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. In fact the wheeli action would drive the chair backwards, if the hand-force to lift the front wheels were to be continued. The only past way, is to stop at the curb, which is unsatisfactory because it halts all forward motion.

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. This allows continuous forward motion of the wheel-chair with minimal horizontal forces for crossing the obstacle. It does raise the front of the wheel-chair by a few centimeters, unless the modifications includes adjusting the position of 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. These 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.



David Chester wrote on June 23, 2016, 16:57 :

This was proposed in Tel Aviv TOM by David Chester on 15-06-2016.