All-Terrain Power Chair Redesign. All-Terrain Wheelchair Redesign. Beach Wheelchair

Transcription

1 Final Report All-Terrain Power Chair Redesign Project 1 for Annalee Hughes All-Terrain Wheelchair Redesign Project 2 for Nathan Lamb Beach Wheelchair Project 23.1 for Danielle Giroux Team 1 Stephen Elovetsky, Steven Rogers Client Contact: Susan Lucek 777 Tolland Stage Road Tolland, CT (Home) (Mobile) (Office) slucek@nerac.com Janice M. Lamb 142 Barnes Road Stonington, CT (Home) (Mobile) (Office/Fax) janice.lamb@linde.com David & Suzanne Giroux 53 Charlotte Drive Tolland, CT (Home) (Mobile) girouxs@sbcglobal.net

2 Table of Contents Abstract. 2 1 Introduction Background Annalee Nathan Danielle Purpose of the Projects Annalee Nathan Danielle Previous Work Products Patent Search Results Map of the Rest of the Report 7 2 Product Design Introduction Alternative Designs Annalee Nathan Danielle Optimal Design Objective Annalee Nathan Danielle Subunits Annalee Nathan Danielle Prototype Annalee Nathan Danielle Realistic Constraints Safety Issues 32 5 Impact of Engineering Solutions Life Long Learning Budget Team Members Contributions to the Projects Stephen Elovetsky Steven Rogers Conclusion References Acknowledgments Appendix 39 1

3 Abstract All-terrain and beach wheelchairs are becoming more popular and more common, however, they are still too expensive for many people and families to purchase. Annalee Hughes and Nathan Lamb are both very adventurous children who would benefit greatly from all-terrain power chairs, and Danielle Giroux is a very social young girl that would benefit from an easy to maneuver beach wheelchair. Over the course of the year, our team is working on modifying allterrain power chairs that were built for Annalee and Nathan by previous senior design teams. We are also working on designing and building a beach wheelchair for Danielle that is a modification of an old, collapsible stroller that she had when she was younger. The all-terrain power chair that is being redesigned for Annalee features an automated self-leveling system for the seat of the chair. Controlled by a microcontroller, the system reads tilt data from accelerometers placed on the chassis of the chair and on the seat and controls a linear actuator mounted beneath the seat. The actuator tilts the seat back when the chair is traveling downhill and tilts the seat forward when the chair is traveling uphill. The system also sounds a buzzer if the chair is traveling on a slope of an angle greater than 30. With these features, the chair is capable of giving the client freedom of movement on many terrain areas while also keeping her safe. The all-terrain wheelchair that is being redesigned for Nathan features improved steering and handling, and improved joystick. The front suspension of the chair is being replaced with caster style wheels giving it superior turning capabilities over the previous design. The joystick is being replaced with a more robust one that will last the lifetime of the chair and will be mounted to new armrests on the seat that will provide improved comfort of use for the client. The all-terrain wheelchair will give Nathan the freedom of movement that he has not had before, allowing him to enjoy more outdoor activities with his family and friends. The beach wheelchair the is being designed for Danielle features a wide base and easy turning, as well as the ability to collapse and be disassembled partially for easy transportation and storage. The chair will ride on four large polyurethane balloon tires that will allow it to move across the sand easily. The casters are moved from the front of the chair to the back to make pushing and turning the chair much easier. When it comes time to move the chair to or from the beach, it will collapse to a manageable size making it much easier to transport and also to store in the Winter months. The beach chair will provide Danielle and her family a much easier means of moving around on the sand, allowing them to spend more time enjoying their vacations and day trips to the beach. 2

