Good overall summary report, and good level of detail on system performance and comparison to benchmark systems. Some additional discussion of the kit aspect of the project and actual user testing would improve the report. Some editing errors are still present.

All-Terrain Wheelchair System Team 3 - Assistive Adventures June 2nd, 2011

The Assistive Adventures team, throughout a yearlong senior capstone project, was able to imagine a wheelchair suspension system, design its components, and manufacture a final product for the team’s client, Jimmy King. Using a process of scoring and elimination, the best possible concepts were screened and reformed through a number of iterations. Design was completed by a rigorous examination of loading situations, functional operation, and application. High tolerance machining and cost effective manufacturing was completed at the final stage of the project. The completed final design met or exceeded the pre-determined specification, resulting in a high quality, versatile off-road wheelchair suspension system. Testing of the system allowed direct comparisons to be made with respect to existing commercial wheelchairs. The results of these tests showed that the team’s wheelchair system exhibited superior performance, particularly with regard to force translated to the user. Although one of the main goals of the senior capstone project was to evaluate and solve a real world engineering problem from a business perspective, this project meant so much more to the team. Helping the team’s paraplegic client enjoy the outdoors, and return to his active life style and lead a more normal life is far more rewarding.

1.0 Introduction The wheelchair has been in existence for hundreds of years, but the modern wheelchair was not invented until the 20th century. In 1933, two mechanical engineers developed the design for the first wheelchair that was both lightweight and collapsible. The inventors were Harry Jennings and his disabled friend, Herbert Everest. They founded Everest and Jennings and for a short time, had a monopoly on the wheelchair market.[1] Since then, wheelchairs have come a long way; becoming lighter, stronger, and better suited for everyday use. Modern wheelchairs are available in two distinct types: collapsible and rigid. Collapsible wheelchairs are comprised of several pieces held together by various brackets. Rigid body wheelchairs are welded and inherently lighter due to the reduction in materials. Wheelchairs are made of various different types of materials. Older models are typically made of steel or aluminum, where more current chairs are made of materials like titanium.[1] Wheelchairs are either manual or electrically propelled by motor and battery. According to Veteran’s Affairs, as of 2008, 2.2 million United States citizens spend every day in a wheelchair.[2] Most manually propelled wheelchairs are of the rigid body type, which creates many problems and dangers for wheelchair users. Rigid bodied wheelchairs are inherently unstable due to their inability to flex, which causes the loss of four points of contact (four tires) on uneven surfaces. If four points of contact is not maintained, the chair can become dangerously unstable, which is not ideal for an individual who lacks full leg and torso control. Various companies have developed systems to help alleviate this problem. The main problem with mass production of specialty wheelchair accessories is price; they are generally extremely expensive due to the specialty and custom manufacturing required. The purpose of the project was to design and implement a safe, effective, and less expensive modification system that helps the user maintain stability on “non-ideal” surfaces. Although a system of this sort could be used by many, this specific one was designed for the client, Jimmy King. Jimmy is a 21 year old man from Pickerington, OH. Following a motocross injury, he was left paralyzed from the chest down and depends on a wheelchair for his everyday life. Jimmy has a love of the outdoors, and is an avid fisherman. Having a rigid body wheelchair, Jimmy finds much difficulty maneuvering through the rough terrain of the outdoors and even everyday obstacles such as gravel, large cracks, and common street curbs. Research conducted through the Center for the Study of Aging and Human Development at Duke University and the Department of Occupational Therapy at the University of Toronto show that there is a large increase in wheel chair users in the last 20 years in both the United States and Canada. [3] The elderly community is the largest representative group using assistive technology. Other factors, such as veterans returning from war and bodily injury, only increase the number of wheel chair users in need. Due to this, there is a need for a more suitable system to allow manual wheelchair users to be more comfortable and maintain their independence. A study published in the Journal of Rehabilitation Research & Development concluded that the addition of suspension to rigid wheelchairs decreases forces and accelerations experienced by the user, especially users void of trunk control like Jimmy. [4] A conclusion can be drawn that the addition of suspension to the client’s wheelchair will not only improve his comfort while in the chair, but increase the limits of what he is capable of. The development of an inexpensive and easily adaptable system will further increase the independence and scope that wheelchair users hold in society.

