As touched on in our recent report on F1 technology transfer, motorsport expertise has trickled into some unexpected niches, perhaps none more so than the world of wheelchair design. Wheelchairs have changed so little over the years that it is tempting for able-bodied people to think they must be some sort of optimised design-classic. In fact, that is far from the case. Although wheelchair users tend to get used to their vehicles, they have many drawbacks. A chance encounter led mechanical engineer Mike Spindle to begin designing a new wheelchair that would open up new terrains for its users, by incorporating technologies from such diverse fields as Formula 1 and office furniture.
Conventional wheelchairs, with two large wheels at the back and two small ones at the front, have a stable design but only work really well on smooth, hard surfaces. Cobbles and gravel are bad news, as are off-road tracks: the front wheels tend to get stuck in ruts, potholes and tussocky, bringing the chair to a sudden, shuddering halt. This is unpleasant for the user if they are wheeling the chair and will send an uncomfortable jolt up the arms of anyone pushing from behind. Many users find this limiting, especially outdoors.
Spindle’s attempt to solve these problems stemmed from his business. He ran a small, specialised engineering firm in Uxbridge, Middlesex, serving the automotive sector. Because this declined in the UK, the company was mostly serving the Formula 1 sector. ‘We were a subcontracting company, originally toolmakers, and we did a lot of 3D machining. Four or five years ago, the F1 teams began taking a lot more of their engineering in-house, so they weren’t talking so much to outside companies about any problems they’d been having; there were too many companies chasing not enough business.’
On the lookout for new opportunities, Spindle was inspired to turn his attention to the wheelchair after watching a young wheelchair-user struggle with his luggage at Luton Airport.
Much to the annoyance of his wife, Spindle started sketching out designs on the back of his boarding-pass, but it wasn’t until his return that he identified the exact niche he needed to design for. What was missing from the market was a portable, all-terrain wheelchair; a similar niche that mountain bikes fill in the bicycle market. Off-road wheelchairs do exist, as do sports wheelchairs of various types, but these generally can’t be used for all applications; users have to own a variety of chairs and use the right one for the appropriate purpose.
The result of the process, after six years of design, is the Trekinetic chair, featured in the recent Fast Forward exhibition of Formula-1-derived technology at London’s Science Museum.
‘One of the decisions I made right at the start was that I wouldn’t look at existing technology,’ Spindle said. ‘I started from scratch, as though a wheelchair had never existed, so that rather than trying to improve what was already there, I could create an entirely new system using the materials and the technologies I knew about.’
Spindle came up with a three-wheel design, with two large wheels at the front — which the user pushes — and a single caster at the back. The seat itself was a carbon monocoque, similar to those used as Formula 1 chassis. ‘Traditional wheelchairs have a tubular frame. The lightweight but very strong carbon-fibre seat means that we can mould it for comfort and also use it as the chassis of the wheelchair.’
The chair was the result of six years’ work and Spindle arranged for a trial at the Aspire Centre in Stanmore, a facility that helps spinal-injury patients rehabilitate and learn the new skills they need. Wheelchair users were invited to come along and try the chair, and were generally very enthusiastic — until Robin Gibbons turned up. Gibbons, a former pilot and diver with an interest in technology, sat in the chair and sent it careering across the Aspire gym at high speed. At this point, Spindle realised that the new chair was about as stable as a shopping trolley. The rear caster wobbled alarmingly and the chair refused to move in a straight line.
After going back to the drawing board, Spindle devised a spring-loaded self-centring device for the rear caster. Unless the user applies steering force to the wheels, by pushing one harder than the other, the rear wheel remains aligned in a straight line; and as the chair comes back to moving straight ahead, it clicks back into place. ‘This is the one feature that makes the three-wheeled configuration actually work,’ he added.
Making the chair suitable for multiple surfaces also led to redesigning. Although the original version was faster than a standard model over rough ground, as the ground got rougher, the chair slowed down and became less stable. What was needed was a cambered wheel, similar to those found on sports chairs: the wheel is angled to give a wide wheelbase, with the top closer in to the user. But wide-cambered chairs are no use for everyday: they won’t fit through doorways.
The camber could be made wider by unbolting the wheels and adding wedges or other devices, but this was no good for Spindle — he wanted something the user could adjust themselves, even if their mobility was limited. The answer was to mount the wheels on brackets, hinged at the top, with a universal joint at the bottom where the wheel axle joins onto the wheel. The axle incorporates a twist handle that lengthens it, increasing the camber from zero (vertical wheels) to a maximum of 24 degrees — a wheelbase increase from 71 to 87cm.
Another innovation came with the shaft that ran from the back of the seat to the rear caster. Originally this was solid, but the design team found that the chair performed better uphill with a long strut and downhill with a short one. ‘We needed an adjustable strut, perhaps a telescopic one that could be locked into position. But what a pain, to have to do that every time you wanted to go up or down a steep hill,’ Spindle said. ‘But as our designer slumped back in his chair, we noticed that the chair had a shock absorber that was adjustable by pulling a lever.’
Spindle asked a shock-absorber maker to design a pressurised-nitrogen absorber. To recline backwards, the user presses a lever and leans back to let their weight shorten the piston. To go forwards, they press the valve and lean in that direction and the gas pressure pushes the back of the chair up.
Each of the chair’s driving wheels has an independent brake to allow the chair to be steered at speed, by braking one wheel more than the other.
The chair isn’t without drawbacks: the wheel position in front of the user requires different movements to push than a standard chair and a different set of muscle groups. Users tend to find their own ways of overcoming obstacles — some, for example, find it easier to go up kerbs backwards.
But interest has been brisk, with a long waiting list in the US. ‘We expect to be in profit this year, three years after the official launch,’ Spindle said.