I'm trying to control the speed of a DC motor by using a potentiometer, but am unsure what value resistance I should use. Having tried 500k, 10k and 500ohms, the motor stalled almost as soon as I turn the dial (a bit more leeway with the 500ohm but not much). Rated as 12kg-cm (or 1.2 N.m) torque, with an operating voltage of 4.5-18V (rated at 12V). No load current is 70mA, fully loaded is 1380mA. Has a shaft speed of 36rpm. Not going to be using it for much so it shouldn't get anywhere near fully loaded. Any help at determining an appropriate potentiometer? Considering 3V, 6V or 9V, though 9V will probably exceed the power rating pretty quickly.