I have been controlling motors through vex motor controllers that were powered by arduino.
When I tried connecting just the motor, no motor controller, to an external power supply, I could control motors in one direction (using a TIP120 transistor/Diode set up).
Changing nothing in the set up except adding the motor controller, I tried turning the transistor on and then controlling the motor through the PWM pin on the arduino. I used the same code that works fine when the arduino is powering the thing, but it didn't work. Nothing moved at all.
Does anyone have experienced using vex servos or vex motors + vex motor controllers? Everything was working so perfectly before I tried using the external power supply. I'm not sure why it isn't working.