[techhelpbb]

All the FIRST approved motor controllers have microcontrollers in them.
The circuit to drive a DC brush motor like the CIMs with pulsed power is an analog/digital chopper.
Circuits without microcontrollers existed for decades.
Motor control chopper (generic term) come in time (like PWM) or current/voltage control.
Current/voltage control choppers have a wider range of speeds with good torque.
Complexity and wasted energy tends to increase for current/voltage choppers.

It is unclear exactly what is being looked for in this topic.
Like Ether wrote if you have a high power resistor/potentiometer/rheostat you can make this work.
However a chopper circuit is better with larger motors.
The pulsing dramatically impacts the waste heat.

You can make a relatively small speed control for a CIM sized motor without a microcontroller.
I did it for wheelchairs.
Just consider that all features require more parts.