RigidBody falls through generated collision object but not BoxShape3D

Godot Version




currently I’m struggling with the following issue:

I created a large terrain in a 3D world.

  • Created with Blender
  • Imported to Godot as Wavefront OBJ

In the scene the terrain is set up:

  • MeshInstance3D with the wavefront obj set up as mesh
    • StaticBody3D
      • CollisionShape3D with a ConcavePolygonShape3D as collision shape.

I have a small object (a plate) which falls onto the terrain (made with Blender, imported as Wavefront OBJ as well).

The plate is set up as follows:

  • RigidBody3D
    • MeshInstance3D => the wavefront obj set up as Mesh
    • a generated ConvexPolygonShape3D as collision object.

Physically everything works fine, until the object is dropped into the world high enough. Then it falls through the ground, because the falling object comes in with high speed.

However, I experimented with it a bit and found out:

  • No matter what shape I use, it falls through the generated terrain shape if the collision shape of the terrain is of the PolygonShape3D. Even if it is just a huge simple box.

  • If the collision shape is a primitive shape, provided by Godot (e.g.: BoxShape3D) it works without error and the falling object is not passing through the collision shape.
    Of course I want to have more complex collision objects than just a box.

So my question is: What parameters do I need to set up, so that my own collision objects work as stable as the primitive BoxShape3D objects?

Thank you,