modifications There were two major modifications to make on the bearing arms. Once modification involved making holes and pockets for the bearings. The other modification that was needed was to make provisions for a motor mount, where the motor mounting plate would bolt onto. Bearing holes needed to be made in two locations on each lever arm, each on the opposite ends of the lever arm. The upper part of the lever arm utilized the Spyraflo bearing that allowed for a.5 axle to go through it, while the lower part of the lever arm utilized a Spyraflo bearing that allowed for a.75 axle to go through. Regardless of the axle diameter, both bearings had the same size footprint, so the holes and pockets made for either bearing were exactly the same. Figure 24: Bearing mount Figure 25 shows the scaled drawing of the locations of the holes for the bearings. The bearing was placed on the graph paper, and the holes were marked. The centers were found from this sketch by measuring the center from the top left corner. The coordinates were entered into the milling center and the holes were drilled with drill bit of the respective radius. For the center hole, a pocket program was made to create the hole, since there was not a drill bit large enough to make this hole. A 9/16 end mill was used to create the pocket with a radius of.825 Please note that in figure 25, the center hole shown was smaller than the actual hole that was made. All of these holes were done on all four lever arms, on both sides. Therefore, this procedure had to be repeated eight times. It is important to note that a practice run was done first to ensure the coordinates were accurate. Table 1: Coordinates for bearing holes 33

35 Holes X-coordinate in inches Y-coordinate in inches Radius in inches Top Center Bottom The following is the code used on the milling machine to create the center hole: X center abs Y center abs Radius.8250 CCW Tool Offset Left Fin cut Feed rate 3.0 Tool=.01 Figure 25: Scaled drawing of bearing hole positions. One square is.25 x.25. With calculations in regards to chain length to the wheel sprocket, four holes were made on the lever arms that would correspond to the motor mounts, which will be discussed in the next section. The holes were made at the following coordinates, with respect to the upper corner of the lever arm. Table 2: Coordinates for motor mount holes on lever arm Holes X-coordinate in inches Y-coordinate in inches Radius in inches

36 Motor Mounts Four motor mounts were fabricated. The first step that was done was to make the holes that lined up with the four holes on the lever arm. Each mount measured 5 by The holes were made with respect to the top, left corner, in figure 26. The hole coordinates are as follows: Table 3: Coordinates for motor mount holes, attaching to lever arm Holes X-coordinate in inches Y-coordinate in inches Radius in inches A B C D Figure 26: Scaled drawing of motor mount holes. One square is.25 x.25. Next, the actual holes for mounting the motors were made below where the previous holes were made. Holes 1, 2, and 3 used a drill bit that allowed provision for 10x32 machine screws. A pocket was also made to allow for the motor gear to protrude. The diameter of the hole was one inch. The coordinates of the holes are as follows, noting that the coordinates are with respect to the O at the bottom right of figure 26: 35

37 Table 4: Coordinates for bearing holes Holes X-coordinate in inches Y-coordinate in inches Radius in inches x32 drill bit x32 drill bit x32 drill bit Center Lastly, with respect to the O on the lower, right corner, 3 inches were milled, going left in figure 26. About half of the motor mount was milled off to make it thinner, allowing for more clearance for the chain to rotate around the protruding motor sprocket. This made the width of this portion about.25. The finished mount can be seen in figure 27, noting that the milled off portion is mounted so it is facing the outside of the power chair. Figure 27: Motor mount. View from under the power chair. Lever Arm Mounts In total, eight lever arm mounts were fabricated. The pieces were 3.25 x1.5. A hole with a.5 diameter was drilled through, with the center being.5 form the bottom. At the top, one inch was placed on the lower frame to allow for the piece to be welded on to the frame. The mounts were placed, so the center of the piece was 8.5 away from the closest edge of the power chair frame. Figure 28 shows the placement of the lever arm. 36

38 Figure 28: Lever arm mount Upper Spring Mounts In total, eight upper spring mounts were fabricated. The pieces were 2.25 x1.5. A hole with a 5/16 diameter was drilled through, with the center being.5 from the bottom. Also, the aluminum stock that was originally.5 thick was milled entirely, so it would be only.25 thick. At the top, one inch was placed on the lower frame to allow for the piece to be welded on to the frame. The mounts were placed, so the front edge lined up exactly with the closest edge of the power chair frame. A one inch spacer was placed in between the mounts, on the center of the frame, to allow for proper placement for welding. Figure 29 shows the mounting location and fabricated piece. 37

39 Figure 29: Upper spring mount Lower Spring Mounts The lower spring mounts were created by cutting aluminum stock that was.25 thick to 1.5 by 1. It was cut and milled for proper size. A 5/16 hole was made in the center of the piece at the coordinate (-.75,.-5), relative to the top, right corner in figure 30. Eight pieces like this were made. Then, pairs were assigned to which arm they would go to. Either the front, right,or front, left, etc. This was important because the top most corner was cut off at a 45ºC angle to allow for better rotation of the shock. Then, a one inch spacer was placed in between the pair of mounts, dead center, on the top of the lever. The pieces were then welded in place. 38

40 Figure 30: Lower spring mount. Footrest mount For mounting the footrest, an aluminum piece of dimensions 8 x1 x.5 (LxWxD) was used. From the width, 1/16 was milled off. The depth was cut in half to.25 by milling, as well, for the 7.5. About.5 in length was kept at.5 in diameter, so it would lock into the foot plate. Making these alterations allowed for the piece to fit in the slot in the foot plate. Lastly, two holes were made from the top to allow for mounting on to the frame. The coordinates were (.5, -.5) and (.5, -1.5), with respect to either the top left or right corner that was milled. The drill bit used was a.25 in radius. Once mounted onto the foot plate, the aluminum piece was held in place and the holes were marked with a hole punch. Then a drill was used to drill all the way through the square aluminum tube to the other side. This allowed a system to be made, where the fabricated aluminum piece could be bolted onto the lower frame. Figure 31: Left: Mounted foot plate. Right: holes in front of the lower frame 39

41 Lever Arm Axles The lever arm axels hold the lever arms in place. They were created from half-inch diameter aluminum round stock and lathed to the proper length. Both ends of the rods were threaded by hand using a half-inch/13 threading die. Wheel Axles The wheel axels started as.65-inch round aluminum stock. The stock was cut and lathed to a length of 5.25 inches. This stock was then lathed down to a diameter of.53 for two inches on one side. The smaller diameter would allow the stock to fit into the wheels purchased at NEAT marketplace. The bearings purchased for the lever arms have an inner diameter of.65 inches, so the rest of the bearing was left at its original length. Once the diameters were properly lathed.25 holes were drilled on either end of the axels. Threading was then placed into the holes to allow screws with washers to secure the wheels and sprockets in place on the axels wide slots were milled into both ends of the axels. These slots are for the mounting of keys from the sprockets and wheels and allow the motors to drive the wheels. Gears and Chains The motor required a chain size #25. This naming scheme indicates a pitch size of a quarter inch, meaning that each link was a quarter inch away from the next one. It was determined that the chain length had to be two feet long to fit around the wheel sprocket and motor sprocket. The amount of teeth on the motor was nine. The amount of teeth on the wheel sprocket was 30. This allowed for a 30:9 gear ratio. The ratio was determined mathematically to limit the speed of the chair to walking speed when the motors run at the decided highest voltage. Only one link from each chain had to be removed with a chain breaker to provide proper tension. 40

