David Chester
PROJECT: Wheel-chair curb climber

Wheel-chair : obstacle-climber : curb-climber : front : wheel : changes :

About the project:
Mechanical modification easy and cheap to make

The Problem:
When certain wheel-chairs are being power-driven or when both hands of the occupant are otherwise busy, the so called "wheeli" ability is lost--namely, to lift the front wheels up a single step or curb. The only past way is to stop at the curb, but continuous motion is now possible.

The Solution:
The design of the front wheels can be modified to give the chair a better capacity to go up a step or curb. The new arrangement incorporates 2 additional small wheels on each side. It does raise the front of the wheel-chair by a few centimeters, unless the modifications include the main-wheel pivots to make the seat level again. The design of the front wheel should try to minimize this effect. Each of the original front- wheels, is carried by a fork. The modification is by attaching to each of these wheels (or by replacing them), two curved, pivoted, flat, lever-arms. The plates are positioned as if they are forks, to carry new smallish wheels in front of and partly behind the original front wheel positions. Spacers between these lever-arms, allow room to support these two additional small wheels on axles, in the same way as the original fork did. The fork-lever is sprung (tension spring) so that the effect of hitting small obstacles is absorbed by motion to the rear of its new lower wheel. But for the curb or higher obstacles, this wheel on its fork moves further backwards and the upper end of the lever-arm, which carries the second similar wheel, then bears down at a place which lays ahead of or on the obstacle or curb. It transfers the weight (previously on the lower wheel) onto it. Then this lower wheel is relieved in its load, and it can more easily swing up and backwards and pass over the obstacle, in its turn. A wheel normally cannot cross a step of height more than about ¾ of its radius. By using the lever-arm design, the effective radius is more than doubled, allowing for easier passage and the development of considerably smaller horizontal forces when striking obstacles. The lower wheel is pushed back out of the way, causing the upper wheel to support ½ the weight on the front of the wheel on each side.