Ultimate stability

Most existing systems call for time-consuming adjustments to make the changes, often with tools and wedges. In an ideal world, it is a change that wheelchair users would like to make for themselves. The most obvious solution is to mount the wheel axle stubs on the sides of a trapezium structure. That would allow for the camber to be changed by extending or retracting the trapezium's upper or lower side. The only problem is that it then becomes a four-bar chain and therefore prone to distortion – unless at least one side and two joints are locked in position. While the uses of four bar chains are many and often ingenious, they all require a measure of inventiveness to get them to work as required, without involving massive levels of engineering and expense. The Challenge Our challenge this month is to come up with a variable camber mechanism for a wheelchair (or other vehicle) that locks solidly – in either the zero or maximum camber position – without requiring the use of tools, pins, fixing devices or loose parts that might get lost. It should also be operable by the user, not require the use of anything power driven, and be simple and low cost to manufacture. In our solution below you will find a highly imaginative solution to the problem. Simple enough, perhaps, in its concept, but innovative enough to be protected by patents. For those without access to the web, the solution will be found in our July issue. Meanwhile, if you see a better way to solve the challenge, let us know. Solution to Coffee-time Challenge Mike Spindle, managing director of Trekinetic All Terrain says, ""Like most worthy solutions, it's dead simple. The horizontal cross shaft has a left hand thread at one end and a right hand thread at the other. Turn the shaft and the nuts are driven inwards or outwards depending on the direction of rotation. The nuts contain pins, on which pivot the wheel hub carriers. The wheel hub carriers have secondary pivots attached to the seat of the wheelchair. The seat, hub carriers and shaft with the four pivots form a trapezium structure that is naturally unstable". But, "By introducing inner and outer pairs of setting screws that engage with the angled edge faces of the hub carrier linkages, in either the maximum or zero camber position, the assembly locks itself solid in either of these two positions. By restricting angular movement on both sides simultaneously, a rigid self locking framework is achieved. The screws have independent adjustment, so independent wheel setting is available. International patents have been filed for all inventions on the Trekinetic, However, Trekinetic is pleased to assist with any third parties wishing to use the devices for non wheelchair applications".TS