Unity.Physics joints behaving oddly with colliders

[NonPolynomialTim]

I am somewhat inexperienced with physics joints, so I may be missing something incredibly simple, but I’m experiencing some odd behavior in my game with hinge joints, which you can see on the top gear in this video:

Unity.Physics Joint Behavior with Colliders

At the start of the video the gears look fine, but when I enable the collider on the top gear it starts to move erratically and rotate in the opposite direction. If I disable the collider it goes back to rotating smoothly as expected.

I am trying to create a planetary gear setup like this:

In hopes to get the middle (planetary) gears to both revolve around the central (sun) gear and rotate on their own, I’m using a hinge joint with the following setup. The settings I believe to be relevant are that the gear is not kinematic, it’s using a motor to rotate, and Enable Collision = false.

The Connected Body on the hinge join is an empty, kinematic rigidbody that sits in the middle of the planetary gears. The planetary gears are not parented to that empty rigidbody.

Why would the gear behave erratically and rotate the opposite direction when the Sphere Collider component is enabled, and how can I prevent that behavior?

Thanks in advance!

[NonPolynomialTim]

Reducing the radius of the SphereCollider stops the erratic movement, but the gear is still rotating the wrong direction, and it is rotating faster than the others.

[daniel-holz]

Can you add the physics debug display component and enable Draw Collider Edges and Draw Contacts please?

It’s hard to tell what is going on here without these visualizations.