2.0 Needs Statement Due to the inflexible nature of rigid body wheelchairs, there is a need for a wheelchair modification to increase mobility on “non-ideal” surfaces. Such terrains include (but are not limited to): gravel, grass, dirt, and cracked asphalt or concrete. A wheelchair modification is required to traverse these types of terrains while keeping four points of contact between the wheels and ground while also maintaining stability and comfort for the user. In addition to these stipulations, it was required for ADA wheelchair standards to be followed in order for the system to be suited for everyday use. 3.0 System Goals In order to have a safe and effective solution, the system had to be designed to meet certain performance specifications. The main goal of the project was to keep four points of contact (all four wheels) with the ground on non-ideal terrain. It was decided that “non-ideal terrain” qualified as a surface with a maximum undulation of four inches or less, because this is a common, manageable height. Some of the system’s other goals included an overall weight addition of less than 25%, easy installation (less than 4 hand tools), maintaining the proper seat angle (dump angle), and to increase the wheelbase for greater stability. 4.0 Preliminary Conceptual Design Since the team’s goal was to create designs that could keep all four wheels in contact with the ground, it was decided that a suspension system must be designed for the client’s wheelchair. The team next completed background research as to possible solutions and/or existing solutions to the problem. This was done by performing patent searches and scouring various other resources for information. Several patents were examined to help develop concepts, as well as, determine what intellectual properties are currently held by patent holders. Specifically, two patents make claims which cover a very broad area of wheelchair suspensions; coincidently, both have expired, meaning the team has very little risk in patent infringement. Once a complete understanding of both the problem and possible solutions were obtained, the team outlined requirements which each concept must meet to move on for further consideration. 5.0 Concept Screening Initial concept requirements were quite generic; consisting of design type and overall feasibility of the idea. The team created these simple requirements to distinguish the type of design and if the concept was something that could be made and would perform adequately at first glance. The subsequent brainstorming was done on an individual basis. Concepts were created for rear suspension, front arm extensions, and a possible braking system for the wheelchair. It should be noted that the team decided that a rear suspension system was the primary design aspect of the project, since the rear wheels are what drive the wheelchair; if any contact is lost here, forward movement cannot be attained. The front suspension and the braking system were secondary goals, but were still highly important. The team came up with 28 total concepts for preliminary consideration. Initially, through application of feasibility standards, the team eliminated 7 of the concepts. Concepts were then screened through 3 criteria; feasibility, cost and ease of manufacturing. Many concepts were eliminated based upon group discussion of functionality. Customer feedback was a foremost priority in our conceptual design process. Several times throughout the process Jimmy was contacted in order to determine if a possible solution was appropriate based upon his standards. Continuing through the process to the final three concepts, a survey was sent to Jimmy with sketches of each idea. An overview of the operation of the system with labeled diagrams was sent along with this; his feedback was also requested. Jimmy’s feedback is extremely valuable to the team, and helped with the final design decision.

6.0 Function

The designed system allows for significantly more maneuverability on uneven (off-camber) terrain than the client’s stock wheelchair. One fashion in which the suspension deals with off-camber surfaces is through independent movement. As seen in Figure 3, the user is on a slope of approximately 10 degrees. As the right shock compresses and the left relaxes, the chair is able to level itself, offering more stability to the user. Furthermore, the chosen shocks allow for independent control of spring rate and damping ratio, allowing for this to work in a stationary situation as well.

Figure 3: Independent Suspension Travel Other obstacles will also call for the suspension to work independently. For example, a piece of wood or a crack in the sidewalk can be easily navigated with the suspension system. As seen in Figure 4, the right side of the wheelchair must articulate upwards in order to maintain 4 wheels on a surface, while moving over the obstacle. The right rear shock compresses, while the others adjust to equilibrium, allowing for all four wheels to have some type of contact, and a resulting high stability.