4 1 Introduction 1.1 Background Annalee Annalee is an eleven-year-old girl with cerebral palsy. Cerebral palsy is a condition that usually involves brain and nervous system functions. Cerebral palsy is caused by injuries or abnormalities in the brain and symptoms of the condition vary from individual to individual [1]. In the case of Annalee her cerebral palsy has resulted in underdeveloped muscles in her legs and upper body. The lack of proper stimulation of the muscles by the brain and nervous system has resulted in their being relatively weak and underdeveloped, meaning that Annalee cannot stand up and support her own weight by herself. Annalee is very adventurous and wants to be independent in what she does. She thoroughly enjoys exploring her spacious, three-acre backyard. Her family has a barn, pond, and blueberry bushes that she enjoys visiting and exploring. The problem is that the family s backyard is not flat, but instead very hilly and rocky. Due to her cerebral palsy, Annalee uses a power chair to move around, controlling it via a joystick with her right hand, however it is not capable of safely traversing the terrain in her backyard. Previously, she has tipped over her power chair while trying to use it in the backyard and because she is not very strong, she cannot right the chair or herself when this happens. Two years ago, an all-terrain power chair was built for Annalee by a group in Senior Design. The chair was designed to auto-level the seat so that Annalee could use it to safely traverse her family s property. When Annalee first received the chair, it worked as expected. After a month or two, however, it began to malfunction and the auto-leveling system stopped working all together. The brakes on the chair were also not working properly, resulting in a very long stopping distance. Our goal is to remedy both of these issues so that Annalee can use the chair to safely explore her backyard Nathan Nathan is a twelve-year-old boy with myelomeningocele and an autism spectrum disorder. Myelomeningocele is a form of spina bifida. Myelomeningocele is a birth defect in which the spinal canal and backbone do not fuse properly [2]. In Nathan s case, the myelomeningocele caused partial paralysis of the legs, thus resulting in weakness in the muscles in his hips, legs, and feet. The myelomeningocele also caused hydrocephalus, which is a buildup of fluid in the brain. Nathan underwent surgery to drain the fluid built up in the brain into his bladder, where it could be excreted by the body naturally. Nathan also has weak trunk strength, which results in an abnormal, slanted sitting posture. As mentioned by his parents, this may be causing Nathan to develop scoliosis. Along with his physical disabilities, Nathan has an autism spectrum disorder. Autism is a developmental disability that causes problems or difficulties in social interaction and communication. Autism is called a spectrum disorder because it is a group of disorders with similar symptoms and symptoms can range from mild to severe [3]. Like any child his age, Nathan enjoys participating in outdoor activities with his family and friends. Due to his myelomeningocele, Nathan relies on a manual wheelchair, pushed by someone else, to move around. His family is in the process of trying to get a power chair for him to use around their home and at his school. Nathan is unable to move around and interact with people and his surroundings as independently as he could. 3

5 Last year, a Senior Design team designed and built an all-terrain wheelchair that would allow Nathan to traverse the terrain around his house and other outdoor areas freely and independently. Nathan is proficient with his right hand, therefore the chair is controlled with a joystick mounted on the right side of the chair. When the chair was given to Nathan, it did not work properly. The movement of the chair did not correspond to the direction that the joystick was moved in. Along with that, when the chair turned it would jump and jitter until it stopped moving. Both of the factors made it very unsafe for Nathan to use. Our goal is to determine the cause of the problems and redesign parts of the chair in order to make it safe for Nathan to use Danielle Danielle is an eleven-year-old girl with cerebral palsy. Similarly to Annalee, Danielle s cerebral palsy has caused her lower body, especially her leg muscles, to become underdeveloped and unable to support her standing and walking. Danielle is very friendly and social. She loves spending time with her family and friends and really enjoys trips and vacations to the beach. Danielle currently uses a power chair to move around her home and school. The chair, however, is not designed to travel on uneven, off-road terrain. This means that when the family goes to the beach or other outdoor activities, Danielle usually cannot use her power chair and thus relies on others to mover her around in a manual one. Her family rents or borrows beach wheelchairs when they visit beaches, but these chairs are difficult to move and the rental fees add up, making it more difficult to go to the beach as often as they may like. Our goal is to design and build a collapsible and easy to maneuver wheel chair that will make the family s trips to the beach less difficult and more enjoyable for everyone. 1.2 Purpose of the Projects Annalee The goal of the project for Annalee is to fix the low center of gravity power chair that was built for her two years ago. It was originally designed with an auto tilt correction mechanism built into the seat of the chair. It was supposed to keep Annalee level, giving the chair more balance as it traversed the hills and rocks in her family s yard. This anti-tilt mechanism and the braking system of the power chair are not working correctly, making the chair unsafe for Annalee to use on her own. The team needs to analyze the mechanical and electrical systems of the power chair to determine what is causing the malfunction and correct any issues that are found Nathan The goal of the project for Nathan is to fix the all-terrain power chair that was built for him last year. It was designed to allow Nathan to traverse his yard, the beach, and other rough terrain on his own. It was built with four-wheel drive to make it more efficient and capable of traversing the varying terrain types that he would encounter. When the chair was completed, there was little time to test all of the mechanisms of the chair and when Nathan tried to first use it, his parents noticed that the chair did not respond properly to the movement of the joystick. Nathan was unable to use the chair after that because it was not safe for him to operate on his own. The joystick was also very small and not very strong. Nathan s parents said that Nathan has a tendency to be more forceful with things because he doesn t understand that he is damaging them. They asked that the joystick be upgraded to one that was more robust and would withstand the more aggressive treatment that Nathan would give it. The team needs to analyze the electrical 4

