Need second pair of eyes: rigidbodies with colliders not firing OnCollisionEnter yet again...

[ZoopTEK]

It’s gotta be something with the parent/child relationships:

Nothing fancy here:

GameObject 1:
    -Capsule collider with Is Trigger DISABLED.  I want physics reactions.
    -Rigidbody with Is Kinematic DISABLED.  I want physics reactions.

GameObject 2:
    -Rigidbody with Is Kinematic DISABLED.  I want physics reactions.
    ColliderGameObject:
        -Capsule collider with Is Trigger DISABLED.  I want physics reactions.
        -Script
    AnotherColliderGameObject:
        -Box Collider
        (This is mentioned to demonstrate to you that this is a compound physics object.)
        (No script desired.)

GameObject 3:
    GameObjectContainer:
        ModelGameObject:
            ModelGameObject:
                -Box Collider with Is Trigger DISABLED.  I'm not doing anything with triggers.
                -Script
            Another ModelGameObject:
                -Box Collider with Is Trigger DISABLED.  I'm not doing anything with triggers.
                -Script
            A bunch more ModelGameObjects with box colliders but without scripts.

GameObject 1 → GameObject 2 = FAIL. No collision detected. Why!?

GameObject 1 → GameObject 3 = SUCCESS. Collision detected, even though there is only one rigidbody between the two objects, and it isn’t even on the one with the script!

The difference is that GameObject 2 has a rigidbody where as GameObject 3 does not. If I were a betting man, I would have presumed 1 → 2 would have worked over 1 → 3. Hence why I need a second pair of eyes.

Nothing fancy with the script either:

void OnCollisionEnter(Collision collision)
{
    Debug.Log("hit it!");
}

Riddle me that, Batman. Thanks.

(Googling is just leading me to a bunch of cases of people not knowing how to use Unity’s physics system. This is some fringe case and I’ve been looking at the same situation for too long.)

[tanoshimi]

“Collision events are only sent if one of the colliders also has a non-kinematic rigidbody attached.” (Unity - Scripting API: Rigidbody.OnCollisionEnter(Collision)). So that’s the second mystery solved: only one object needs a rigidbody attached, and the collision event is sent to both objects involved in the collision. If either implements OnCollisionEnter then they can act upon it.

As for the first mystery, if I understand your hierarchy correctly, you need to move the script onto the parent object:

GameObject 2:
  -Rigidbody with Is Kinematic DISABLED. I want physics reactions.
  -Script

  ColliderGameObject:
    -Capsule collider with Is Trigger DISABLED. I want physics reactions.

  etc.