Figure 4: Independent Travel Over Obstacle

The user will also have to navigate obstacles in his daily life. Some of these obstacles demand independent wheel articulation, whereas others require the shocks to work in unison. A common obstacle that wheelchair users must face (or avoid) is the street curb. Assuming the user is traveling a path perpendicular to the curb, the wheels will act in unison as the back end of the chair rolls off of the curb, with the suspension absorbing the force. This is not a maneuver that could be comfortably or safely performed in a standard rigid wheelchair. 7.0 Final Rear Suspension Concept Through careful consideration, calculations, FE analysis, and close work with the client, the final design was built as a solid model, as seen in Figure 1:

Figure 1: Final Design Exploded Rear Assembly The final design for the rear suspension consists of several parts. Essentially three categories of components can be found in the rear assembly: moving parts, supports, and fasteners. In regards to moving part, there is a rotating link and shock. The supports consist of the rigid link, the camber tube, support tube, and the support clamp. Finally the fasteners include the two shoulder screw axles, the frame clamp, and the screws the hold the rigid link to the frame clamp. The system is quite simple in function, although it may look fairly complicated on paper. All support components are basically based off of the rigid link. The frame clamp is what secures the entire system to the stock wheelchair frame and allows for quick removal of the entire system. The rigid link is held onto

the frame clamp by for ¼-20 flathead bolts, and is located by two pressed location pins on the frame clamp. The rotating link and shock system is what allows the vertical articulation in the wheels. Two shoulder screws were used to both support the rotating link and shock and to act as the axles for them to pivot about. A closer look at this system can be seen in Figure 2:

Figure 2: Rotating Link Exploded Assembly

8.0 Manufacturing The main components (rotating and rigid links, frame clamps, etc.) of the system were mostly machined, whereas all secondary components (tires, fasteners, etc.) were purchased. A table of the major components can be seen below, in Table 1:

Component Frame Clamps Rotating Links Rigid Links Front Extensions

Table 1 : Major Component Manufacturing Details Material Dimensions Manufacturing Process 6061 Aluminum (2) 2"x4"x4" Blocks CNC Mini Mill 6061 Aluminum (2) 2"x2"x12" Bars CNC Mini Mill 304 Stainless Steel (1) 12"x12"x1/4" Plate CNC Mini Mill and TIG Welder 60601 Aluminum (1) 2"x4"x24" CNC Mill Mill

9.0 Final Product

The final, delivered prototype is pictured at the left. This complete prototype includes the designed suspension system, all-terrain tires, front wheel extensions with larger, wider wheels, a padded seat support, and pinch point protectors for safety. It is important to note that no modifications have been made to the wheelchair frame in any fashion; it can be returned to its stock state in approximately 10 minutes. There are 4 hand tools required for installation, which were included in a tool kit, given to the client. This kit also included an air pump to pressurize the shocks for proper use. Ideal pressure ranges were produced for the client’s use, which were determined through testing. Figure 5 : Final System A detailed image of the rear suspension system can be seen in Figure 6. This image shows the rigid link supporting the shoulder screw axles, about which the shock and rotating link rotate. The wheel has a quick-connect feature and attaches at the point on the very end (black sleeve) of the rotating link. As the wheel goes over an object, the rotating link acts as a moment arm, compressing the shock and allowing for vertical articulation. The rigid link is attached to the wheelchair by the frame clamp. The link is positioned by two locating pins and fastened with 4 ¼-20 flathead bolts.

Figure 6 : Rear Suspension System

An image of the frame clamp assembly is pictured at the left. The clamp allows the entire system to essentially “drop out” of the bottom of the chair. Each clamp is held by four ¼-20 cap bolts, which can be easily removed with a 3/16 Allan wrench. The frame clamps also hold the main axle (camber tube) of the chair, giving it lateral stability. As stated earlier, the clamps are in the same location as the stock clamps, ensuring that the loading situation is acceptable.

Figure 7 : Frame Clamp Assembly

The front extension arms were integral to the success of the chair’s stability. These arms allow the chair to conquer ledges much more easily and give a significant amount of stability to the user. Although the turning radius is slightly larger, the chair still easily meets ADA standards for commercial wheelchairs. In addition to the extensions, larger wheels and casters were used in the final design. These wheels are foam filled and are four inches larger in diameter than the stock wheels. These allow for more maneuverability through rough terrain, as they disperse the forces more readily than the stock, hard plastic wheels.

