Wheelchair users with full use of their arms generally don't need electric wheelchairs ... but sometimes, especially if those users have long distances to cover, it sure would be nice to have one. Instead of going out and buying themselves a full electric wheelchair, however, those people may soon have the option of using a WHILL. Recently spotted by Gizmag staff at the Tokyo Motor Show, the prototype device clamps onto the wheels of an existing manual wheelchair, temporarily providing it with electric drive.

The WHILL incorporates two circular "hubs" (for lack of a better word) that attach to the outside center of both of the wheelchair's wheels. These hubs are joined by a curved control section, which bridges over the user's waist. The angle of that section can initially be manually adjusted by the user, then locked into place by locking the hubs onto the wheels.

Each of the hubs contains a separate 24-volt motor, powered by a lithium-ion battery pack. These turn the chair's wheels, propelling it up to a top speed of 20 km/h (12.5 mph). The battery reportedly takes two hours to charge, and offers a range of approximately 30 kilometers (19 miles).

Not unlike piloting a Segway, users steer by leaning in the direction that they wish to travel, with a force sensing mechanism in the control section varying the rotational speed of the wheels accordingly.

WHILL the company, which is based in Japan, is now looking for wheelchair users to help field test the device. Those users' feedback will influence the design of the final, commercial product.