42 Armrest Figure 32: Chain mounted to motor and sprocket. 41

43 Figure 33: Arm rest design (left) and implementation (right). The armrests were designed to be height adjustable. Two pieces of aluminum that had the dimensions 16 x 1 x.5 (LxWxD) were cut and milled as necessary. From the top, one inch down in the center, quarter inch holes were drilled. Five more holes were made, each an inch lower than the previous one. The holes were also threaded. Another piece of aluminum was prepared to have the holes line up with the piece fabricated before. Rectangular tube aluminum that had the outer dimensions of 16 x1.5 x1 was prepared so two piece were available. This top piece would ideally slide on top of the previous piece, which would be welded to the frame, the holes made in the pieces would line up with the other piece, so both can be screwed and welded. The six holes were made in the same manner as before; however, the first hole was made 3 inches down from the top instead of only one inch. This piece was designed to rest on the lever arm at the lowest setting. The thinner piece would be welded with two inches on the lower frame. Figure XX shows the first piece (lower) and the second piece (upper 42

44 piece). The lower pieces were welded on to the lower frame, 5.25 from the front of the power chair. Two inches of the piece would be welded onto the frame. Figure 34: Left: height-adjustable arm rest. Right: Scaled drawing of arm rests. Below: drawing of arm rest part. One square is 1 x1. Next, pieces were fabricated that would be welded onto the upper tube aluminum. Two pieces from the rectangle tube aluminum stock was cut into 3 inch pieces. In the center of the piece, from the top, holes were made at.5, 1.25, 2, and 2.75 down with a quarter inch drill bit. The same procedure was done to four pieces of aluminum with the dimensions 4 x1 x.5 (LxWxD). The coordinates for the holes can be seen in the following table. The following diagram shows the scaled drawing. Table 5: Coordinates for arm rest holes Holes X-coordinate in inches Y-coordinate in inches Diameter in inches 1.5 (.75 for tube) (.75 for tube) (.75 for tube) (.75 for tube) Once all the pieces were fabricated, further welding was done. First, bottom of the 4 piece was welded to the top of the larger rectangular tube aluminum, at 90ºC. This was done to another piece, as well. Then, two 10.5 rectangle tube aluminum was cut and milled to size. Then, the two other 4 piece was welded 90º to the large piece, as well. The three inch tube aluminum was welded onto the 10.5 tube aluminum, as shown below. Velcro was placed on the horizontal surface to attach padding. At the end of the armrest, black containers were bolted on by drilling two quarter inch holes and making sure they lined up with the four inch piece. The left container houses the joystick, while the right container can store belongings. Figure XX shows the final assembly. 43

45 Figure 35: Arm rest assembly and arm rest padding Headrest Mount On the back of the rear seat rest, four screw holes were found to allow for mounting a headrest. Since the headrest being used did not attach readily to the seat, fabrication needed to be done to allow attachment. The holes on the seat were mapped out to see the distances relative to each other. On a piece of square tube aluminum with the following dimensions: 5.5 x2 x2 (LxWxD). Holes were made according at the coordinates listed in the table, with respect to the top, left corner. Table 6: Coordinates for arm rest holes Holes X-coordinate in inches Y-coordinate in inches Diameter in inches Next, the hole for allowing the headrest rod to go through needed to be made. The square rod was a little larger than.25 x.25. Using the smallest end mill available, a square of a little larger than this was milled out on both sides of the square tube, in the center of the mount, with respect to the sides. Figure XX shows the final fabricated piece. 44

46 Figure 36: Headrest mount Plexiglass Box The plexiglass was made to ensure that all the electrical components fit inside and would be kept from getting wet. Also, a custom box would make the box seem like it actually fit in with the design of the power chair. There were two thicknesses in plexiglass available. One was.25 thick, and another one was of unknown thickness since it was donated. It was thinner. From the thicker plexiglass, three pieces of dimensions 30 x8 were cut. Two pieces with the dimensions 7.6 x7.6 were cut. Lastly, from the thinner plexiglass, a 30 x10 piece was cut. This would be the lid, which would be attached by hinge system. The pieces were glued together. The large thick piece served as the base, while the other large pieces were glued on top of it, on the long edges. The squares were glued in between the two large pieces to form the box. The base piece had holes with a diameter of a quarter inch drilled through to line up exactly with the ones already drilled on the lower frame. This would allow the box to be secured to the frame. The following image shows the complete box. 45

47 Figure 37: Plexiglass box Seat Modifications The original seat purchased from N.E.A.T. Marketplace had a large rear seat support. The team desired to use a tighter and more supportive back support for Nathan. Therefore, the original rear seat support was removed, and replaced with a smaller one. The switch was simply because the mounting brackets lined up exactly with the screw holes found in the new rear support. Figure 38: Left: Old rear seat support. Right: New rear seat support. 46

48 Mounting Springs Once all the lever arms were put in place and the spring mounts welded on, the springs could be attached. The springs had built in bearings that allowed for a 5/16 screw. Two 2 screws were used for each spring, for the attaching to the upper and lower mounts. They springs were then bolted into place. Wheels With the keys placed in each wheel, the wheels were put into the wheel axle. Once on, the axle was put through the wheel axles. Once through, the sprocket with the key was put in to stabilize the axle. For full stabilization, a.25 x20 screw that was.5 in length with a one inch was washer was screwed on to each side of the axle to conceal the axle and limit movement. This process was done for all four wheels. Figure XX shows the mounted wheel. Figure 39: Mounted wheel. Harnesses The seat came with a two-point buckle; however, it would be ideal to have a four-point harness for further constrain when needed. There were many screw locations on the rear of the seat. The four point harness screwed in easily at the various points on the rear. The following image shows both harnesses. 47

49 Figure 40: Harnesses. Chain Guards For further safety, it was necessary to guard the chains from any objects that may have come in the way. Chain guards were fabricated from four aluminum sheet metal, sized at 12 by 11 inches. Using a clamping device, 90 degree corners were made, so it could attach to the lever arm. Off of the lever arm, a raised bump was made to accommodate the height of the sprocket. From here, it bent down again to actually cover the chains. The following figure shows the final product. 48

50 Figure 41: Chain Guard Electrical Joystick The joystick used for our wheelchair is a potentiometer-based dual-axis joystick. When supplied with a 5V source the joystick puts out 2-3V with a neutral voltage of 2.5V. Joystick amplification circuit The joystick amplification circuit receives three supply voltages and two variable input voltages. The three supply voltages are 12V, 5V, and 19.6V. The 12V supplies are used for a voltage divider with resistors of [values]. This divider produces a 10V theoretical output. The 19.6V supply is used to power the two operational amplifiers and the two differential amplifiers. The operational amplifiers are noninverting and set up to have an amplification of 5. The differential amplifier receives an input from the 10V voltage divider on the inverting input and the outputs of their respective op-amps on the noninverting input. This subtracts 10V from the output of the op-amps. The math becomes for the lowest value on the joystick, for the nominal value of the joystick, and for the maximum output of the joystick. The 5V supply is used to supply positive voltage to the joystick. 49