Figure 8 : Front Extensions and Casters

10.0 Design Testing Wheelchairs with suspensions is not a new idea, several companies manufacture and sell off-road wheelchairs. These systems generally cost on the order of $3,000-$10,000, depending on the sophistication and quality. Unfortunately, most insurance providers only help their handicap clients’ purchases one chair if they are lucky, meaning a second, off-road chair for instance, would be paid for out of pocket. One aim of this project is to compete with these existing systems and bring a quality suspension system kit at an affordable price. One commercial method which determines the quality of suspension design involves measuring the absorption of force from a curb decent. To compare the team’s chair to existing systems, a test was setup to measure absorption. The chair was tested with and without the suspension system. The results can be seen in Table 2, below. Table 2: Drop Test Data Maximum Acceleration from 3"(7.62 cm) Drop (m/s^2)

Rigid

User

Weight

Average

Todd

160 lbs - 712 N

47.1

Anthony

170 lbs - 756 N

47.3

Slade

185 lbs - 823 N

47.0

Brad

205 lbs - 912 N

47.4

Average

N/A

47.2

Maximum Acceleration from 3"(7.62 cm) Drop (m/s^2)

Suspension

User

Weight

Average

Todd

160 lbs - 712 N

25.9

Anthony

170 lbs - 756 N

28.2

Slade

185 lbs - 823 N

25.6

Brad

205 lbs - 912 N

23.7

Average

N/A

25.8

From these data tables from the test, it can be concluded that from a 7.62 cm curb decent, the suspension system reduced the maximum acceleration by nearly 50% as compared to the rigid or original system.

Table 2: Commercially Available Systems Comparison [5] Comparing the team’s testing results with the scientific study shows that the data from the rigid test match; meaning the method of comparison is relevant. Looking at the suspension comparison, it can be stated that the team’s suspension system easily compares and actually beats several existing suspension wheelchair systems. This validates the design and proves that the off-road wheelchair kit is more than capable of competing with industry. 11.0 Conclusion The Assistive Adventures team, throughout a yearlong senior capstone project, was able to imagine a wheelchair suspension system, design its components, and manufacture a final product. Using a process of scoring and elimination, the best possible concepts were screened and reformed through a number of iterations. Design was completed by a rigorous examination of: loading situations, functional operation, and application. High tolerance machining and cost effective manufacturing was completed at the final stage of the project. The completed final design met or exceeded the pre-determined specification, resulting in a high quality, versatile off-road wheelchair suspension system. Testing of the system allowed direct comparisons to be made with respect to existing commercial wheelchairs. The results of these tests showed that the team’s wheelchair kit exhibited superior performance, particularly with regard to force translated to the user. Although one of the main goals of the senior capstone project was to evaluate and solve a real world engineering problem from a business perspective, this project meant so much more. Helping the team’s paraplegic client enjoy the outdoors, and return to his active life style and lead a more normal life is far more rewarding.

12.0 Bibliography [1] "Wheelchair." Wikipedia, the Free Encyclopedia. Web. 19 Oct. 2010. . [2] "Comparison of wheelchair wheels in terms of vibration and spasticity in people with spinal cord injury Journal of Rehabilitation Research & Development". 45. (2008), 1269-1280, [3] Philippa Clarke,Angela Colatonio, "Wheelchair users Among Community Dwelling Older Adults ." Canadian Journal on Aging 2, no. Issue 24 (2005): [191-198]. [4] Philip S. Requejo,PhD;Gregot Kerdanya,MS;Jean Minkel,PT;Rodney Adkins,PhD;Robert Waters,MD, "Effect of Rear Suspension and Speed on Seat Forces and Head Accelerations experienced by Manual Wheelchair users ." Journal of RehabilitationResearch and Development 45, no. Ussue 7 (2008): [985-996]. [5] Andrew M. Kwarciak, MS;1–3 Rory A. Cooper, PhD;1–4* Shirley G. Fitzgerald, PhD1–2, “Curb descent testing of suspension manual wheelchairs.” Journal of Rehabilitation Research & Development Volume 45,, Number 1, 2008 [73–84]