Collision not happening between MuJoCo style Ants in custom RL environment.

[jfpettit]

Hi,

I am working on porting a set of multiagent competitive environments (see the originals here: https://github.com/openai/multiagent-competition) to PyBullet and have run into a weird case where collision between Ant robots in the environment are ignored completely. The robots are able to move right through each other.

I've yet to train an RL agent in the environments, but I've been running random policies to make sure the physics look right and have come across this problem while moving the Ant robots around so they smash into each other with my mouse and by setting their initial positions so that they are near enough to hit each other.

My function in the environment that steps it is lightly modified from here: https://github.com/bulletphysics/bullet3/blob/master/examples/pybullet/gym/pybullet_envs/gym_locomotion_envs.py#L64. The modifications are specifically removing theif not self.scene.multiplayer: on L65 and commenting out lines 85 through 95. I'm not sure if either of those modifications may be having some unintended consequences, and if they are, I'm not sure how to fix them.

Interestingly, however, the Humanoid handles collisions properly and the robots collide with each other as expected. I've also tested the Humanoid and the Ant together, and those collide properly as well. The only problem appears to be when Ant vs Ant is happening.

I'm at a loss trying to figure out why this is happening and greatly appreciate any help.

Thanks!