(Click on the pictures to see full-size images).
Way back in early 2005 it became apparent that electric pedal assist (pedelec) would greatly prolong my use of bikes for transport. So, at the age of 57 I built a recumbent bike with electric wheel hub motor (See detailed description here).
Now, in 2022 it was clear that the spare hub motor I had bought for this bike, and which had never been used could be put to a different purpose.
The hub is an early version of the BionX 24 Volt, 250 Watt motor that can be operated with a throttle console on the handle bar. The mechanical construction is very simple having only one moving part - the outer rim to which the wheel spokes are attached - while the electro-magnets and electronic control are stationary. The basic construction can be seen in the photograph above, where the hub has been spilt in two parts by removing the retaining nuts on the axle.
In the Benelux these are also referred to as a "step" or "autoped" (Ned) or more elegantly "trottinette" (Fr). The low centre of gravity makes this very easy for young children to ride without falling over, but also suitable for carrying quite heavy loads placed on the platform - easy to manage for anyone.
The idea struck me that it might be possible to fit a standard 12 inch scooter tyre directly onto the BionX hub. The only problem would be that this could not work with a normal inflatable inner tube because there is no rim as such. Yet the beauty and simplicity of the idea struck me as irresistible.
Checking the diameter, it was clear that the tyre would fit perfectly if an airless microcellular foam inner tyre is used instead of an inflatable tube. By good fortune, this proved to be correct. The motorized wheel assembly is shown below, ready to be installed. The pictures below also show clearly the very simple construction of the BionX hub and how it is fitted without the need for a separte torque arm:
Now the motorized wheel could be used directly, but first a mounting bracked had to to be constructed for the motor battery. This was done as shown below, before the brazing work was painted over. Note that the motor was initially in the rear wheel:
In addition, the BionX can operate as brake by activating the strong internal magnets. This is controlled by a switch fitted to a normal bicycle brake lever. Electronic braking is very efficient with no friction, but my old scooter also has a foot-operated lever that pushes a friction pad against the rear tyre - a very effective way to stop without any high-tech!
This is possible because an electric motor develops maximum torque at standstill, and this motor being made for a much larger wheel could easily overpower the mass of the rider. However, the solution was very simple - install the motor in the front wheel. That way, when too much torque is applied, the tyre loses traction with no loss of control. Yet another problem was soon revealed: The short wheelbase, suitable for children, made it difficult for an adult to control with the handlebar very close to the body. This called for a more drastic change - to extend the length of the scooter frame itself, as shown below.
Confident that this was the final solution, a good paint job was applied. However, the longer frame was now too flexible under the weight of an adult rider. For extra stiffness a wooden insert was added under the rider's platform.
And ready to go!
Goodbye from the Gear Head.
Created: 22 May 2022. Updated: 26 May 2022