I imported an stl file into mujoco. And the stl file contains a box with a hole. I tried to make a ball free fall, and the ball cannot get into the hole. I think maybe mujoco ignored the hole when performing the collision detection. I wonder if it's possible to remove the hole part from the collision detection. Thanks.
MuJoCo replaces every mesh with the convex hull of the mesh for collision purposes. If you want to model a non-convex body, you need to decompose it into multiple convex pieces, and define the pieces as geoms attached to the same body.