Deformable rops is settling sideways even under influence of gravity

Omniverse Isaac Sim
1

Deformable stem is doing one sided swing motion without any input.

Steps to reproduce: USDA file uploaded. Run on Isaac Sim 5.1.0

reproduce_but.zip (5.5 KB)

6.0.0
5.1.0
5.0.0
4.5.0
4.2.0
4.1.0
4.0.0
4.5.0
2023.1.1
2023.1.0-hotfix.1
Other (please specify):

Operating System

Ubuntu 24.04
Ubuntu 22.04
Ubuntu 20.04
Windows 11
Windows 10
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GPU Information

  • Model:
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The setup is supposed to be of a simple deformable rope hanging via attachment. The lower end of the rope is attached to a dummy invisible rigidbody. This dummy body then connected to a fruit ( sphere ).

When I run the simulation, the rope dangles for a moment then visibly settles/keeps swinging in favour of one sideway direction. Not even back and forth.

3

Hi @donkumar727,

The sideways settling is caused by asymmetric attachment points on your deformable rope.

The PhysxAutoAttachmentAPI picks collision mesh vertices near the overlap region
between the rope and the connector. Your collision mesh has only 25 vertices (from
collision simplification), and the selected attachment points end up biased to one
side – the bottom attachment center is offset by ~2-4mm from the rope’s axis. With
a 2kg fruit hanging from a thin 0.75m rope, that offset creates enough torque to
pull the rope sideways.

Workarounds (try in order):

  1. Increase simulation resolution: Set physxDeformable:simulationHexahedralResolution to 16 or 32 for a finer, more symmetric tet mesh.

  2. Disable collision simplification: Set physxDeformable:collisionSimplification = 0 so the full mesh is used for attachments, giving more (and more symmetric) vertex candidates.

  3. Increase damping: Raise elasticityDamping from 0.005 to 0.05 or higher to
    dissipate oscillations faster.

  4. Manual attachment: Instead of auto-attachment, define your attachment points manually at symmetric positions around the rope’s center axis.

4

Hello!

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