Servo Jitter

Hey,

I'm seeing a persistent jittering coming from my servos when using the ServoPi.

Here are my repro steps:


Start program
Initialize servo position to 90 degrees
Hold for 30 seconds
Rotate servo back and forward between extreme positions for 30 seconds
Hold for 30 seconds


During the second hold for 30 seconds, the servos are jittering, and not staying completely still. It's almost as if the calibration offset has changed. But the thing is, once I disable the ServoPi and re-enable, things are back to normal, and I repeat the test only to find the same result.

So my question is - what can make this happen?

There are a few possible causes for jitter on an RC servo.

The output pulse width from the servo pi could be between two positions on the servo making it try to jump backwards and forwards between the two locations. If you are using the Servo class in our Python library you could try changing the number of steps in the move command or changing the minimum and maximum limits and see if that fixes the issue. Also, try moving the position one or two steps in either direction and see if the jitter stops.

Voltage spikes or drops on the power supply could cause a servo jitter. When the servo moves there will be an increase in the current draw on your power supply which could cause a small drop in the supply voltage. You could try adding a 220uF capacitor across the power pins on the servo to smooth the power input.

Another possible cause for the jitter is noise on the signal cable going to the servo. If the cable is picking up noise from an external source that could confuse the position circuit in the servo making it jittery. Try adding a 10nF capacitor between the signal pin on the servo and ground and see if that helps.

Unfortauntely I've decided to not use the ServoPi, I've moved on and am using pimoroni instead now - which works fine.

I may get back to this at some point, as I have two of your ServoPi boards - I'll try your suggestions, but barring the voltage drop issue you mentioned (which I've checked for already) I don't see how the other suggestions could cause the problem. The servos work fine for a short period of time, and then deteriorate after X time.