Eye Spyraflo, a look at bearing applications
Episode 25: Special bearings for bikes for children with special needs

For children who cannot pedal a conventional bicycle a US company decided to develop a cycle they named the ‘Step'n Go’ but to do this had to overcome some engineering problems. Unlike a traditional bicycle this innovative three-wheeled bike had to eliminate the difficult circular pedalling motion, replacing it with a more natural up and down stepping action.

The answer was to change this to more like walking than cycling to give the forward motion, but of course a bike is not just pedals, it is also handlebars, steering, and control. The engineers realised they had to change their thinking and let the riders design the cycles. The designers also involved physical therapists and one suggested tilting the steering column back towards the rider so that one of her little girls with spina bifida, would be able to fit the cycle.

But the original nylon bearing was not up to the job. The design of the steering column used a flange nylon bearing, located on a pin welded to the front axle. This caused problems for the nylon bearing, which had no self-aligning feature and would just fracture when the steering column was tilted.

The engineers searched for suitable bearings and Spyraflo provided the answer. They requested samples of the oil-impregnated bronze self-clinching, self-aligning bearing that offers a ±5° self-alignment capability. The oil-impregnated bronze bearing was chosen for its rugged construction, as well as the self-lubricating feature as this would also keep the carbon steel alignment pin from corroding.

With the Spyraflo bearing in place, the steering column can be positioned where the rider needs the handlebars, without inhibiting rotation of the column. Most children probably will not use the full 5° self-aligning feature but in tests it was used to its maximum and the steering column still worked flawlessly.

The engineers also had the added benefit in terms of cost saving and simplicity of assembly due to the patented self-clinching feature of the Spyraflo bearing. As the bearing is pressed into the bore, the tapered sides force material up into an undercut below the flange. The serration’s act as multiple cutting edges that increase the flow of material into the undercut. When finished, the flange of the bearing is flush with the surface, and becomes an integral part of the assembly.

Micromech is the UK and Eire distributor of these clever bearings, if you would like more information about them, then contact Alan Spinks on 01376 333333 or alan@micromech.co.uk