A Pulse-Width-Modulation (PWM) speed controller has been fitted.
It replaces the original On/Off switch which was primitive and rugged yet still permitted surprisingly fine speed control once launched from a tyre smoking standstill.

PWM speed control (modulation) is achieved by electronically switching (pulsing) the power to the motor on and off very rapidly in the desired ratio of length (width) "on" slice to "off" slice.

PWM is much more gentle on the transmission.

The speed controller kit was designed by David Head.
It is installed on a massive 600 sqcm heatsink. The tip of the accelerator pedal is connected via a fishing line to the spindle of a potentiometer (at left in picture) in a voltage dividing circuit.
This voltage "tells" the controller (at right in picture) the desired speed.
2 very rugged, very intelligent proFETS effect the pulsing, they growl terribly if overloaded but still function.
(overloading is not recommended practice !)

A 50 Amp fuse, a 40 Amp overload cutout and a 0-60 Amps ammeter are fitted.
To achieve reasonable range I mostly try to not exceed 25 Amps when accelerating or climbing.
(see "transmission" page for further current limiting)