Robot randomly explodes/jumps from ground plane

[jgillick]

I'm trying to train an 8-legged spider robot to stand with a manager-based task. For some reason, the robots seem to randomly explode off of the ground plane. As you can see in the video, it doesn't even seem to be due to any visible or large joint movements.

Screencast.from.2025-08-07.23-10-40.webm

For reference, here is my code:

• Robot USD
• Robot config
• Environment config
• PPO agent config

Based on other posts and documentation, I've tried reducing the dt value to 0.001, disabling self collisions, increased the position/velocity solver iteration counts, reduce actuator stiffness, among other things. So far, nothing has helped.

The USD model was generated from this Mujoco XML file, with this script.

I'm currently using Isaac Lab 2.2.0 and Sim 5.0

[jgillick]

Some additional information: From my experience, the simulations don't start getting unstable until about 50+ simultaneous environments. What causes this kind of instability at this number of envs? I'm running on an NVIDIA 5070 Ti, which has 16GB VRAM (if that's important to know).

I've been checking the collision bodies and nothing seems to stand out to me. Not all bodies have collisions defined, and the ones that do are either defined with primitive cylinders (for the motors) or convex meshes output by CoACD.

I was suspicious that collision meshes on the the bottom of the first leg segment might be causing the explosions when the robot is on the ground and moving it's legs (maybe the rotating mesh against the ground?). So I tried putting a box under the robot to keep the it from ever having these parts on the ground. Unfortunately, that didn't seem to help.

[jgillick]

Any thoughts? I feel like I've been running up against a wall with this, and I cannot get good training data due to it. When I run similar simulations in Gymnasium and Genesis, I don't have this issue, but I like the features of Isaac Lab better and would like to be able to use it.