6 systems and programming to determine what is causing the power chair to malfunction and make the appropriate changes to make it safe for Nathan to use. In doing this, the joystick will be replaced with a new, more robust, joystick that will last the lifetime of the chair. The seat of the chair also has to be modified slightly to better accommodate Nathan s growth and to provide the most comfortable environment for him to use his chair in Danielle The goal of the project for Danielle is to make her movement easier on the uneven terrain at the beach. The beach wheelchair that we will build is going to be designed to allow Danielle s parents to easily move Danielle over the sand when they go to the beach. Traditional manual wheelchairs have very thin wheels that do not move across the sand, but rather cut into it, making them impossible to use at the beach. The beach wheelchairs that the family usually rent when they go to the beach are also not easy to move through the sand. The wheelchair that we design will move across the sand with the least amount of effort possible, allowing Danielle and her family to spend more time enjoying the beach and less time trying to get there. 1.3 Previous Work Products All-terrain power chairs are becoming more popular, however, they are generally very expensive. PlanetMobility.com features a number of all-terrain power chairs with a range of features. One such power chair is their Viking 4x4, which features four-wheel drive and a selfleveling seating system. The Viking 4x4 is capable of traversing sand, mud, snow, and other rough terrain with ease. The gyroscopic self-leveling seating system allows the power chair to climb hills, ramps, and stairs at an angle of up to 36. Another all-terrain power chair featured on PlanetMobility.com is the X5-Frontier. The X5-Frontier is a mid-wheel drive all-terrain power chair. Unlike the four-wheel drive power chairs, the mid-wheel drive chair drives off of only two wheels at the center of the length of the chair and has four smaller support wheels at each corner. This setup is less stable in general making it inadequate for off-road use, though the X5-Frontier claims to be comparable to the 4x4 chairs on most terrain. While both of these power chairs are very powerful and capable of handling all types of terrain, they come with a hefty price tag. Both the Viking 4x4 and X5-Frontier have base prices of nearly $10,000. With many of the available options, the price of either chair could easily increase by hundreds or thousands of dollars, making them even more expensive for the family to purchase. 5

7 Figure 1: Three Viking 4x4 all-terrain power chairs demonstrating the power chairs ability to climb steep inclines while keeping the rider level. Figure 2: The X5-Frontier all-terrain power chair with mid-wheel drive. Beach wheelchairs are also becoming very popular and in demand. Persons that need a wheelchair to move around used to never be able to go to the beach because it is near impossible to push a standard wheelchair across the sand. Beach wheelchairs use polyurethane or PVC wheels to easily traverse even the softest sand. They allow disabled people and their families to enjoy the beach without having to worry about how to get there. Figure 3: A De-Bug beach wheelchair from Deming Designs, Inc. 6

8 1.3.2 Patent Search Results In 1998, Adolph Hammer filed a patent for a self-propelled all-terrain vehicle designed for paraplegics. It used two track mechanisms in place of wheels and was powered by an internal combustion engine. The seat of the vehicle moved horizontal towards the front of the vehicle to decrease the distance needed for a person to move between their wheelchair and the powered vehicle. In 1995, Micheal Deming filed a patent for an all-terrain wheelchair. It had large, wide wheels that allowed for easy maneuvering over sand and other similar terrain. The rear wheels swivel and pivot to allow for easy turning and greater stability over uneven terrain, which is common on beaches. 1.4 Map of the Rest of the Report Throughout the rest of this report, we will go into more detail about the process by which we designed each project. We will give a more detailed objective for each of the projects as well as a list of the subunits of each project as we originally planned to implement them, and a detailed description of the final prototype. Following that we will discuss some of the constraints that we are working with and any safety issues that are taken into consideration for each of the projects individually as well as a whole. The impact of the solutions on the engineering community and new skills that we have learned throughout the process will be discussed, followed by an updated budget and timeline for the projects. The contributions of each team member will be discussed, followed by a brief conclusion. 2 Project Design 2.1 Introduction In the following sections, we will describe the planning and brainstorming that went into picking our optimal design for each project. For Annalee and Nathan s projects, we were modifying past projects (Spring 2010, Team 2 & Spring 2011, Team 10, respectively) so that they would function properly and more safely so rather than alternate designs we state the game plan that we are following. For Danielle s chair, we came up with three different alternative designs, each with their own unique features. Following the alternative designs, we go into detail about the individual subunits of the optimal designs for each project. The mechanical, electrical, and software related aspects of each design are outlined and broken down into the individual components that make each chair work Alternative Designs Annalee The power chair that was built for Annalee had a built in, actuator controlled seat tilt. An accelerometer and a microcontroller chip were used to automate the operation of the actuator in order to keep the seat level at all times without the need to manually adjust the actuator. The microprocessor chip and other electrical components were soldered to a generic breadboard. This breadboard will be replaced with a newly designed printed circuit board, or PCB. In designing the PCB, we will be able to test the circuit and any changes we make to it to ensure that it functions the way we need it to. Once it is tested, the board will be printed and used in the chair, making the wiring much neater and more reliable. The microprocessor chip will then have to be 7

