Issue with 2 XL-320 Servos

Technology
1

Hello all,

I’ve had some issues with 2 out of 25 XL-320 servos that seem to be a defect of manufacturing and I was wondering if other fellow roboticist experienced this kind of issues.

One problem is that the motor is not centered. When issuing a set_goal_position command the horn is slightly offset. This is using the low level dynamixel commands - so no interference from the offset that is possible in the motor class. You can see in the picture bellow how the notch in the horn is slightly to the right (approximately 10 degrees):

IMG_1598.JPG3264×2448 1.35 MB

The second issue, and more annoying is that the servos start to vibrate when they are sent to position 90 degrees while other positions are fine and followed (actually the range is about 82-95 degrees). Here is a video of how it behaves. The commands are in order:

  • Start from position 0
  • Move to position 90 degrees
  • Return to position 0 - closeup of the notch in the horn
  • Move to position -90 degrees; servo starts bouncing
  • Move to position -120; servo stops bouncing
  • Move to position -150; servo seems to be fine (except offset)
  • Move to position 0

https://www.youtube.com/watch?v=bUolNKOpWJc

This happens with two servos, both have the same manuafacturing stamp: 1606.

2

While the misalignment could look like the horn has been assembled at an offset, this would have required removing the little stud on the output shaft.
That would not explain the rest though, that looks very much like a damaged potentiometer.

I would suggest sending them back.

3

Thanks, that is also my assumption. Indeed for XL-320 the horn cannot be positioned at an arbitrary angle due to that stud in the shaft. I will check with the guys at Generation Robots if they can replace them.