Motor PWM signal, how far can it travel over the control cable?

jdolecki

My robot has several motors. So should I keep the motor drivers close to the Propeller and have long motor leads and short PWM cables?

or

Should I keep the Motor driver boards close to the motors and have long PWM and signal cables?

or

It dosent make a difference?

or am I think to much about this?

Mike Green

Well, you win some and you lose some either way. The leads from the driver boards to the motors carry high current and pulsed high current particularly. They're going to radiate noise all along their length and it will be substantial. There'll also be resistive losses of electrical energy into heat rather than motion. You can mitigate these by used shielded thick cables for any significant distance. On the other hand, if you have long signal (PWM) cables, they'll be susceptible to pickup noise and there may be signal distortion from distributed RC effects. This can be mediated by shielding those cables and keeping the PWM frequencies in the low KHz and Hz range. You can also, if the distances are long enough, use a higher voltage signaling like RS232 or balanced signaling like RS485.

My bias would be to keep the drivers close to the motors (and the batteries close to them both) to minimize the high current high frequency cabling and start with twisted pairs for the signals making sure to not run them near the power cables and not in parallel with them for any distance. I'd get (borrow) a scope to look at the signals on the signal cables and shield any that look sloppy. If that doesn't help enough, I'd use some buffering at either end depending on what signals are being carried, how fast they have to switch, etc.

jdolecki

Thanks Mike.