9 reprogramed in order to compensate for any changes in the circuitry and to ensure that the seat can auto-level itself. The accelerometer senses the change in tilt and outputs a voltage that is related to the tilt. Based on this relationship, the microcontroller will know exactly how much tilt the chair is experiencing. It will then be able to send the appropriate signal to the actuator to correct the tilt of the seat. A switch will also be incorporated to allow the user to turn off the automatic leveling and manually adjust the seat s tilt Nathan The power chair that was built for Nathan was not completed, resulting in the chair not functioning properly. A microcontroller was never implemented in the system but will be now so that the chair can function properly. The microcontroller will be programed to analyze the input from a new joystick, and send the appropriate signals to the motor driver that is on the chair now. All electronic circuitry will be designed and tested using Multisim. PCBs will be created to allow the wiring to be clean and neat, while allowing the circuitry to function more reliably. The kill switch for the electric motors will be mounted in an easily accessible location so that if the chair malfunctions or Nathan loses control of the chair, someone can easily cut power to the motors and stop the chair safely. The joystick will be replaced with a more robust one that will last longer and be able to stand up to more aggressive use from Nathan. The Plexiglas housing that was created for the battery and other electronic components will be rebuilt with more sturdy material so that it will not break Danielle Alternate Design 1 This design for the beach wheelchair is a three-wheeled, low riding chair. The frame will be made out of aluminum round stock to ensure that it is light but also strong. The three wheels will be polyurethane balloon wheels that allow the chair to move easily across the sand. The rear wheels will be larger and the front wheel will be smaller. The seat will be positioned in between the rear wheels, slightly reclined so that Danielle can sit back and have her legs extended along the length of the frame while still being comfortable. The three wheels will be fixed, and the handle bar will be at an angle that allows for the person pushing the chair to easily lift the front tire off the ground and turn the chair when pushing down on the handle bar. 8

10 Figure 4: Solidworks three dimensional layout of the three wheel beach wheelchair. Alternate Design 2 A more traditional looking wheelchair was used as the template for this beach wheelchair design. This chair, like typical wheelchairs, has a seat with a back and armrests that is on a frame consisting of four wheels. The overall chair frame will be made out of hallow aluminum bars to ensure both stability and be lightweight. Two different sizes of polyurethane balloon tires were used in this construction. The rear wheels are smaller than the forward ones because they are each part of a castor that rotates freely on an axle. The advantage of putting rotating tires in the back rather than the traditional front is to allow better ease and maneuverability for the one pushing the chair by the handlebar because torque is being applied further from the point of rotation. All four of these tires must have a wide base in order to move easily across the sand and not sink and get stuck in the process. A headrest has been included for Danielle s comfort and safety as she moves across uneven and bumpy terrain. It is important to point out that the seat must be positioned low to the ground as to have a low center of gravity so that it will not tip as easily going across the uneven sand. 9

11 Figure 5: Solidworks three dimensional layout of the four wheel, modular beach wheelchair design. This beach wheelchair has been designed to disassemble for the purpose of easy storage and transportation to and from the beach. The seat of the chair has four bolts that protrude through the frame and are secured using wing nuts so it can be disassembled without the use of additional tools. The forward tires use the same concept; they are held onto the axle by wing nuts that can be easily removed. The rear wheel castors are also held into place on the frame by bolts and wing nuts. This disassembly will allow easy stacking in a van trunk or storage closet. Alternate Design 3 This wheelchair design is going to be a modification of one of Danielle s existing strollers from when she was younger and doesn t use anymore. The frame and design are sound for this project. Essentially the main things to change on the stroller to make to a functional beach wheelchair are to modify the seat and tires. The seat is obviously too small for Danielle since she has grown, so a new wheelchair seat must be either built or modified from another wheelchair so that she can sit comfortably. As mentioned before, it is important to point out that the seat must be positioned low to the ground as to have a low center of gravity so that it will not tip as easily going across the uneven sand. The wheels on the original stroller are definitely too thin to glide across the sand, so they must be replaced with the much wider polyurethane tires. The front tires will be smaller and in castors, like the original stroller, and the rear wheels will be bigger and fixed to better support the frame. 10

12 Figure 6: Large beach wheelchair wheel. Figure 7: Small beach wheelchair wheel and caster assembly. The main reason for recycling Danielle s old stroller is that it has a collapsible feature making it easy to store and transport. The same wing nut system, as seen in this project s Alternate Design 2, will be used to secure and disassemble the tires from the chair frame. The new seat will probably not be compatible with the collapsible design, so it will have to be removable as well. The overall advantage to this design is the conciseness of the disassembled parts making it easy to transport. The optimal design is based mainly off of the third alternate design for Danielle s project. The design fits best with the required specifications, as it is already collapsible and the frame is relatively lightweight. The largest wheels will be removable in order to make the chair even more portable, easy to lift and store. The design is also very cost efficient because we received the frame for free from the client and it is preassembled, saving time as well. 2.2 Optimal Designs Objective Annalee The chair that was designed and is being modified for Annalee will give her more independence in moving around in her backyard. The power chair has an actuator that controls the tilt of the seat. The tilt can be controlled manually, and an automated control feature is being implemented. An accelerometer on the seat will register the angle at which it is sitting. The accelerometer s output is read by a microcontroller which in turn controls the actuator to automatically level the seat so that Annalee is better able to control and maneuver her chair on the uneven terrain. 11

