Transmission is by single V-belt ( 'A" section)
A small pulley on the motor transmits power to a large 360mm pulley on the wheel.

The motor is mounted on the chassis, its centreline passes through the swingarm pivots so that the belt's tension does not vary with up and down wheel movements.

The drive ratio is easily changed for different conditions. A small set of motor pulleys provides for the complete terrain range from smooth level bitumen to undulating paddock bashing.
As an electric motor's torque is highest at standstill neither gearbox nor clutch is required.
 

The table below shows important relationships in deciding motor pulley size.
*current refers to average current during acceleration and climbing, it is very easy to exceed these figures if you are a leadfoot. Tread lightly, just enough to maintain speed. *speed refers to top speed achievable on smooth level tarmac.
 

Belt drive is less efficient than chain drive. Typically belt losses are 10% per belt and chain losses are 5%. However for large ratios using chains a layshaft may be called for, thereby raising the losses to 10%.

The main advantages I see in belt drives are:
» rugged, cheap, simple, silent and there is no need for lubrication,
» tolerant of slight misalignment,
» a belt can act as a current limiting device.

Electric motors can very quickly draw dangerously high current and burn out when stalled. I tension my belt so that it will slip at 35 Amps (adjusted with handbrake on), this still gives ample traction in all normal situations and if I hoon with too much spirit I will not damage the motor or wiring.
Lower belt tension also means less friction losses in bearings.

Some further experiences:

Freewheeling hubs have no place in chain or belt drives. They allow the motor to stop while coasting, resulting in violent shock loads when the go-pedal is depressed again.

A chain-driven Sturmey-Archer gearbox (with freewheel) was originally fitted. It did not even survive the shock loads produced in sedate constant speed Electrathon driving.

Friction roller transmission has also been tried: too many losses for a fractional hp motor.