Jitter at low speed no load.

I’m using XL430-W250-T servo with OpenRB-150 and a beefy 12V DC power supply. I have a light 6" x 9" piece of cardstock attached to the hub with screws in horizontal orientation. When I run the servo at 1 RPM in OP_VELOCITY mode, there is a noticeable speed jitter. The servo is using the default PI parameters. Is there anything I can do to make the speed more uniform?

Do you still experience the same jittery motion with a higher goal RPM? If that doesn’t result in a more smooth rotational motion would you be able to share a video of the issue, and any more information you could share about your control solution/program to assist with troubleshooting

I played with motion parameters and was able to achieve subjectively smooth motion down to 1 RPM. I used these parameters:

  dxl.setOperatingMode(1, OP_VELOCITY);
  dxl.writeControlTableItem(VELOCITY_P_GAIN, 1, 1000);
  dxl.writeControlTableItem(VELOCITY_I_GAIN, 1, 1000);
  dxl.writeControlTableItem(PROFILE_ACCELERATION, 1, 1);

I think the culprit was a default setting of PROFILE_ACCELERATION to its maximum value, which causes jerky speed corrections. My application was an art installation, where accurate speed is not a concern, but any motion jerkiness is a show-stopper.

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I’m glad you sorted it out, and that makes a lot of sense. I had assumed it would be something like the internal controller just having a hard time keeping such a low RPM consistent.

I’m also curious to hear about your project if you would be able to share it. I’m always interested in seeing the interesting stuff artists can create using DYNAMIXEL actuators.

Sorry for a late response - I didn’t get email notification about your post. I was consulting for the artist, who is still working on the project.