13 Nathan An all-terrain wheelchair was built for Nathan last year by one of the senior design team. The chair malfunctioned and the four-wheel-drive caused the turning of the chair to be bumpy and unsafe. The front powered wheels are being replaced by caster style wheels so that the chair can turn and maneuver much more safely and easily. The joystick is being replaced with a more robust one that can withstand more aggressive use from Nathan, and the electrical controls will be wired correctly as to avoid any further malfunctions Danielle Danielle s family would like for a wheelchair to be designed that would enable her to move across a sandy beach and into the water, while being lightweight and easy to transport and store. Thus, the basic frame of this wheelchair will be an old cruiser stroller that Danielle used to use when she was younger. The size of the frame is adequate for her size now and the overall design of the beach wheelchair. It has a built in feature of the frame back and handlebar collapsing and folding in on the chair bottom, creating an easily stored and transportable wheelchair. Additions will need to be made to the chair in order to make it beach-worthy. Instead of conventional wheelchair tires that are relatively thin and would sink into the sand as they moved across the beach, the tires on the beach wheelchair will be balloon tires made of polyurethane. Two of these tires will be larger and fixed on the front of the wheelchair, while two slightly smaller tires will be mounted in casters on the back and will be able to freely and independently rotate. A new chair will need to be created and mounted in order to fit Danielle now and as she grows into the chair Subunits Annalee Mechanical Actuator The actuator is positioned under the seat of the power chair and controls the tilt of seat with respect to the base of the chair. An electrical signal from the actuator control unit results in movement of the piston in the actuator. The actuator control unit, in turn, receives input from either the manual tilt control buttons, or from the automated tilt sensor, depending on which mode is selected by the occupant. When the piston moves, it creates a torque at the hinge that is located at the rear of the seat. Based on the direction of the piston s movement, it will tilt the seat backwards or forwards. The tilt of the seat is used on hills to prevent Annalee from falling forwards out of the chair when she is travelling downhill, and to give her better visibility and control when she is going uphill by keeping her level. Electrical Batteries Two 12 V, 75 Ah, Deep Cycle batteries provide all the power necessary for the power chair to operate. The batteries are wired together in parallel, providing a total of 24 V of power to the components on the chair. 75 Ah is the equivalent of the batteries being able to supply a steady current of 75 Amps for one hour. None of the components on the power chair draw that 12

14 much current, but the higher Amp-hour capability of the batteries will ensure extended use periods for the chair. Deep Cycle batteries are built to be discharged anywhere from 50 to 80% before they have to be charged again. This allows for long usage periods necessary to operate a power chair, before the batteries need charging [4]. Charger A 3-stage charger is used to charge the two main 12 V batteries. A 3-stage charger is used because it helps lengthen the life of the batteries by preventing them from being overcharged if left charging for too long. The charging unit charges the batteries quickly with a high current rate until the battery voltages rise to about 80 to 90%. At this point, the current is reduced, and the charger outputs the maximum voltage of the batteries. This ensures that the batteries will charge fully without being damaged by excessive amounts of current. Finally, the charger reaches stage three of the charging, commonly called trickle charging, which is used to prevent the fully charged battery from discharging [4]. Accelerometer The accelerometer will act as a tilt sensor to allow the seat to automatically level itself. The accelerometer being used is an ADXL335 from Analog Devices. It is a tri-axis accelerometer that can measure the static acceleration of gravity for use in tilt sensing applications such as this. The accelerometer runs off of a single supply voltage between 1.8 and 3.6 V, and outputs a conditioned voltage for each of the three sensing directions [5]. The output of the appropriate direction will be wired to the input of the microcontroller that will be described later, which will then control the actuator s movement to level the seat when it travels up or down a slope. Figure 8: ADXL335 accelerometer that will be used as a tilt sensor on Annalee s power chair. Software Microcontroller A PIC16F874 microcontroller will be the heart of the automatic leveling seat. The microcontroller is programmed using C. The output voltages from the accelerometer will be read by the microcontroller. Based on these values, the microcontroller will send a signal to the 13

15 actuator control unit causing the actuator to extend or retract, changing the tilt of the seat so that it is level. The operator will be able to decide between automatic and manual control of the seat s tilt. When manual control is used the microcontroller will still operate, it just won t be able to send signals to the actuator control unit. This way, once automatic control is selected, the seat will begin to adjust right away Nathan Mechanical Suspension and Wheels The four-wheel-drive system that was implemented on the chair caused problems with the turning ability of the chair. Because all four drive wheels are fixed, the turning causes the tired to be dragged sideways, resulting in a bumpy and unsafe turn. In order to remedy this, the front suspension and drive wheels will be replaced with free spinning caster style wheels. This will result in the chair being only two-wheel-drive, however, it will be much safer to use and maneuver. When the rear wheels spin in opposite directions or at different speeds to turn the chair, the front wheels will be able to spin and rotate freely without any resistance, allowing the chair to turn without jumping and possibly tearing up the lawn or other surface it is riding on. Overall the chair will be much easier for Nathan to control on any terrain. Figure 9: New caster assembly that will be built for use on Nathan s power chair. Battery and Electronics Housing The battery and electronics housing that was built on the chair was made out of Plexiglas. Due to the size and weight of the battery, the housing did not hold up and has broken and fallen apart. A new housing will be purchased and modified to fit on the chair. This new housing will better support the weight of the battery and will help keep the other electrical components secure and protected from the elements, while allowing easy access to all of it in case the need to replace anything arises. 14

