OnCollisionStay, OnCollisionEnter fires for every child collider. Is it normal?

Unity Engine
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1

So, I have an empty object “top” with Rigid body on it. It contains three child objects with sphere colliders (no rigid bodyes on them).

On the “top” object I put a script with OnCollisionStay and OnCollisionEnter implementation.

Whenever object collides with a floor (with all three colliders) the OnCollisionEnter (and OnCollisionStay per frame) fires three times (one firing for each object with sphere collider).

I expected, since I have only one Rigid body on the top of the hierarchy of colliders, there will be only one OnCollisionStay for this Rigid body. I don’t know why I expect this. Maybe some where in the past it works like this?

I found this article: Best Practices For Rigid Bodies in Unity – Digital Opus

and here there also said: “… If the cube, ball and cylinder were all grouped in the hierarchy under a single rigid body then there would be one OnCollisionStay call…”

Do I miss some changes in collisions behavior logic in Unity some time ago?
Is there any elegant way to filter all unwanted OnCollisionEnter (OnCollisionStay, OnCollisionExit) calls and stay with only one call for the rigid body on the top of the hierarchy?

2

I’m a total noob, so i can’t give detailed info or anything, but i have this same issue so it seems to be a normal thing, i had to make sure all of my spaceships have 1 Collider otherwise they trigger other ColliderTriggers 3 times if i have 3 colliders on the spaceship.

3

For any collider/collider contact, a call is made to each of the GameObjects the Colliders are on AND the GameObject the Rigidbody they are attached to but only if the Rigidbody is NOT on the same GameObject.

At best you get two callbacks, one for each collider where the Rigidbody are both on the same GameObject and four if they are not. Any that don’t have a Rigidbody obviously won’t get a separate callback.

You cannot expect a call to be made to each collider and only once on the Rigidbody (for all colliders) because that wouldn’t make sense mainly because the callback provides information on which collider is in contact.