Development of folding three-wheeled wheelchair frame for the Developing World

Abstract

Currently, wheelchairs in developing countries are supplied both through donations from NGOs and local wheelchair workshops in these countries. A popular type of wheelchair manufactured by these workshops is a three-wheeled wheelchair, which has a long wheel base and third castor wheel in front of the chair. These wheelchairs perform better in the rough terrain of the developing world, but do not have a folding frame, and thus cannot be transported. This severely diminishes the ability of the wheelchair's user to travel far distances and generate income. Because of this problem, this project aims at developing a frame for the three-wheeled wheelchair that folds into small dimensions similar to a traditional four-wheeled wheelchair.

(cont.) The major considerations when designing this wheelchair were weight, cost, and local availability of materials. All materials used for the wheelchair can be found in the majority of developing countries, as they consist of mild steel, bicycle parts, ABS plastic, and canvas for the seat. After evaluation of designs, a double L-brace, which very closely resembles the x-braces used in traditional four-wheeled wheelchairs, was decided upon. Being similar to these wheelchairs will increase user acceptance of this wheelchair. Analysis optimized the dimensions of the L-brace, and found all forces and moments on the wheelchair, so that the size of mild steel piping could be minimized, thus reducing both the weight and cost. The maximum moment in the center rod of the wheelchair was found to be 236.0 Nm and in the L-brace the maximum moment was 315.9 Nm. With the application of a safety factor, these values lead to the selection of mild steel piping with a diameter of 48.25 mm and a thickness of 1.5 mm for the center rod and a diameter of 60 mm and a thickness of 1.2 mm for the rest of the frame. Using these materials give a final material cost of $89.01, significantly less than the current cost of $230. The final weight is estimated to be 55.1 pounds, which is much higher than the current weight of only 45 pounds. This will be an important feature to look at in future work, and hopefully this new design can be reduced to about 45 pounds.