51 Figure 42: Above: Amplification Circuit. Below: PCB Design 50

52 Motor Controllers The motor controls come from Poloulo, a specialist in motor controller technology. By using a commercial motor controller we can have controllers designed for the relatively high voltage and very high current required to drive the motors of the wheelchair. These motor controllers also take a simple PWM input, a digital directional control (hi/lo), and can output fault signals for error debugging with a microcontroller. DC-DC Converter The DC-DC converter takes 36V-20V as an input and converts it down to 12V with up to 29.1A of current. This supply is sufficient for driving the voltage of our motors while supplying up to 7A of current to each motor. CAD A lot of planning had went into the design. Therefore, the computer-aided design was made to get a better idea of what was going to be built. Figure 43: Actual versus CAD Design comparison 51

53 3. Realistic Constraints When designing a self-powered product for a handicapped patient, there are many restrictions that must be addressed. It is important that these constraints are recognized, so the product can operate as well as possible under the circumstances Physical The wheelchair must be made to fit in the doorways of the house, which are a minimum of 36 inches wide. The maximum height of the wheelchair must be collapsible to 40 inches, with an overall length of inches. Because the family does not currently own a collapsible ramp for their minivan, the wheelchair must be light enough for the father and/or mother to lift into the van by themselves Economic Economic constraints are a major concern for the production of powered wheelchairs in general. Un-powered wheelchairs designed for special needs individuals can run as high as eightthousand dollars. Most of these costs are production related and not materials-related. Because these wheelchairs tailored to the needs of individuals, costs are kept high. Fortunately, most families do not need to pay these costs directly, as health insurance is a mitigating factor. Powered wheelchairs increase the price drastically, especially if the wheelchair is designed for outdoors use. These wheelchairs can vary in price from $14,000 to over $18,000 and are likely not covered by health insurance. Being able to produce a wheelchair that is both cheap to construct and cheap to maintain will be key in supporting Nathan, and Nathan s family. This project, specifically, has a set budget, which cannot be increased. The only way to increase group spending is seek out organizations that will donate money or companies that will donate parts. Seeking donations and free parts will be imperative to building a quality all-terrain power chair Environmental The environmental impact of our device will also be very important. While this is an all-terrain wheelchair, it will be important that the device does not destroy the environment it was created to allow Nathan to enjoy. The use of electrical components as opposed to the gas-powered equivalent means that virtually zero harmful emissions will be produced. Most obviously, it will produce heat. Disposal of the batteries to power the device could also potentially produce a negative environmental impact due to the corrosive and toxic materials that are contained in batteries. Also, all of the electrical components could damage the environment. These other components must be handled with care and disposed of properly when the time comes. Educating the family themselves on how to dispose of the power source and various components will be important in delivery of the product. Even though the power chair will have minimal impact on the environment, the environment might impact the power chair. The power chair will need to be stored in an indoor environment. However, due to the nature of the power chair, it must be able to operate in rain, snow, and other types 52

54 of weather, to a certain extent. It has to be durable enough, so the power chair will not be experience failure in outdoor conditions. All of the components must be covered and waterproofed Sustainability Sustainability of this device is paramount. The family wishes to be able to use the device for years to come. Thus, the wheelchair must be robust enough to go over backwoods trails with minimal maintenance. Being able to adjust the wheelchair for Nathan as he grows is also important for sustainability of the device. Furthermore, because this is a power wheelchair, management of the batteries, specifically their disposal, longevity, and charge-capacity are important issues. The deep cycle batteries that will used can be charged with a charger. Therefore, it will not be necessary to replace the batteries all the time. Also, if one of the components ends up failing, it must be easily replaced. Lastly, since this will be used in the outdoors, any dirt, mud, and water must be easy to remove to prevent corrosion and damage to critical components Manufacturability The manufacturability of this wheel chair is also important to its sustainability. If the design were put into production, then to fulfill its purpose of being a cheap, safe alternative to other powered all-terrain wheelchairs for special needs individuals, then ease of construction, selection of cheap materials, and a modular construction will be important. Modular construction will allow the individuals to tailor the wheelchairs to their specific needs and wants, while reducing price drastically. For example, every part will not need to be custom-made for the individual but can be premade in bulk Social The social implications for this wheelchair are another very important constraint. The wheelchair should not produce excessive noise. The interface should be intuitive, and the restraint system should be easy and obvious to operate. The speakers should not be so loud that neighbors or passers-by are disturbed. Furthermore, the power chair will be made to bring Nathan closer to eye level with the chair attached to an extendable boom. It will increase his capacity to be social and enjoy the outdoors with others Political and Ethical The political and ethical constraints of this project are some of its guiding principles. The wheelchair should not put Nathan into unsafe situations via its design. For example, the motors should not be capable of allowing Nathan to operate the wheelchair at unsafe speeds, especially considering the nature of backwoods trails in New England. Manufacturing this product has the political impact in creating a device that is affordable to families and individuals with these special needs and a desire to enjoy the outdoors and be more mobile. As a cheap alternative, the device could provide mobility to those who may not have health insurance or would be otherwise unable to be self-mobile Engineering Standards 53

55 This all-terrain power chair will be designed to meet the standards used in power chair development. It will implement advanced electronics and quality material that will best suit the requirements of the family. It will maintain speeds similar to that of most power chairs, which is around 5 miles per hour. All of the members will have undergone training in the machine shop by the time of the fabrication of the power chair, so top quality craftsmanship will be implanted when the parts are being made and put together. 54

56 4. Safety Issues The safety of the device for the client s use is the number one concern in its design. The mechanical and electrical components of the power wheel chair can cause the most concern for the client if not properly built. All components of the wheel chair will be properly tested to insure that the device is safe for use Mechanical The mechanical components of the power wheel chair involve the most safety. The power wheel chair must be very stable to withstand the rocky, uneven terrain it is meant to endure. A solid chassis and larger wheels are to be used for maximum stability. The chassis must be a solid build to support the weight of the power wheel chair and the client. If not properly built and tested, the chassis may break during operation, causing possible injury to the client. The wheels must be able to withstand the terrain that the power wheel chair may travel through. The wheels must be properly attached to prevent a wheel form falling off during operation. If a wheel were to fall off the client may face serious injury which may cause the power wheel chair to lose stability and fall over. The power wheel chair must be able to keep the client secured in place during operation. Constraints and a five-point harness will keep the client sitting a position close to 90 while in use. The constraints will feature a position system that will be adjustable and allow for the client to be securely seated with a tight fit, to prevent any movement during operation. The seat of the power wheel will be able to be adjusted to allow for someone to easily place the client within the wheel chair. This will put less strain on the parents of the client or whoever is assisting the client. The suspension must be able to absorb contact, to make for a smooth ride that will not cause any damage to the client. Too much contact with bumps may cause damage to the clients back as well as discomfort during use Electrical In terms of the electrical components, all wires are to be covered to prevent any shorts or accidental exposures that can cause a malfunction in operation. The battery will also be covered. In a worst case scenario, a kill switch will be used that will shut down all power to the power wheel chair, which is an addition safety feature. In case of total power failure, the power wheel chair will also feature pegs on the back that will allow for it to be pushed or pulled. This will also make transport of the wheel chair easier. Addition safety features will include a set of led lights that will allow the client to see if he ever were to ride in darker light or as a way for the client s parents to know exactly where he is at all times. A small horn may also be added for the client to inform their parents if they are in need of assistance or if someone is in the way of his power wheel chair. 55

