Traditional manually powered wheelchairs require the occupant to turn the chair’s rear wheels with a pushing action. This places a lot of stress on muscles that aren’t really designed to be used in this way, resulting in everything from repetitive stress injuries and muscle pain to torn rotor cuffs, joint degeneration and carpal tunnel syndrome. To combat this, Salim Nasser of Merritt Island, Florida, has taken a backward approach and developed the Rowheel System, which allows a pulling motion to translate into forward motion of a wheelchair. This transfers loads and stresses usually placed on weaker shoulder and arm muscles onto more capable muscles in the upper back, shoulders and arms to reduce the chance of injury and give the user an overall increase in endurance and range.
The Rowheel system, so named because of the rowing motion employed by its users, looks similar to existing manual wheelchair wheels and can be mounted onto any standard manual wheelchair without modification to the existing wheelchair frame. It can also be easily removed or docked through a universal docking axle to allow the user to quickly disassemble the wheelchair for portability.
The key to its design is a planetary gear system at the center of the wheel that reverses the pulling motion of the user into a forward motion of the chair. The user pulls a standard rim, which is connected to the sun gear of the planetary system. This engages the planet gears (the planet carrier motion is fixed to the chair frame), which in turn engage a ring gear that is fixed to the hub that is fixed to the wheel via spokes. Large bore, small cross-section bearings fixed on to the inner and outer hub plates, allow relative motion between these plates and the inner and outer hub casings to occur.
Nasser, who is himself wheelchair-bound, originally designed the system as his senior design project while attending Florida International University (FIU), with the original design taking four and a half months from concept to prototype. He says its construction involved relatively simple manufacturing with the prototype’s tires, rims, spokes and bearing purchased from third-parties, while the gears and hubs were cut in-house. He says a commercial version would use an all-in-one carbon fiber outer hub/spoke/wheel rim for decreased weight, ease of assembly and visual appeal.
The Rowheel System was named the winning entry in the Create the Future Design Contest that attracted nearly 1,000 product ideas from engineers and students in 51 countries. In taking out the grand prize, Nasser, who is currently an engineer at NASA’s Kennedy Space Center where he performs structural and dynamic analysis for flight hardware and ground support equipment, will take home US$20,000.
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