reverse motor polarity

We are making our own y splitter for motors from 2 extender cables. We need the polarity reversed on one of them and so we figured we would just reverse the black and red wires and leave the white wire alone as it carries the control. However, it isn’t working for some reason. any idea why this could be? thanks

Between the Microcontroller CPU and the output shaft of the motor, the commands to the motor start out as pulses. It is the width of these pulses that determines whether the output shaft will turn CW or CCW, not the polarity of the wires carrying the pulse information.

I’m not 100% sure where the pulses get converted into the voltages that make the motors spin and make the servos move, but I’ll bet a nice lunch (99.9% sure) that it occurs on the motor-side of your Y-cable, not on the microcontroller-side.

That means that instead reversing the motor’s spin direction, you are feeding the pulse decoder bad-polarity (upside down) pulses, and it is unhappy.