Robot terminates on spawn when self-collision is enabled

[louislelay]

Hi, I'm encountering an issue where my robot terminates immediately upon spawning when I enable self-collision in the asset configuration file.

From what I can observe:

• There are no obvious pre-collisions between the robot's parts.
• The robot spawns correctly when self-collision is disabled and training works fine.
• As soon as self-collision is enabled, the environment is resetted continuously.

I've checked the URDF and the joint limits, and nothing seems off at first glance. I’ve also attached a video showing the behavior for reference.

Screencast_from_05-17-2025_042428_PM.webm

[RandomOakForest]

Thank you for posting this. The issue you're encountering is likely related to unexpected internal collisions or PhysX engine limitations. Here are a few possible causes and solutions:

1. Adjacent Link Collision Filtering

• Isaac Lab's enabled_self_collisions parameter only ignores collisions between directly adjacent links (connected by a joint). Non-adjacent links may still collide if not explicitly filtered.
• Check: Use the CollisionPropertiesCfg schema to define custom collision filters for non-adjacent links. For example:

# Explicitly disable collisions between specific links
collision_filters = [("link1", "link3"), ("link2", "link4")]

2. PhysX Kinematic State Updates

• Isaac Lab 1.2+ includes a workaround for stale kinematic states after reset. Ensure you're:
  • Using sim_utils.set_articulation_root_state() with force_kinematic_update=True.
  • Calling sim_utils.reset_articulation() after setting joint positions.

3. Self-Collision Thresholds

• For deformable bodies, verify:
  • self_collision_filter_distance ≥ 2×contact_offset
  • rest_offset is configured to prevent "resting" collisions

So in summary, it would be advisable to:

1. Temporarily enable debug_vis=True in your environment config to visualize collisions
2. Test with a minimal robot configuration (e.g., 2-link arm) to isolate the problematic collision pair
3. If using deformable components, ensure collision_simplification and collision_remesh are properly configured

This issue is consistent with a known edge case where non-adjacent links collide due to insufficient filtering. The solution typically involves explicit collision group management combined with proper kinematic state initialization.