Servos twitch when Motors get to high speed


We have the uSSC talking to 3 HS-755MG servos and 3 Victor 884 motor controllers (connected to motors). When the motor gets up to high speed, the servos twitch. On the scope, the pololu sends a rock-solid pulsewidth to the servos, but the voltage is noisy noisy noisy. At low motor speeds, we’re okay. Any ideas on how this noise is being introduced? If so… how do we stop it?!

The pololu is powered via a 5V regulator, and the servos are powered via a 6V regulator, all have common ground. (so we only take the signal from the pololu to the servos and speed controller).



I think step 1 is putting in those extra ground wires from the servo controller to the other parts. I’m not sure what the details of our power setup are, but if you are having noise problems, you really do need to think about where the currents are flowing in your ground wires because you won’t have some perfect ground with the same voltage everywhere. All of your main power branches should meet at the battery, and if you have multiple positive wires coming off the battery, you should have corresponding ground return wires, too.

- Jan

We have a marine bus terminal we plug all grounds in to. For every power lead, we have a return. I think that we need to shorten our cables and put some more capacitors in… We’re also trying to use some new 5V regulators. The one we have now seems to be un-phased by the noise generated from the motors.

EDIT: And I should point out that the signal from the pololu is still rock solid. The real problem is our adjustable regulator-- it cannot handle the noise from the motors and drops 3V when the motors are running. I don’t know if it’s because our 10uF cap is too big or what… It’s annoying because we spent $25 on that regulator! the 5V regulator is $0.44!! (7805)

But what is it they say about the right tools in the wrong hands…?

Thanks again,