Why joints still translates even when translates is not allowed, and tiny force will cause huge disturbance

Mimic the Demo’s ‘Rigid-body capsules with D6 joints as ropes’

I modified the scripts to automatically generates a rope asset I want to use for my own project. However, it seems the rope is super unstabled and I tried many configuration and the rope movement is still explosive and unstable.

Some Problematic Phenomenon can be described as follow:

  1. too much translate movement along the axis of the rope. It should ideally be very minimal if not none. I already set the joint’s limit high to -1 and limit low to 1, I don’t understand why the translation movement still exists

  2. very tiny force can creates huge(explosive) disturbance

Screencast from 01-21-2024 09_31_46 PM

I have been stuck for few days, Huge thanks for the help!

[ropeCreate.py - Google Drive] (rope_generation_script)

[rope_test.usda - Google Drive](rope usda file)

Hi @octipus, can you please try:

  • Increase the number of position iterations (you can use the global settings in the physics scene)
  • Reduce the time step in the physics scene

Yes, it is much much more better, I have never thought its the issue in physics scene causing the issue

I have observing that increasing the Minimum Position Iteration Count has greatly improved the vertical oscillation, though at the compensation of computing time

However, Reducing the time step per second to (10 -100) seems to encourage the unstable explosion between link. Changing the time step per second to reaches 250 seems to suppress all the unstable behavior. Again at the compensation of computing

After reading the documentation for these parameters, it seems like a multi joint rope need a more frequent physics update for improving the stability. Thank you so much!!

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