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Rigid-Bodies Colliding Improperly
Confirmed, LowPublicKNOWN ISSUE

Description


System Information
Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 950M/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 436.48

Blender Version
Broken: version: 2.81 (sub 13), branch: master, commit date: 2019-10-03 21:03, hash: rBfbc096cf075b

Short description of error
Some of the Rigid-Body objects in the included .blend go flying when animation is played, as though they were intersecting each other, but they are not.

Exact steps for others to reproduce the error
Open the included .blend.
Play animation. The two objects named "Suspension.FL will go flying off in opposite directions.

Event Timeline

Investigating this problem I came across an assert on this line:
https://developer.blender.org/diffusion/B/browse/master/source/blender/blenkernel/intern/rigidbody.c$1753

For that I deleted one of the rigid body constraints and ran the animation.

It's probably not related to the bug but,
@Bastien Montagne (mont29), could you take a look at this assert first? (the assert was added in rB7f98ba47)

Fixed as rBbebdb6c82499, but this had really *nothing* to do with this report, besides being a RBW issue…

Germano Cavalcante (mano-wii) lowered the priority of this task from 90 to Low.

On further investigation, this problem has to do with how the Collision margin is calculated for cylinder shape objects.
The problem can be alleviated by reducing the collision margin of all objects involved.

Since you can work around the settings and the bullet collision code is part of an external library, I don't think it's worth investigating this.
But I will leave the decision to close the report to @Sergej Reich (sergof) who knows this area better.

As far as I know, the cylinder Collision margin box is not ticked by default, resulting in Blender assuming the value to be 0 automatically. If the box is ticked, then the value is explicitly controlled by the user. Is this the case?

On a related note, is there a specific reason 2.8x doesn't display the Rigid-Body bounding box shapes in the viewport? 2.7x did this, and it was very helpful. I'm assuming it's intentional and not a bug.

On a related note, is there a specific reason 2.8x doesn't display the Rigid-Body bounding box shapes in the viewport? 2.7x did this, and it was very helpful. I'm assuming it's intentional and not a bug.

In fact the shape drawing has been lost.
I don't know exactly what to commit, but probably in the transition to the new viewport.
Please open a new report so that the problem can be correctly addressed.

Germano Cavalcante (mano-wii) changed the subtype of this task from "Report" to "Known Issue".

I will mark it as Know Issue since this module is not in active development.
However, this problem needs to be documented.