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I am trying to create a mecanum wheels by attaching each pinion as a joint to a wheel in URDF. For this, I have rotated the pinion 90 degree(pitch) and 45 degree(yaw). When i am doing these rotations individually, things are perfect but when i am combining these, the yaw (after pitch) is rotating as if its roll. Also Roll is also working as expected.

After looking on the internet, I found this issue is something called gimble lock. If this is such a common issue, i was not able to find other similar issues related to ros2 joints.

QUESTIONS:

  • Quaternions require 4 variables to describe, how can I use Quaternions in joint tag(origin)(ros2 URDF) which only has roll, pitch and yaw?
  • The obvious solution is to use quaternions but is there any other way to handle this specifically with ros2 joints?

wheel image

Ignore the bottom wheel. Don't know why its behaving this way.

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  • $\begingroup$ One simple way is by putting a small offset on pitch (you can try like 0.1 degree). Yes it may generate small error on kinematic calculation but should be handled by the controller. $\endgroup$ Commented Jun 17, 2024 at 0:17
  • $\begingroup$ @AlbertHM still the same. I altered the pitch by around 5 degrees(85 degree). $\endgroup$ Commented Jun 17, 2024 at 15:17

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The issue is resolved. I would not call it an exact solution as it is just a workaround.

I changed the orientation of the roller using FreeCAD such that the 90 degree pitch is no more required.

Other Solutions I Tried:

  • Attach an intermediary blank link overlapping the roller link and have a fixed joint between the roller and the intermediary link. Then we could apply Pitch to that link and Roll and Yaw on the roller link. This worked well but was creating issues when setting axis of rotation for the roller.
  • As @AlbertHM said, we could putting a small offset on pitch but this did not worked for me.
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