How to create curtain-like rope simulation in Omniverse issacSIm?

[pcom-nishi]

Hello!!

In one of the videos shown in this NVIDIA video (https://youtu.be/7ozs5EsvVGE)、
there is a scene where a group of strings (like a curtain) hangs down and drapes along a colliding object.
I attached a scene.

I have a few questions about how this is implemented:

• Is this simulation using Deformable Bodies?

• How are the strings modeled?

Are they individual string objects arranged side by side?

Or is each string composed of multiple small connected objects (segments), and then those strings are arranged side by side?

• Are there any hints, best practices, or recommended approaches for creating this kind of physical simulation?

Best Regards.

[RandomOakForest]

Thank you for posting this. That “curtain of strings” shot is most likely done with many rope‑like strands built from rigid segments and joints, not a single deformable body volume.¹²

Deformable body vs rope setup

• Isaac Sim’s deformable bodies are volumetric soft objects (typically tetrahedral meshes) and behave more like soft rods or blobs than thin, highly bending ropes unless you push the resolution hard.³¹
• For long, thin strings, PhysX usually models them as chains of rigid bodies connected with joints or as 1D constraints inside a cloth/particle system, because this is more stable and controllable for rope‑like behavior.⁴²

How the strings are typically modeled

The shot you reference is almost certainly built as many strands in parallel:

• Each string is a chain of small rigid segments (capsules or short cylinders) linked by D6/spherical joints or distance constraints, with limited stretch and tuned damping.⁵²
• The “curtain” is just many of these strings duplicated and offset along one axis, all constrained at the top to a fixed bar or frame.⁵
• The visual mesh can either be each segment itself (capsule mesh) or a slightly smoothed mesh skinned to those rigid links for nicer rendering.²

You can approximate a rope using a single deformable body (a long cylinder) with a deformable component, but in practice you run into issues (looks stiff or like a rigid stick unless you use the debug visualization, and tuning gets tricky).⁶⁷

Recommended approach to reproduce this

A practical pattern in Isaac Sim / Omniverse (PhysX 5‑based) is:

1. Model one strand:
   • Create 10–40 short capsules (length small compared to total rope length).²
   • Connect them with distance constraints or D6 joints, allowing swing and twist, constraining stretch just enough to avoid “rubber band” behavior.²
2. Attach the top:
   • Fix the top segment to a static bar using a fixed or very stiff joint, or set that segment kinematic.²
3. Duplicate into a curtain:
   • Use instancing/duplication along X (or Y) to create many identical strands side‑by‑side with small spacing.⁵
4. Enable collisions:
   • Ensure self‑collision between segments of different strands and collision with the object that pushes through the curtain.²
   • Consider disabling collisions between immediate neighbors in the same strand to improve stability if needed.²
5. Tune parameters:
   • Reduce mass per segment and increase solver iterations/substeps for stability.²
   • Add a bit of damping in joints to remove jitter and get that smooth draping behavior.²

Best practices / hints

• Prefer many short segments over few long ones; this reduces kinking and makes draping look smooth, at the cost of more DOFs.²
• Keep ropes fairly light compared to the colliding object so the object can pass through the curtain without exploding the simulation.²
• Use CCD (continuous collision detection) for fast moving colliders that pass through the strings.²
• If you later move to Isaac Lab, you can wrap this in a custom asset class (e.g., constructing the chain programmatically) rather than authoring each segment by hand.¹

This summary is still under review.

Footnotes

1. https://isaac-sim.github.io/IsaacLab/main/source/tutorials/01_assets/run_deformable_object.html ↩ ↩² ↩³

2. https://forums.developer.nvidia.com/t/cloth-simulation-using-physx-sdk/191400 ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴

3. https://www.youtube.com/watch?v=Qp-4DqUrjmY ↩

4. https://github.com/NVIDIA-Omniverse/PhysX/discussions/328 ↩

5. https://forums.developer.nvidia.com/t/wire-and-ropes-simulation-in-isaac-sim4-5-or-4-2/333863 ↩ ↩² ↩³

6. https://forums.developer.nvidia.com/t/simulating-a-soft-rope-in-isaac-sim/318071 ↩

7. https://forums.developer.nvidia.com/t/can-isaac-sim-simulate-a-rope/311915 ↩

[pcom-nishi]

Thank you for your reply.