Two Stage Roller Chain Drive

To get the most compact transmission designs try using all-geared reduction stages. These are trickier to build because of the control that needs to be maintained over shaft separation and parallelism but can provide fairly large speed reductions.

The image shows a two stage straight spur gear drive transmission with a 250W electric wheelchair motor.  With, for example, two 8:1 spur gear reduction stages the arrangement would give a total speed ratio of 64:1 in a fairly compact space - good for some low speed high drive torque applications.

The straight spur gearing can also be driven from the output shaft so will not lock-up if the power is removed from drive motor, this allows the road wheel to drive the motor as a generator for regenerative braking applications.

Toothed Belt + Chain Drive

There are many possible combinations for drive elements. In an early design I tried a combination of toothed drive belt for the 1st reduction stage and a final roller chain stage to take the drive the the road wheels.

The arrangement worked satisfactorily, however it did illustrate a potential problem with toothed belt drives and that is their tendency to skip when back-driven from the larger pulley. Toothed belts are more flexible than roller chains and generally have less depth of engagement on the pulley teeth and this can produce skipping during heavy braking.

Toothed belts can however handle much higher speeds of rotation than roller chains and the arrangement may be suited for taking drive from electric motors with higher than usual shaft speeds.  They are also very quiet.

Double stage spur gear drive

Combined chain & gear drive as used in the mini garden tractor