57 5. Impact of Engineering Solutions The impact of this powerchair design could be quite significant. As it is a cheap, lightweight, and modular design capable of providing mobility in a variety of settings to disabled persons, the societal impact could be perhaps the largest, and most important. Such a solution to the problem of mobility in a variety of terrains will, however, inevitably have an impact in global, economic, and environmental contexts as well. The environmental impact of the powerchair should be minimal compared to other off-roading devices. Because it is battery-operated and rechargeable, the carbon footprint of each chair during operation should be lower than if it were gas-powered. Furthermore, the batteries to be used in this design are not lead-based, and are acid-free. Disposal of the batteries is less hazardous than that of lead-based batteries, with less potential environmental damage if one were to leak. By using a common, cheap, and lightweight metal such as aluminum for the frame of the wheelchair, less power is required to move it and less of an environmental impact is made in the obtaining of the metal itself. The lighter weight of the design reduces transportation fuel costs and thus the carbon footprint of the device. The largest potential impact of the power chair is through direct environmental damage. For example, driving over plants and disturbing ecological niches. However, this is to be expected for all outdoors activities, and it is up to the operator and operator s family to minimize such damage. On an economic scale, producing a cheap and easy-to-use, safe power chair presents a great deal of economic potential. While most such power chairs are quite expensive and since they are not covered by insurance, a cheaper alternative provides outdoors access to individuals and families who may not be able to otherwise afford a means to enjoy the outdoors. Furthermore, cheap production of the design and easy manufacturability means new production jobs. Combined with the relatively low price, such a design has great growth potential in a market that is currently untapped due to priceexclusivity. The global impact of such a design has the potential to be very broad. Besides the creation of new jobs in relation to the production of such a chair, the low environmental impact combined with a large social impact means that such a chair could be life-changing for a great many disabled persons and their families across the globe. The societal impact of such a cheap, available, and safe chair is the largest and most meaningful involved with the design. Families that would otherwise be unable to enjoy the outdoors as a whole may now explore together, with each family member capable of self-direction. It removes from the family and the user the dependence on one another for mobility in the outdoors. In the particular case of the client, by raising him up to eye level with the height of the seat, the chair provides a greater social impact for the client. He may now feel more normal, and others can now converse with him without having to kneel or look down. This provides a greater capacity for the client to socialize, increasing his overall happiness. 56

58 6. Life-Long Learning Many new skills were and will be used in the production of the all-terrain power chair. The skills learned will be carried with the group for the rest of college and beyond Social The first part of project incorporated the sharpening of the groups social skills. The members learned more about each other and their respective goals. Once this was done, the group had to immediately meet the client and family. The members had to interact with the clients and better understand their desires. Due to the nature of group projects, teamwork was essential. All tasks were divided as evenly as possible, with respect to the person s expertise. Communication skills were also improved greatly, since the members had to always keep in contact with each other. Not only did the group have to keep in touch with each other, they also had to keep in communication with the clients to make sure the group was addressing all requirements. In addition, the group had to keep in contact with everyone who helped in building the project and ordering the components for it Educational Since the group is working with a client with disabilities, the group became more knowledgeable about various medical conditions. The group also learned how to create and prepare elaborate presentation on the project. The group also learned how to create order forms Mechanical The mechanical aspect of the all-terrain power chair was where the group had learned a lot. The group first had to learn the basic aspects of powered wheelchairs. Only with a good idea of the design of the power chair could the group even think about designing a custom power chair. Some of the key components that needed to be learned about were the motors and the joystick. For the electric motor, it was important to understand how to ideally utilize the power efficiently. Learning proper gearing ratios and how to even connect the gearbox to the wheels were essential. For the joystick, it was important to learn how to program and implement it to be easy-to-use. Also, it was important for the group to learn how to use tools and various power equipment. The group had underwent machine shop training to become better acquainted with the most commonly used power tools and machines. In addition, the group gained practice soldering by building an EKG kit. The group learned how to weld and cut various metals in a precise manner. With all of this training and actually building the power chair, the group greatly increased their mechanical skills Software The group had to become familiar with many programs. In building the EKG kit, the group had been refreshed on how to use LabVIEW, which all group members learned for two semesters. For initial 57

59 design, it became essential to learn how to use Solidworks, a CAD program that allows for 3-D modeling to better simulate the mechanical components. Creating these images was imperative to putting all the components together as planned. Lastly, the group became more familiar with programming in embedded C language for the PIC microcontroller and joystick. 58

60 7. Budget and Timeline 7.1. Budget The parts listed in table one are most of the major components that were purchased throughout the semester. The allotted budget was $2,000. As one can see, the team spent close to $2,100 with extra funding. There was a design problem that could not be fixed in the 4-layer PCB design, so motor controllers needed to be purchased to remedy the problem, causing an overshoot in the allotted budget. Regardless, the cost of the power chair that was built was much cheaper than most commercial products available and is far more versatile than many of the products. Table 1: Parts Units Price Total Price 24 Volt 120 Watt Electric Scooter DC Motor IC Driver (H-Bridge) DC DC Converter 360W Aluminum Extruded Rectangle 6061 T6 24" (.5"x1.5") Aluminum Square Tube 6061 T6 96" (2"x2"x.125") Aluminum (Refer to Order 6) Aluminum (Refer to Order 8) Used Seat with backrest Wheels and Assembly /8" Rear Suspension Shock Absorber Arduino microntroller Li-ion batteries w/ charger V Voltage Regulator V Voltage Regulator Heatsink Mp3 audio circuit Woofer Joystick Footrest, headrest, five-point buckle HEATSINK PWR DUAL BLACK TO layer PCB Layer PCB Motor Driver 15A IC LATCH HALL EFFECT 3-SIP HF3-500-N (Lever arm bearing) HF3-750-B (wheel axle bearing) Miscellaneous costs, including small purchases, shipping charges, and taxes 400 Total $

