Lamp Made Up Of Compound Objects Likes To Stand Up In Physics Simulations

I have modelled a map in blender that I would like to simulate falling down using the physics engine inside blender. The model consists of a square base, with a square stand and a square top (squares used for simplicity to demonstrate my problem). Both the stand and the top are parented to the base. I have made each of these objects a “Rigid Body”, with the “Compound” setting checked.

The problem is that the simulation seems very unphysical to me. When I rotate the lamp to be facing towards the ground, it tries to stand upright as soon as the top hits the floor. I have attached a blend file demonstrating this.

Any suggestions as to what I am doing wrong? Looking at the physics visualizations, nothing seems to be wrong.


phystest.blend (503 KB)

Hmm. I see what you mean. The problem is that the engine is acting as though the child objects have zero mass. Unfortunately, I have no idea how to fix this. Maybe it’s a bug / something that could be fixed in Blender.

You have to use physics constraints rather than parenting to achieve “realistic” simulations, where the different parts have different masses. The problem with this is that this introduces some “slop” into the simulation.
Also, the COM (centre of mass) is at the origin of the object, not the center of geometry