Fourth Year Engineering

Wheelchair Design
(Design & Manufacturing Engineering project, Lucy Porter)

Lucy Porter demonstrating her wheelchair designDuring a work placement at the end of her second year in Cambridge, Lucy Porter first came across the problems that wheelchairs pose for people who are hemiplegic (that is, paralysed down one side of their bodies).

"If you can only use one side of your body, then all the control and propulsive inputs for the wheelchair have to be achieved from one side," she explains. "The standard issue NHS wheelchair for this purpose is so badly designed, that it is rarely used. The two hand rims are positioned beside the driving wheel on the active side of the body, and both can be turned by the active hand. To go in a straight line using this system you need to grip both hand rims simultaneously and rotate them at the same speed. However, as you can see from the picture, the rims are relatively widely spaced, which makes them difficult to grip with one hand, especially for people with small hands and little strength. Turning is even more difficult because you use the right-hand rim to turn the left wheel and vice versa. This is very counter-intuitive and difficult to get used to."

Lucy thought that making the standard NHS hemiplegic wheelchairs easier to use was an ideal project to tackle in her fourth year. Working closely with one of the Design Engineers in the Department, Mr Samuel Lesley, a brainstorming session led to a completely new concept which is the subject of patent applications. It allows straight-ahead forward or backward motion to be achieved using only one of the hand rims, and turning on the spot using only the other hand rim. While Mr Lesley designed the propulsion system, Lucy set about designing a foot-operated steering mechanism.

Steering disengagedShe came up with the idea of using a swivelling footplate on the person's active side, as shown. When not needing to actively steer, such as when travelling in a straight line on the flat or when being pushed by an attendant, the occupant of the wheelchair can relax with both feet on the wider fixed footplate. To steer, the active foot is placed on the swivelling footplate, which allows the front wheel to be steered. The steering disengages as soon as the foot is lifted off.

Steering engaged"By carrying out this design and manufacturing project, I learned how to use a commercial CAD program for 3D modeling (ProENGINEER) and I had to do the detailed design, right down to specifying which bearings and springs to use. Getting these practical details of design right is just as important as the conceptual design."

Hopefully, in the future, many stroke and brain-damaged patients will have cause to thank Lucy and the Department of Engineering for improving their mobility.