The purpose of developing this product was to directly and successfully solve the problem of traversing on loosely packed sand in an elegant manner. With the advice of Stephan Koehler (a WPI assistant professor), and other experienced engineers, we decided that the factor that would make the device the most successful is a high surface area to weight ratio. It was determined that surface area is the most critical parameter when trying to keep a person on a wheelchair on top of the sand.
Previous designs that add surface area to a tire on a wheelchair are noticeably inconvenient for the user. Devices that are already developed are mostly permanent structures that are added to a wheelchair. Some designs that compensate for the sand issue are entirely new wheelchairs. Because the devices are permanent and inconvenient for the users, a new, more elegant, solution has to be devised.
The final solution that we are proposing is an attachable wide-tread tire system. Briefly, the system will consist primarily of two wide wheels that attach to the existing tires on the wheelchair. These attachable wheels will be slightly less in diameter than the original wheels so that when the wheelchair is not on sand, only the original tires will be contacting the ground. There will be wide skis that attach to the front tires so that the entire wheelchair remains level.
As mentioned above, there will be two attachable tires that will be wide enough to support the user over the sand. The tires that will be utilized in the design will be modified car tires. Car tires would be normally too heavy for our purposes, so they will be stripped and strengthened so that it can be used on a wheelchair. The tires will be mounted to the axle with an aluminum mount that is bolted to the attachable tire. The mount will be made of a lightweight metal, such as aluminum, as to make the design as light as possible. The mount will also include a nylon rope. This nylon rope will be used so that the tire can be connected directly to the spokes of the original tire and so that it remains rigid as the user propels him/her self forward. The outer attachable wheel will be less in diameter than the original wheel so that when the wheel chair is on hard ground, the low surface area tire will be in contact with the surface. Also, this feature allows for the user to attach the wheels onto his/her wheelchair without difficulty. The user will be able to move forward with use of the original tires as handles. The estimated cost of development is $75.00.
The front tires of the wheelchair, if not accounted for, would make the entire design unsuccessful. Thus, there has to be an attachable ski for each of the front tires. Each ski will be twin tipped so that the user will be able to move forwards and backwards. Also, the skis will be attached with a mount and a rope. It will be similar to the mount for the larger tires.
Before the final prototype is built, experimentation will be done at a beach to determine the optimal width of the tire for our client’s body weight. The data will be analyzed to form trends that will be able to describe exactly how wide the tire should be. An optimal tire pressure chart will be determined for various conditions. In conclusion, a design that cleverly adds more surface area of a tire onto a normal wheelchair will be developed.