Sorry, a bit more clarity.
The current setup has a 90v 15:1 motor being controlled by a quantum electronics board. This board is handling the power supply (240v ->90v @ 3a) This board also is handling the PWM controlling the speed. The speed is determined from a 10k Pot (multimeter reads 3v across it)
All I want to replace ideally is the 10k pot which controls the speed of the motor.
I want to replace this pot completely so that rather than having a knob with which to adjust speed, I can write a program to change speed over time or according to other conditions.
I hope thats a bit clearer.