16 Electrical Joystick The joystick that was originally implemented on the chair is rather small and flimsy. Nathan s parents said that Nathan tends to be a little rough with the things he handles because he does not realize that he is causing harm to them. Therefore, the joystick is being replaced with a more robust one that will better withstand the aggressive treatment that Nathan will give it. The new joystick has a metal housing and a stronger joystick shaft that will last longer. The joystick is connected to the chair through a 15-pin D-Sub connector which will allow the joystick to easily be removed if it has to be repaired or replaced in the future. Figure 10: Image of the new joystick to be used on Nathan s power chair. Battery A 12 V, 200 Ah, Deep Cycle battery is used to power the chair s two motors. The Deep Cycle battery and 200 Ah output will allow the power chair to be used for an extended period of time before it has to be recharged. This will prevent the chair from dying after a very short trip to the beach or other family outing. Nathan will be able to use his power chair for the entire length of an outing and then be able to charge it when his family is at home again. Motor Controller A Sabertooth 2x25 motor controller is used to translate the joystick movement into the appropriate directional rotation of the two powered wheels. The motor controller takes power from the battery and feeds it to the correct motors when the joystick is moved. From the battery power, the Sabertooth 2x25 can output 5 V to power the joystick, and can read the two directional output of the joystick based on the voltage values that are returned to inputs S 1 and S 2 on the motor controller. Based on these values, the controller sends voltage signals to motors 1 and 2 so that the chair moves appropriately. 15

17 Figure 11: Sabertooth 2x25 motor controller used to control the movement of Nathan s power chair based on the input of the joystick. Kill Switch The kill switch will be the overall power switch for the chair. When the switch is in the closed position, power will be allowed to travel from the battery to the motor controller so that the joystick will function and the controller will be able to power the motors. When the switch is in the open position, all power to all of the components of the chair will be cut. The switch will be placed at the rear of the chair on the outside of the electronics housing so that it can be easily accessible to anyone that needs to shut the chair off in an emergency. The switch will also help in storing the chair because the Sabertooth will be disconnected from the battery, increasing the length of time that the battery will last before needing to be recharged again Danielle Mechanical Wheelchair Frame The overall frame of this wheelchair will be a recycled stroller that Danielle had used when she was younger. This particular stroller frame has a wider, more square base than most other conventional strollers out on the market, which makes it ideal for supporting the larger tires. The frame consists of hollow tubes made of steel for strength and durability. In the middle of the long bar that makes up the back of the chair, there are two releases that hook the chair into place or make it fold down and collapse onto itself. This is ideal for storage and transporting in a confined trunk or van space. Since different tires will be used with much larger dimensions, the frame by itself cannot support all four tires while staying level with the ground. Additional bars that extend down will have to be added to the front of the chair frame in order for the wheel axle to enter and be level with the back tires in casters that are of a slightly different diameter. 16

18 Figure 12: Image of the original stroller and the Solidworks representation of the modified wheels on the frame. Tires/Casters The tires for this wheelchair are custom made balloon tires that are quite large. They are made of polyurethane and filled with air to make them durable yet lightweight. These special tires are made to be very wide across which makes a very large contact area with the ground. This enables a much greater weight distribution across the tires as they touch the ground. Like with snowshoes, the reasoning for this is making a base with greatly increased surface area makes it so that there is less weight pushing down against the ground at any given point. This allows the wheelchair to practically glide across the sand as it moves. Typical tires and wheelchair wheels would sink into the sand as they move due to the decreased weight distribution that the thin wheels provide. Figure 13: Larger polyurethane balloon wheel and smaller polyurethane balloon wheel in the caster housing. 17

19 The four tires are going to be of two different sizes for the sake of being put in casters and turning. The front two tires will be fixed and attached to the frame extension as to accommodate for the larger size of the wheels. These tires need to be relatively large in order to provide maximum weight distribution so it doesn t sink in the sand. These two tires will be made to come off the frame in order for easier storage and transport, secured to the frame via a wing nut and bolt or a pin. The other two tires will be in casters, which are devices that contain an axle and house the tire from both sides. These casters are attached to the frame of the chair and are able to rotate freely and independently so the chair can turn. These two tires must be smaller to accommodate the casters and be able to fit under the chair. Typically, wheelchairs are seen with the casters on the front so they turn like a car or shopping cart. The casters instead are placed in the back. The uneven and changing terrain of a sandy beach makes it inherently hard to turn a wheelchair. The casters are placed nearest to the handlebar so that a lesser amount of torque is needed to turn the chair, making it easy to overcome the difficulties of moving across such uneven terrain. Seat The old seat in the stroller is too small for Danielle to fit into comfortably. It must be taken out and replaced with one that she will fit into. It must also be considered that the seat may get wet from the seawater. The seat cushion will be a conventional wheelchair seat, but it will have to also be wrapped in a waterproof sleeve to prevent it from being ruined by the saltwater. The seat back will be made out of a mesh fabric that is porous and easy to dry if wet. The seat bottom will be supported by a base addition made to the wheelchair frame, while the backing will be incorporated into the existing back poles. 2.3 Prototype 2.4 Annalee The final prototype design for Annalee s chair uses two accelerometers to acquire angle measurements from both the frame and the seat. Because the seat can only lean backwards, the accelerometer on the frame is used for comparison purposes to ensure that the seat is not lowered too far as to damage the actuator or other parts of the chair in any way. The frame mounted accelerometer is packaged in self-adhesive heat shrink. The accelerometer was wired up and placed into the heat shrink tube. It was heated and the ends were pressed together to seal off the board in order to insulate it from excessive moisture. Images showing the location of the accelerometers on the chair can be seen on the next page. 18

