parented, kinematic rigidbodies moving independently when parent is nudged.

Make a physics "ground"
Make a sphere, add a rigidbody.
Make a box, add a rigidbody, change the flag to isKinematic,disable the collider (effectively making an inert physics object)

Parent the box to the sphere.

In play mode, move the sphere around with the transform gizmo, the box will wildly creep from the parent.

is this intentional?

 

Could you file a bug? Child rigidbodies should not be influenced by parent rigidbodies.

 

I was expecting the child rigidbody to be 100% influenced by the parent when isKinematic. This is a recent bug when upgrading from 2018.1.5 to 2018.2

bug is being filed.

 

It probably should be affected by the parent in that case.

 

A Rigidbody component takes over its GameObject's Transform. As for what I can tell, child rigidbodies aren't intended to be affected by their parents in any case. If that happens (child rigidbody being affect by its parent) then it's a bug.

Please check out this thread:
https://forum.unity.com/threads/wha...-my-entire-game-with-child-rigidbodies.544985

From my reply in that thread:

This explains why are you observing different behaviors among different Unity versions. The correct behavior is the child rigidbodies being independent of their parents.

 

Unity has reported that it is, in fact, a bug, and will be resolved in 2018.3. The behaviour starts in 2018.1.6. Rigidbodies should behave independently of their parents, UNLESS they are checked as IsKinematic, then they are basically inert.

 

Where is that stated? As far as I understand, a kinematic rigidbody is static in the scene independently of any parent rigidbody. Kinematic rigidbodies should be moved via MovePosition and MoveRotation in order to interact correctly with other physics elements.

 

Having the same issue with 2018.2.14f1.
Is there a workaround or something?

 

I hit this recently. Try changing the Interpolation of the child kinnematic rigidbody to None. I know it would seem that should not matter. Also I have not been able to establish if AutoSync and SyncTransform should affect kinnematic rigidbodies. It would be useful to know!