Merritt Island, FL
There are approximately 1.8 million manual wheelchair users in the United States, and that number is expected to grow at a rate of 10% annually. Seventy-five percent of wheelchair users rely on manual wheelchairs. Prolonged manual wheelchair use is directly linked to repetitive stress injuries and pain in the upper extremities. The effects of muscle overuse become evident in the forms of muscle pain, torn rotator cuffs, joint degeneration, and carpal tunnel syndrome. There is a need to minimize these types of injuries while retaining the benefits of the exercise that these devices provide. Studies have found that continued prevalence and pain intensity over time resulted in a change in lifestyle in which the user ceased to routinely perform these activities.
The Rowheel offers a fundamental difference in the approach to manual wheelchair propulsion in that it operates by means of a pulling/rowing motion, as opposed to pushing. Biomechanically, it offers a direct and more efficient solution to the problems of shoulder, elbow, and wrist injuries, as well as user fatigue and maneuverability, since the pulling motion transfers loads and stresses usually experienced by smaller and weaker muscles in the shoulders and arms to larger and more capable muscles in the upper back, shoulders, and arms. This considerably reduces stress and injuries experienced by the shoulders, triceps, and wrists.
Said inventor Salim Nasser, with the Rowheel, “you’re putting your muscles into tension instead of compression, so it’s a better way to use your body. You minimize the effects of repetitive stress injuries by using your back muscles and biceps.”
The Rowheel has similar specifications and appearance to that of existing manual wheelchair wheels. The ability of the Rowheel to mount onto any standard manual wheelchair was of paramount importance and therefore, care was taken in incorporating standard, universal parts where necessary. According to Nasser, “Depending on what kind of manual wheelchair you have, you could add this. The main axle can be used on any chair. You may need a simple adapter plate, but you wouldn’t have to change the chair in any way.”
The key feature of the Rowheel design involves adapting a planetary gear system at the center of the wheel, which reverses the pulling motion of the user into a forward motion of the chair. The unique change from pushing to pulling, along with the mechanical advantage created by the use of the gear system, will provide an overall increase in user endurance and range.
To operate a wheelchair with Rowheels, the user pulls a standard rim that is connected to the sun gear of the planetary system. This transfers the motion from the user to the wheelchair. The sun gear engages the planet gears (the planet carrier motion is fixed to the chair frame) that, in turn, engage a ring gear that is fixed to the hub. The hub is fixed to the wheel through spokes. Large-bore, small cross-section bearings fixed on the inner and outer hub plates allow relative motion between these plates and the inner and outer hub casings to occur. The Rowheel does not require modification of existing wheelchair frames, and is easily removed or docked through a universal locking axle, allowing the user to quickly disassemble the wheelchair for portability.
A working prototype has been built with relatively simple manufacturing methods. Tires, rims, spokes, and bearings were purchased from third parties, while the gears and hubs were cut inhouse. 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.
Said Nasser, “The idea is to make this affordable for everyone. There are power-assisted wheels that can cost about $6,000, which is three times what a manual wheelchair costs. The Rowheel could give people the enhancement a powered wheel offers at an affordable price.” His hope is that “winning the contest will shed some light on the design of the invention, and find someone to partner with me on the development, as well as manufacturing and selling it. I’m not interested in becoming a millionaire from this idea. It would be nice if it could be used — not just sit in a shop gathering dust.”
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