20 Figure 14: Image showing the PCB with one of the accelerometers, all of which is mounted to the seat of the chair. Figure 15: Image showing the second accelerometer mounted to the frame of the chair. 19

21 Figure 16: 3D image (left) and schematic view (right) of the PCB that was designed for the auto-leveling circuit. The heart of the auto-leveling system is a PIC microcontroller. It is mounted to a printed circuit board (PCB) that was designed to hold it and all of the other necessary electrical components. The primary components on the board are the PIC, accelerometer, and three relays. The board is powered by two 9 V batteries, in parallel. The batteries feed one 5 V regulator and one 3.3 V regulator. The 5 V is used to power the PIC alone, while the 3.3 V is used for the two accelerometers and the alarm buzzer. The pic controls the actuator via two of the three relays. The third relay is used to control the buzzer. Based on the accelerometer inputs, the microcontroller sends power to one of the actuator relays, causing it to extend or contract, thus moving the seat closer to level. If the chair is on a slope that is greater than a 30 incline or decline, the buzzer will go off alerting the user to use extreme caution and to avoid that slope if possible. The electronics box containing the PCB, batteries, and buzzer, is mounted on the side of the seat, as seen in Figure 15. The box has two toggle switches and a dual push button switch mounted on it. The right hand toggle switch turns the entire circuit on and off. The left hand toggle switch enables and disables the automatic control of the actuator. The dual push button switch allows for manual control of the actuator, given that the batteries in the box die or there is a need to override the automatic actuation. When the auto actuation switch is disabled, the PIC is still powered and can still set off the buzzer if the user travels on a slope that is too steep. Aside from the auto leveling system, the chair is controlled by the model s standard joystick. The power switch and speed knob are mounted on the rear of the joystick module and the stick itself is used to maneuver the chair. The chair is powered by two 12 V deep cycle batteries that are housed in the base of the chair. The finished chair can be seen in Figure

22 Figure 17: Image of Annalee s finished power chair. 2.5 Nathan The final prototype design for Nathan s chair uses the original aluminum frame with a number of modifications. The original design featured four fixed drive wheels. The idea behind it was solid, allow the chair to move in a manner similar to a tank or other track mounted vehicle. The issue was that the chair did not have tracks, it had rubber tires, which are not made to move sideways when turning the way tank tracks work. This resulted in very bouncy turns that would damage lawns or other surfaces that the chair was driven on. In order to fix this problem, the front motorized wheels were replaced by free moving casters that were custom built. The casters allow the chair to move freely and maneuver on any surface, making it much safer for the user. 21

23 Figure 18: Front casters of Nathan s power chair. Another part of the chair that was causing handling issues was the joystick. The original design used a small, flimsy joystick and the solder connections were loose and broke free making the chair very unpredictable. This was resolved by replacing the old joystick with a more robust power chair joystick. This joystick is connected to the motor controller via a 15-pin D-sub connector. Since the connector is standard to the joystick, there is a much lower chance of solder joints breaking off and causing the chair to lose control. The pins of the joystick were mapped and the necessary wires were carefully soldered to the pins of a female D-sub connector in order to create a simple and secure connection between the joystick and motor controller. This connection also allows for the joystick to be removable, should there be the need to replace or fix it. The motor controller is the heart of this chair s electronics. It is a Sabertooth 2x25 motor controller that takes input from the joystick and directly translates it to control the two rear motors. The motor controller is powered directly from the 12 V deep cycle battery of the chair, which it uses to power both the motors and the joystick. A built-in 5 V regulator allows the motor controller to feed a constant 5 V to the joystick so that it has consistent readings from its two returns. One return is the forward to back position of the joystick, and the second is the side to side position of the joystick. With these readings, the controller sends signal(s) to one or both of the motors so that the chair moves in the direction the user indicates with the joystick. The armrests were previously mounted to the frame of the chair, making them parallel to the ground. The seat, however, is tilted back slightly, making the armrests uncomfortable. Thus, the armrests were moved and are now mounted directly to the frame of the seat. This way, they are parallel to the base of the seat, making them more comfortable for the operator to use. The armrests are height adjustable and the joystick on the left armrest can be extended or contracted from the armrest for the user to be most comfortable. 22