61 7.2. Timeline Task Name Duration Start Finish Task Leader Milestones 1 day Wed Wed 11/3/10 11/3/10 Start 1 day Wed 9/1/10 Wed 9/1/10 Proposal Presentation 1 day Mon 10/4/10 Mon 10/4/10 Alternative Design Reports 1 day Fri 10/15/10 Fri 10/15/10 Submit Project Schedule 1 day Wed Wed 11/10/10 11/10/10 Design Report & Presentation 1 day Wed Wed 11/10/10 11/10/10 Final Report & Presentation 8 days Wed 12/1/10 Fri 12/10/10 Project Completion 128 days Wed 11/3/10 Fri 4/29/11 Scheduled Team Meetings 4.25 days Mon 11/8/10 Fri 11/12/10 Reoccuring Meeting on Mondays 2 hrs Mon Mon 11/8/10 11/8/10 Reoccuring Meeting on Wednesdays 2 hrs Wed 11/10/10 Wed 11/10/10 PA, MC, MK PA, MC, MK Reoccuring Meeting on Fridays 2 hrs PA, MC, Fri 11/12/10 Fri 11/12/10 MK Parts Acquisition/Management/Queries 6 days Fri 11/5/10 Fri 11/12/10 Update & Submit Part Order Forms 1 day Fri 11/5/10 Fri 11/5/10 PA, MC, MK Update Parts List (1.2) Based on donations from Neat 1 day Marketplace Sat 11/6/10 Sat 11/6/10 PA Contacted motor vendor for specification sheet 0.5 hrs Sat 11/6/10 Sat 11/6/10 PA Contact various Craiglist sellers for low cost/free power chair 3 hrs Sat 11/6/10 Sat 11/6/10 PA Update Parts list (1.3) based on team meeting 1 hr Mon Mon 11/8/10 11/8/10 PA Create & Submit Part Order Forms 1 day Fri 11/12/10 Fri 11/12/10 PA Contact Client and Various Companies 1 day? Wed 9/2/09 Wed 9/2/09 Visit Client 4 hrs Sun 9/5/10 Sun 9/5/10 PA, MC, MK Visit Neat Marketplace 2.5 hrs Sat 11/6/10 Sat 11/6/10 PA, MC Contact Client on Project Updates 0.5 hrs Wed 9/2/09 Wed 9/2/09 PA Contact Client on Project Updates hrs Mon Mon 9/27/10 9/27/10 PA Contact Client on Project Updates hrs Mon Mon PA 60

62 Contact Client on Project Updates 4 Reoccurring event: Contact Client on Project Updates Biweekly Wesbite Maintenance Upload & Organize documents Team maintenance Maintain outgoing and incoming s 0.5 hrs 0.5 hrs 1 day? 1 day 1 day 1 day 10/18/10 10/18/10 Mon Mon 11/8/10 11/8/10 Mon Mon 11/22/10 11/22/10 Wed Wed 11/3/10 11/3/10 Wed 11/3/10 Wed 11/3/10 Wed 11/3/10 Wed 11/3/10 Wed 11/3/10 Wed 11/3/10 CAD Design 11 days Fri 11/5/10 Fri 11/19/10 Initial design 6 days Wed Wed 10/13/10 10/20/10 CAD Lower frame 13 days Wed 11/3/10 Fri 11/19/10 Lever Arm Wheels Component box Foot rest and misc. parts 13 days 3 days 3 days 72 days Thu 10/21/10 Wed 1/19/11 Wed 1/19/11 Thu 10/21/10 Mon 11/8/10 PA PA MC PA MK Fri 1/21/11 MK Fri 1/21/11 MK Fri 1/28/11 MK CAD - Upper frame 1 day Fri 11/5/10 Fri 11/5/10 Headrest 6 days Sun 2/20/11 Fri 2/25/11 MC Restraints 6 days Sun 2/20/11 Fri 2/25/11 MC Left Arm rest with joystick controls 6 days Sun 2/6/11 Fri 2/11/11 MC Right Arm rest 6 days Sun 2/6/11 Fri 2/11/11 MC Speaker location 6 days Sun 2/6/11 Fri 2/11/11 MC Seat Finalize CAD Design Microcontroller Opening and Setup 13 days 7 days 56 days 1 day? Thu 10/21/10 Mon 11/22/10 Wed 11/18/09 Wed 11/18/09 Mon 11/8/10 Tue 11/30/10 Wed 2/3/10 Wed 11/18/09 Learn how to program microcontroller 6 days Sun 1/16/11 Fri 1/21/11 MK I/O Programming 35 days? Sun 1/16/11 Fri 3/4/11 Basic & Advanced I/O Programming 6 days Sun 1/16/11 Fri 1/21/11 MK Simulate motor control 13 days Wed Fri 2/11/11 MK MC MC & MK 61

63 1/26/11 Test with actual motors 10 days Mon 1/31/11 Fri 2/11/11 MK Feedback Programming 11 days Fri 1/21/11 Fri 2/4/11 MK Simulate Feedback Controls 25 days Mon 1/31/11 Fri 3/4/11 MK Test feedback with actual motors 10 days Mon 2/7/11 Fri 2/18/11 MK, PA, MC Check compatability with power supply 5 days? Mon 2/21/11 Fri 2/25/11 MK Construction of Individual Parts 51 days? Fri 1/21/11 Fri 4/1/11 Welding practice 2 days Tue 1/25/11 Wed PA, MC, 1/26/11 MK Weld lower frame 11 days Fri 1/28/11 Fri 2/11/11 PA, MC, MK Modify upper frame 16 days Fri 1/21/11 Fri 2/11/11 PA, MC, MK Lower Frame 1 day? Fri 1/21/11 Fri 1/21/11 Lever Arm Construction (4) 3 days Thu 1/27/11 Mon 1/31/11 MK Lever Arm Mounts 20 days Mon 1/31/11 Fri 2/25/11 MK Component Box 21 days Sun 1/30/11 Fri 2/25/11 PA Seat mount alignment with chair 2 days Fri 2/4/11 Mon 2/7/11 PA Foot rest 3 days Mon 2/7/11 Wed 2/9/11 PA Upper Frame Modifications 26 days Fri 1/21/11 Fri 2/25/11 Seat base 2 days Fri 2/4/11 Mon 2/7/11 MC Head rest 13 days Wed 2/9/11 Fri 2/25/11 PA Push bars 6 days Fri 1/21/11 Fri 1/28/11 MC Create screw holes/slots in parts for attachment 12 days Thu 1/27/11 Fri 2/11/11 MK Combining Parts 49 days Tue 1/25/11 Fri 4/1/11 Lower Frame + Lever Arms 49 days Tue 1/25/11 Fri 4/1/11 MK Lower frame + motor box 45 days Mon 1/31/11 Fri 4/1/11 PA Lower frame + foot rest 45 days Mon 1/31/11 Fri 4/1/11 PA Lower Frame + seat assembly 45 days Mon 1/31/11 Fri 4/1/11 MC Upper frame + arm rests 45 days Mon 1/31/11 Fri 4/1/11 PA Upper frame + push bars 45 days Mon 1/31/11 Fri 4/1/11 PA Upper frame + headrest 45 days Mon Fri 4/1/11 PA 62

