This may be unrelated to some degree but I'm dying to know if anyone still remembers the old speed controllers that were simple rheostats. I want to make an RC build with used 18v drill motors with at least 20 amp drive time and everyone tells me these days that all the speed controllers are electronic parts and retarded expensive. I can't understand why it's so difficult to find a bi-polar linear rheostat outside of a high school tech class. I even went to Grainger Industrial Supply and they are simply sales clerks. Can anyone point me in the right direction for parts like this or do I have to crash the tech sec at the local college? I just want a speed controller for the 18v motor that goes both ways without a manual polarity switch so I can pull it with a servo.

All you electrical engineers... I just want a good old fashioned linear rheostat with bi-polar wiper. 18v dc drill motor. I want to control it with a servo - forward and reverse.

Wish we had more places to still buy the old stuff