24 Figure 19: Seat, armrests, and joystick mounted on Nathan s chair. The original battery housing was replaced with two battery boxes, one for the deep cycle battery that powers the chair, and one to house the motor controller. The box that houses the battery is mounted on top of the frame at the back of the chair, and the motor controller box is suspended beneath that box. The battery is one of the heaviest components of the chair, therefore it needs to be supported by the frame, and the motor controller is extremely light and does not require much support, making the location for both ideal. Figure 20: Battery boxes on Nathan s chair. 23

25 Finally, the seat is mounted to the frame at three locations. The front of the chair attaches to a bar that runs across the front of the frame, and the back corners of the seat attach to mounting stubs on either side of the frame. The rear mounts are secured using a nut and bolt on each side, and the front attachment is a latch system that is built into the seat frame. The armrests are removable, as is the seat itself, making for easy disassembly for transportation or storage in a small space. Figure 21: Image of Nathan s finished power chair. 24

26 2.6 Danielle The final prototype design of this beach wheelchair is mainly based off of Danielle s old stroller frame. This frame was ideal to use because of its built in collapsible design which makes transporting it too and from the beach incredibly easy. The front of the stroller frame had to have additional aluminum metal stock in order to accommodate the large balloon tires without interfering with chair function. Original portions of the old stroller frame were sawed off to start this process. From here, 90 o elbow clamp connectors, an aluminum plate, and hollow square tubing were welded to the chair frame. At the end of the square tubes, a 1 diameter hole was cut so that a 34 solid rod of the same diameter could fit through, be welded in place, and serve as the axle rod for the two front wheels. This rod also has spacers on each end welded in place to keep the wheels in place. Pin holes were also drilled at the ends of the rod, where circular pins would be used to keep the front tires at a fixed point on the rod. The entire metal frame was the disassembled and shipped off to Central Connecticut Coatings so that a turquoise powder spray coat could be applied for high corrosion resistance, especially if being used in the salt water. Figure 23: Additional front suspension. Figure 22: Completed prototype. The tires used in this design are heavy-duty polyurethane air-filled balloon tires. These are ideal for use on the beach because of their light weight and large ground surface area which inhibits the chair from sinking into the sand as it rolls, much in the same way the large surface area of show shoes keep a person from sinking into the snow. 25

27 Figure 24: Polyurethane balloon tired, front wheels. The rear wheels are smaller in diameter than the front tires to accommodate for the plastic casters that we ordered along with the wheels. The casters are in the rear instead of the front, like seen in typical wheelchair designs, in order to make turning for the one pushing the chair easier. This is because the front wheels serve as the pivot point of turning, which is far from the handlebars. This allows for minimal torque required to turn the chair, again making it easier for the person to turn especially on the uneven and shifting sand of beaches. In order to interface the plastic casters to the metal frame, two square metal plates with a hollow tube cut at an angle welded to it were created. These tubes had holes cut into them that matched up with holes cut into the existing stroller frame support and would be held in place by a bolt and nut for easy disassembly. The plates each have four holes that correspond to the holes already in the plastic caster which are secured together by bolts and nuts. In order to keep these two casters from displacing from each other and compromising chair function, a collar bar with two holes was cut in order to hold these pieces in place. 26

28 Figure 25: Rear casters with aluminum interface and collar bar. A seat was constructed out of PVC pipe and divided into three sections: a back support, bottom support, and leg support. Both the back and leg supports are adjustable for Danielle s comfort and are governed by adjustable connectors with wing nuts that can be loosened and tightened to the desired configuration. Armrests were also made out of PVC and connected to the bottom portion of the seat. The entire seat is bolted securely to the existing frame seat plate in four places. This plate can disconnect from the chair frame which makes transporting easy. A turquoise mesh fabric was riveted into the PVC pipes at regular intervals to ensure a smooth continuity in the design. A simple buckled lap belt was installed for Danielle s safety while she is using the chair. Figure 26: PVC seat with mesh fabric. 27

29 As mentioned before, the wheelchair disassembles and collapses for easy transport and storage. This is initiated by two latches near the handlebars. The entire chair disassembles into seven separate pieces; there is the basic frame (including additional welded aluminum), the two front tires, the two rear casters/tires, the caster collar bar, and the PVC seat. Figure 27: Collapsed and disassembled beach wheelchair. 3 Realistic Constraints 3.1 Annalee Health and Safety The power chair that is being modified for Annalee is meant to keep her level in the chair as she traverses the terrain in her yard. Annalee has tipped one of her chairs over in her yard so the main concern is to avoid this happening again. The restraints that are built into the seat will hold Annalee in the seat, and the automatic leveling system for the seat should keep the chair balanced so that it does not tip over when Annalee is using it. Sustainability The power chair should last a number of years so that Annalee can enjoy it for that extended period of time. The chair itself is durable and if treated properly and maintained, should last a number of years. The batteries are the only thing that should have to be replaced, and the 28