64 1/31/11 Mount shocks to lower frame + lever arms 44 days Tue 2/1/11 Fri 4/1/11 MK Create gearing system for motors 30 days Mon 2/21/11 Fri 4/1/11 PA Create waterproof vital component box 36 days Sun 2/13/11 Fri 4/1/11 PA Implement gears 30 days Mon 2/21/11 Fri 4/1/11 PA Sand rough aluminum surfaces 26 days Sun 2/27/11 Fri 4/1/11 PA Paint aluminum surfaces 23 days Wed 3/2/11 Fri 4/1/11 PA Electrical 76 days Wed 12/22/10 Wed 4/6/11 Power supply 25 days Mon 2/14/11 Fri 3/18/11 Power Supply test 25 days Mon 2/14/11 Fri 3/18/11 MK Electrical Wiring (Connections) 76 days Wed 12/22/10 Wed 4/6/11 Joystick assembly 38 days Mon 2/14/11 Wed 4/6/11 MC Joystick Testing 32 days Tue 2/22/11 Wed 4/6/11 MC Mount Joystick 26 days Wed 3/2/11 Wed 4/6/11 MC Design PCB Board 48 days Mon 1/31/11 Wed 4/6/11 MK Test PCB Board 42 days Tue 2/8/11 Wed 4/6/11 MK Design audio MP3 circuit 76 days Wed 12/22/10 Wed 4/6/11 PA Create volume control for speaker 47 days Tue 2/1/11 Wed 4/6/11 MC Create master on and off switch 38 days Mon 2/14/11 Wed 4/6/11 MK Create on and off switch for audio circuit 70 days Thu 12/30/10 Wed 4/6/11 MK Impliment on board killswitch 46 days Wed 2/2/11 Wed 4/6/11 MC Design remote killswitch 46 days Wed 2/2/11 Wed 4/6/11 MC Final Assembly 24 days Wed 2/9/11 Mon 3/14/11 Mounting of the Tires 3 days Wed 2/9/11 Fri 2/11/11 MK Mount Motor 3 days Wed 2/9/11 Fri 2/11/11 MK Attach Audio Jack 3 days Thu 3/10/11 Mon 3/14/11 MC Mounting of the Seat 3 days Wed 2/9/11 Fri 2/11/11 MC Attach seatbelt 3 days Wed 2/9/11 Fri 2/11/11 PA Attach harness 3 days Wed 2/9/11 Fri 2/11/11 PA Final Testing 1 day? Wed Wed 63

65 11/3/10 11/3/10 Field Testing 40 days Fri 3/4/11 Thu 4/28/11 PA Test seatbelt 40 days Fri 3/4/11 Thu 4/28/11 PA Test Harness 40 days Fri 3/4/11 Thu 4/28/11 PA Test Killswitch 40 days Fri 3/4/11 Thu 4/28/11 MC Test battery charge 40 days Fri 3/4/11 Thu 4/28/11 MC Test Suspension 40 days Fri 3/4/11 Thu 4/28/11 MC Test Audio Jack 40 days Fri 3/4/11 Thu 4/28/11 MK Electrical Safety Testing 40 days Fri 3/4/11 Thu 4/28/11 MK Test Air pressure of Tires 40 days Fri 3/4/11 Thu 4/28/11 MK Test Braking 40 days Fri 3/4/11 Thu 4/28/11 PA Stress Test Power Circuit 40 days Fri 3/4/11 Thu 4/28/11 MK Off-Road Testing 40 days Fri 3/4/11 Thu 4/28/11 MC Test seat removal 40 days Fri 3/4/11 Thu 4/28/11 PA Test for ease of battery accessibility 40 days Fri 3/4/11 Thu 4/28/11 PA Test for engine accessibility 40 days Fri 3/4/11 Thu 4/28/11 PA Check for proper and safe wiring 40 days Fri 3/4/11 Thu 4/28/11 MK Test front lights 40 days Fri 3/4/11 Thu 4/28/11 MK Final Preparation before delivering power chair 44 days Sun 2/27/11 Thu 4/28/11 Clean surfaces 45 days Sun 2/27/11 Thu 4/28/11 PA Wash seat cloth 45 days Sun 2/27/11 Thu 4/28/11 PA 64

66 8. Team Members Contributions to the Project 8.1. Team Member 1: Prince Alam For the frame, Prince was in charge of fabricating and purchasing the footrests, headrest, and arm rests. He made sure that these parts were as light as possible and ergonomic. In addition, these parts will be attached to the power chair, so they can be easily removed if needed. For example, this may be needed for maintenance purposes. In addition, since there are a lot of electrical components on the power chair, the vital components needed to be housed properly. He made a plexiglass box to enclose where most of the power components, such as the batteries and the circuitry, are located. This will ensure that none of the components will malfunction in wet weather. He was in charge of cutting a milling a majority of the pieces of the frame down to the proper size. Also, he fabricated the motor mounts. He drilled most of the holes on the frame to allow for attaching parts. He also fabricated the pockets and holes for bearing placement in the lever arms. He also fabricated the spring mounts. Lastly, he devised a way to attach the safety harness to the power chair. For the mechanical components, he was in charge of finding a proper gear ratio for the motors. This was done to make sure that the motors were giving power to the four wheels in the best manner possible. Lastly, he will install the gears into the power chair. For the electrical components, Prince will be in charge of creating the audio circuit. This circuit will be soldered and attached to the woofer speaker Team Member 2: Marcus Chapman Marcus managed the upper frame work for the power wheel chair, including the seat mounting, joystick placement, and head rest mount. Although, a chair was already purchased, adjustments and changes were needed to be made to make it suitable for the client s needs. In terms of the electrical components of the power wheel chair, Marcus will handle the joystick control and some of the PCB design. He was also accountable for the upper framework model of the power wheel chair using Solid works. He was responsible for the killswitch element. In addition, he helped team members accomplish mechanical and electrical tasks Team Member 3: Mathew Kozachek Matthew was in charge of the fabricating and placing the lever arm mounts. He was also in charge of designing and creating the upper spring mounts. He also designed and fabricated the wheel axles and lever arm axles. He ensured that the wheels and chain sprocket would fit onto the axle and the bearings of the lever arms. Matthew was primarily responsible for designing the power electronics of the wheelchair, including supply, distribution, heat management, and PCB. He designed the Hall Effect Sensor circuits and I/O. Matthew also developed the software for the Arduino microcontroller, which included feedback response from the hall effect sensors and control input from the joystick. 65

