Kimberlee Fraser, Christopher Nelson, Sean Meibers, Nathan Shinn, and Tahiem Williams
In this paper we describe an innovative design for a manually powered wheelchair. While much has changed in the assistive device industry, wheelchair designs have remained stagnant. Users are confronted by an assortment of heavy, institutionally styled wheelchairs. By utilizing the unique properties of carbon fiber we were able to design a lightweight, modern wheelchair for an active adult user. Further improving on existing designs, we expanded our project to include a complete rework of wheelchair wheels. Our resulting spoke-less wheel and single front spherical caster decrease the visual weight of the chair while also improving mobility. The final weight of our design is 22 pounds, mostly due to the spoke-less wheels. Our frame weighs less than three pounds.
The frame of our final design is best described as organic; lacking some of the right angles and sharp edges of current wheelchairs, particularly where structural components meet. Whereas traditional tubular frames are generally joined by welding together straight pieces of steel or aluminum at angles that create sharp transitions, our frame employs large radius fillets between structural elements. This results in a striking aesthetic while simultaneously reducing stress concentrations. Every joint on the design would have a filleted radius because that is how carbon fiber is manufactured. These gradual transitions between the components give our design a more flowing visual impression and imply that the wheelchair is made from a single continuous piece of material. In turn, this effectively highlights our choice of carbon fiber as the primary material of the wheelchair's construction.
In addition to its graceful form, our frame is designed to maximize maneuverability with an efficient and compact footprint. Despite the current ADA accessibility requirements for architecture, wheelchair users can find themselves in spaces that may outdate these requirements and can be more restrictive: narrow hallways, small door frames, and high profile thresholds that were once common building standards. Our frame combines a narrow width with a shorter overall length, and along with the forward caster wheel this enables users the freedom to navigate tight spaces more easily.
The spoke-less wheel is the second major component of our composite wheelchair design. It continued the effort to design a wheelchair that stood out from the rest of the industry. In standard wheelchairs, along with bicycles and automobiles, the outer tire of a wheel wraps around an inner frame which then connects to a central axle attached to the frame. In designing a spoke-less wheel an alternative method is needed. There are three main components of the spoke-less wheel: the inner frame, the outer wheel, and bearings. An outer moving wheel runs around a second circular inner frame. The inner frame would only be slightly smaller than the outer wheel, fitting inside and partially enclosed by the wheel. This would be accomplished by manufacturing the outer wheel in two parts that would then be assembled around the inner frame and locked into place through several bolts. The inner frame would then connect to the main body of wheel chair through three brackets. Between the inner frame and outer wheel would be a series of bearing surfaces. Currently these bearing series are 40 alternating bronze barrel bearings. They contact the wheel on angled surfaces, providing the bearing support while acting to keep the wheel centered into the frame.
The last major component of the composite wheel chair is the single caster wheel. Caster wheels provide full rotation for the user and allow them to get around with little effort. The bottom of the caster wheel will be made flat to increase the contact area, giving the user more control and stability. The flat wheel also prevents the user from getting stuck in small and large cracks, and it allows the wheelchair to operate on different terrains. Caster wheels are durable, easily replaceable and can withstand a large amount of weight. Although the caster wheels will improve the mobility, they may not be repairable.