Power-assist (mechanical modifications):
1) Direct-drive hub (for the student version of the RoughRiderTM wheelchair, svRR).
To minimize specialized parts, we use parts originally designed for single-speed bicycles. We chose not to use freewheels so that the speed and direction of the wheels may be controlled by the attached motor. Most electric bicycle motors can spin in forward and backward directions depending on the supplied voltage. That is, a positive voltage applied to the motor causes it to spin in one direction while a negative voltage applied causes it to spin in the opposite direction. With the two wheels moving in opposite direstions, the wheelchair is able to spin-in-place.
In this particular version, a 1/4″ sheet of mild steel was bent using an acetylene torch, edge of a welding table and strong arms to make mounting plates for the left and right motors. We tested slightly different geometries for the two mounting plates.