67 9. Conclusion Nathan Lamb would like to have more mobility, despite his medical challenges that he faces. Nathan currently struggles with standing on his two feet and having the assistance of his parents to move him around at times. The power wheel chair will give Nathan the freedom to explore around not only his home but at the beach without much support. Power wheel chairs, such as the one being designed for Nathan, normally would cost upwards to around $15,000, which does not include all-wheel drive; however, the budget for the power wheel chair design is a little over $2,000. The power chair that the team designed is a very unique design, and it has some features found in very high end power chairs. It has four-wheel drive. The use of lever arms with individual suspension at four wheels provide enhanced all-terrain capabilities. The team has made sure that the shock was as close to a 90º as possible to make sure the shocks are dampening as many bumps as possible. Most power chairs fail to have this optimum degree angle for the springs. In addition, each wheel is powered by its own DC motor to ensure that the power chair will be powerful enough. As an aside, the motors that are used typically power sitting scooters, which usually have only two motors and are much heavier than the power chair that the team will design. Also, the majority of the frame is constructed out of aluminum to ensure a light-weight design that will have a low center of gravity to limit the possibility of the power chair from tipping over. The electrical components were carefully selected and programmed accordingly. The vital components were encased in a waterproof plexiglass housing to make sure short circuits do not occur. In total, many aspects of the power chair were thought about to make sure that the final product was designed exactly as planned. Overall, the all-terrain power chair will give Nathan the independence to safely travel around his the trails near his home. The power chair will be able to handle the rocks, inclines, and dirt that Nathan may face in the yard. The power chair will be able to handle the terrain because of the four-wheel independent suspension, which is similar to what many off road vehicles have. The chair will also have the ability to be used at the beach on those sunny days. Nathan does not have currently own a power chair. The wheel chair that he currently uses requires Nathan to move himself or have the assistance of his parents. This new power chair will make it easy for Nathan to enjoy himself without much assistance from his parents. The chair can be removed by a latching system if maintenance or extensive cleaning is needed. This will also make transporting the chair easier. The new chair will implement safety features such as a safety harness and headrest, as well as other items including a remote kill switch. The safety harness will keep Nathan stable and help maintain his upright posture in the seat. The kill switch can be used in case of emergency if the device where to move about uncontrollably. The wheel chair will be portable enough so that it can be safely transported in the family minivan. The use of DOT clips will be providing extra security. This device will be personally customized to fit the specific needs for Nathan giving him the best possible experience, while including all the necessary implementations needed for Nathan to have a safe and enjoyable outdoor experience. The audio circuit will allow Nathan to listen to music on his IPod. Nathan will then have a better sense of independence without the constant assistance of his parents. This power wheel chair will help open a new mind set for Nathan, allowing him to go as he pleases. 66

68 10. References [1] Mann, Alex, et al. "Low Center of Gravity All-Terrain Power Chair." UConn BME. N.p., n.d. Web. 20 Oct < Team2/index.htm>. [2] "Myelomeningocele." Google Health. American Accreditation HealthCare Commission, n.d. Web. 6 Sept < [3] "A Properly Aligned Torso Positioned Over A Properly Aligned Pelvis."StandingDani. Davis Made Inc., Web. 5 Sept < [4] "X4-Extreme." Mobility. N.p., n.d. Web. 4 Dec < [5] X4 EXTREME WHEELCHAIR." AbleData. N.p., n.d. Web. 10 Dec < abledata.cfm?pageid=113583&top=0&productid=74924&trail=0>. [6] "Jazzy 614." Jazzy Power Chairs. N.p., n.d. Web. 10 Dec < [7] Shriver, J. Allen. "All terrain vehicle for disabled persons." Google Patents. N.p., n.d. Web. 10 Dec < about?id=-v8daaaaebaj&dq=mountain+wheelchair+hammer>. [8] Schaffner, Walter. "Mid-wheel drive power wheelchair." Google Patents. N.p., n.d. Web. 10 Dec < patents?id=nymfaaaaebaj&printsec=claims&zoom=4#v=onepage&q&f=false>. 67

69 11. Acknowledgements Dr. J. D. Enderle Guidance and funding Serge D. and Pete G. Machine ship Provided mechanical fabrication tips and design advice Marek W. Guidance and assistance Joe LaRosa Power electronics N.E.A.T. Marketplace Provided chair and other components Nathan Lamb and family 68

70 12. Appendix Updated Specifications Physical: Material Type: Aluminum 2 x 2 x.125 square tube stock (lower frame) Rubber tires Foam cushions Mechanical: ITEM Overall Length (with Tires) Overall Width (with Tires) 48 inches 33 inches Overall Height (with Tires) 50 inches Overall Length (without Tires & Seat) 33 inches Overall Width (without Tires & Seat) 25 inches Overall Height (without Tires & Seat)) 18.5 inches Seat Dimensions (L X W X H) 20.5 inches X 20 inches X 29.5 inches Battery Capacity Suggested Max User Weight Maximum Speed 15 Amp Hours Around 100 lbs About 5 mph (Walking speed) Electrical: Motor: 4 24V DC motors Audio Circuit Max Input Voltage: 36 V (3 12V Lithium ion batteries) Battery Life: 3-6 Hours Environmental: Storage Temperature: C Operating Temperature: -18 C to 38 C Operating Environment: Indoors, outdoors, dust, humidity/moisture, dirt, sand Software: PIC Microcontroller for wheelchair control Joystick Control Kill Switch Safety: Restraints: Five-point harness 69

71 DoT-certified clips for transport Feet support Simple headrest Battery: Voltage: Capacity: Dimensions: Weight: Charging Voltage: Rated Discharging Amperage: Max Continuous Discharging Amperage: Maximum Discharging Current: Discharging Cut-off Protection: Lifecycle of the whole pack: Charger: 36 Volts 15 Amp Hours 8.9 x 4.1 x 5.9 inches (225 x 105 x 150 mm) 12.3 lbs (5.6 kg) Volts 15 Amps 30 Amps 60 Amps 40 Amps > 85% capacity after 1000 cycles 2.5 Amp Maintenance: Recharging of battery Seat adjustment for tight fit Cleaning Purchase Requisitions and Price Quotes 70

72 PURCHASE ORDER REQUISITION - UCONN BME SENIOR DESIGN LAB Instructions: Students are to fill out boxed areas with white background Each Vendor will require a different purchase requisition Date: November 5, 2010 Team # 10 Student Name: Prince A, Marcus C, and Matt K. Total Expenses 0 Ship to: University of Connecticut Lab Admin only: Biomedical Engineering FRS # U-2247, 260 Glenbrook Road Student Initial Budget Storrs, CT Student Current Budget Attn: Prince A, Marcus C, and Matt K. Project Sponsor Project Name: All-Terrain Power Chair ONLY ONE COMPANY PER REQUISITION Catalog # Description Unit QTY Unit Price Amount sku: DEV Arduino microntroller 1 1 $50.00 $50.00 Comments Price Quote Shipping TBD File Name: Total: $50.00 Yes or No Vendor Accepts Purchase Orders? Vendor: Address: Phone: Contact Name: SparkFun Electronics No - Order Online Only Authorization: 71

73 PURCHASE ORDER REQUISITION - UCONN BME SENIOR DESIGN LAB Instructions: Students are to fill out boxed areas with white background Each Vendor will require a different purchase requisition Date: November 5, 2010 Team # 10 Student Name: Prince A, Marcus C, and Matt K. Total Expenses 0 Ship to: University of Connecticut Lab Admin only: Biomedical Engineering FRS # U-2247, 260 Glenbrook Road Student Initial Budget Storrs, CT Student Current Budget Attn: Prince A, Marcus C, and Matt K. Project Sponsor Project Name: All-Terrain Power Chair ONLY ONE COMPANY PER REQUISITION Catalog # Description Unit QTY Unit Price Amount Dayton RS " Reference Full-Range Driver 4 Ohm 1 1 $26.71 $26.71 Comments Price Quote Shipping TBD File Name: Total: $26.71 Yes or No Vendor Accepts Purchase Orders? Vendor: Address: Authorization: Phone: Contact Name: 72

74 PURCHASE ORDER REQUISITION - UCONN BME SENIOR DESIGN LAB Instructions: Students are to fill out boxed areas with white background Each Vendor will require a different purchase requisition Date: November 5, 2010 Team # 10 Student Name: Prince A, Marcus C, and Matt K. Total Expenses 0 Ship to: University of Connecticut Lab Admin only: Biomedical Engineering FRS # U-2247, 260 Glenbrook Road Student Initial Budget Storrs, CT Student Current Budget Attn: Prince A, Marcus C, and Matt K. Project Sponsor Project Name: All-Terrain Power Chair ONLY ONE COMPANY PER REQUISITION Catalog # Description Unit QTY Unit Price Amount HEATSINK PWR DUAL BLACK TO $4.07 $8.14 AH173-WL-ADICT-ND IC LATCH HALL EFFECT 3-SIP 1 6 $1.46 $ ND JOYSTICK 5000 POTENTIOMETER 1 1 $69.94 $69.94 Comments Price Quote Shipping File Name: Total: $86.84 Yes or No Vendor Accepts Purchase Orders? Vendor: Address: Authorization: Phone: Contact Name: 73

75 PURCHASE ORDER REQUISITION - UCONN BME SENIOR DESIGN LAB Instructions: Students are to fill out boxed areas with white background Each Vendor will require a different purchase requisition Date: November 5, 2010 Team # 10 Student Name: Prince A, Marcus C, and Matt K. Total Expenses 0 Ship to: University of Connecticut Lab Admin only: Biomedical Engineering FRS # U-2247, 260 Glenbrook Road Student Initial Budget Storrs, CT Student Current Budget Attn: Prince A, Marcus C, and Matt K. Project Sponsor Project Name: All-Terrain Power Chair ONLY ONE COMPANY PER REQUISITION Catalog # Description Unit QTY Unit Price Amount RB-Spa-399 Audio Amplifier Kit (STA540) 1 1 $29.95 $29.95 Comments Price Quote Shipping File Name: Total: $29.95 Yes or No Vendor Accepts Purchase Orders? Vendor: Address: Authorization: Phone: Contact Name: 74

76 PURCHASE ORDER REQUISITION - UCONN BME SENIOR DESIGN LAB Instructions: Students are to fill out boxed areas with white background Each Vendor will require a different purchase requisition Date: December 3, 2010 Team # 10 Student Name: Prince A, Marcus C, and Matt K. Total Expenses $ shipping + tax Ship to: University of Connecticut Lab Admin only: Biomedical Engineering FRS # U-2247, 260 Glenbrook Road Student Initial Budget Storrs, CT Student Current Budget Attn: Prince A, Marcus C, and Matt K. Project Sponsor Project Name: All-Terrain Power Chair ONLY ONE COMPANY PER REQUISITION Catalog # Description Unit QTY Unit Price Amount Replacement wheelchair seat 1 1 $25.00 $25.00 Comments Dan setup an account (UConn BME Team 10) for our team at NEAT, so please just pay for that. We have the seat in our possession. Price Quote $25.00 Shipping File Name: Total: $25.00 Yes or No Vendor Accepts Purchase Orders? Vendor: Address: NEAT Center at Oak Hill 120 Holocomb St. Hartford, CT Authorization: Phone: Contact Name: Spoke with Don. Met and purchased from Dan. 75

77 PURCHASE ORDER REQUISITION - UCONN BME SENIOR DESIGN LAB Instructions: Students are to fill out boxed areas with white background Each Vendor will require a different purchase requisition Date: December 20, 2010 Team # 10 Student Name: Prince A, Marcus C, and Matt K. Total Expenses $ shipping + tax Ship to: University of Connecticut Lab Admin only: Biomedical Engineering FRS # U-2247, 260 Glenbrook Road Student Initial Budget Storrs, CT Student Current Budget Attn: Prince A, Marcus C, and Matt K. Project Sponsor Project Name: All-Terrain Power Chair ONLY ONE COMPANY PER REQUISITION Catalog # Description Unit QTY Unit Price Amount Aluminum 6061-T6 1 3 $35.97 $ Extruded Square Tube 2" x 0.125" Cut to: 96" Cut fee 1 1 $1.50 $1.50 Extruded Square Tube 2" x 0.125" Cut to: 48" Aluminum 6061-T6511 Bare 1 1 $8.46 $8.46 Extruded Rectangle 0.5" x 1.5" Cut to: 24" 10% Discount for ordering over $ ($11.65) ($11.65) Comments Check to have free Mill Test Reports (MTRs) sent to prince@engr.uconn.edu Price Quote Shipping $21.93 File Name: Total: $ Yes or No Vendor Accepts Purchase Orders? Vendor: Address: Authorization: Phone: Contact Name: 76

78 PURCHASE ORDER REQUISITION - UCONN BME SENIOR DESIGN LAB Instructions: Students are to fill out boxed areas with white background Each Vendor will require a different purchase requisition Date: January 21, 2011 Team # 10 Student Name: Prince A, Marcus C, and Matt K. Total Expenses $ shipping + tax Ship to: University of Connecticut Lab Admin only: Biomedical Engineering FRS # U-2247, 260 Glenbrook Road Student Initial Budget Storrs, CT Student Current Budget Attn: Prince A, Marcus C, and Matt K. Project Sponsor Project Name: All-Terrain Power Chair ONLY ONE COMPANY PER REQUISITION Catalog # Description Unit QTY Unit Price Amount 24V 100 Watt Electric Scooter Motor 1 4 $39.95 $ " x 0.125" Cut to: 96" Cut fee 1 Extruded Square Tube 2" x 0.125" Cut to: 48" Aluminum 6061-T6511 Bare 1 Extruded Rectangle 0.5" x 1.5" Cut to: 24" Comments The motor is the third one down from the top of the website Price Quote Shipping $18.08 File Name: Total: $ Yes or No Vendor Accepts Purchase Orders? Vendor: Address: Authorization: Phone: Contact Name: 77

79 PURCHASE ORDER REQUISITION - UCONN BME SENIOR DESIGN LAB Instructions: Students are to fill out boxed areas with white background Each Vendor will require a different purchase requisition Date: January 21, 2011 Team # 10 Student Name: Prince A, Marcus C, and Matt K. Total Expenses $ shipping + tax Ship to: University of Connecticut Lab Admin only: Biomedical Engineering FRS # U-2247, 260 Glenbrook Road Student Initial Budget Storrs, CT Student Current Budget Attn: Prince A, Marcus C, and Matt K. Project Sponsor Project Name: All-Terrain Power Chair ONLY ONE COMPANY PER REQUISITION Catalog # Description Unit QTY Unit Price Amount 36V 15AH v2.5 LiFePO4 Battery Pack w/ 2.5A charger 1 1 $ $ " x 0.125" Cut to: 96" Extruded Square Tube 2" x 0.125" Cut to: 48" Comments Price Quote Shipping $85.00 File Name: Total: $ Yes or No Vendor Accepts Purchase Orders? Vendor: Address: Authorization: Phone: Contact Name: 78