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Rigidbody Mesh Collision Instability with Simple Torus
Confirmed, NormalPublicKNOWN ISSUE


System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: Quadro 4000/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 353.30

Blender Version
Broken: version: 2.82 (sub 7), branch: master, commit date: 2020-03-12 05:06, hash: rB375c7dc4caf4
Worked: (optional)

Short description of error
I am a grad student making videos for undergrad students in lab. So, I studied blender in one day then make some videos for other lab lectures.Then I meet one problem with physical chain attach to some objects (the chain have to be a bit long.) I find out some physics in blender 2.8 not quite work. Of course, it also cloud be my mistake due to lacking knowledge of the blender settings. Here is what happened to my blender app.

I try to create a physical chain in blender, but it is not quite working. when I set all everything with rigid body then it works. However, the chain start to break when I want to add more length to it. also I find it will break when I try to make the size to the chain smaller for each segment.
Exact steps for others to reproduce the error

[Please describe the exact steps needed to reproduce the issue]

Event Timeline

Hans Goudey (HooglyBoogly) changed the task status from Needs Triage to Confirmed.EditedMay 18 2020, 11:03 PM

Thanks for the report. I tried to fiddle with the settings as recommended here, T72716#838777, but I couldn't get this to work.

I also made a simpler situation with just three simple objects where the collision fails:

I tried with multiple margin values and masses. I feel like such a simple situation should work, but I also have a hunch others might consider this a "Known Issue" based on bigger problems with the physics system.

Hans Goudey (HooglyBoogly) renamed this task from Bug for physical chain to Rigidbody Mesh Collision Instability with Simple Torus.May 18 2020, 11:05 PM
Jacques Lucke (JacquesLucke) changed the subtype of this task from "Report" to "Known Issue".May 19 2020, 2:41 PM

It does not seem like a bug to me. I was able to improve the simulation quality in both cases considerably by changing some solver settings in the Rigid Body World panel (in the scene settings), by changing the collision margin and by giving it more geometry to work with. It can probably be improved even more by tweaking the settings a bit further.

I'd only consider this a bug if this did work in older versions of Blender. Please check that.

My bad, that's just my unfamiliarity with the rigidbody system then. I didn't realize it would actually work better with more geometry.

Since the solution is just increasing the simulation quality, I would say this isn't even a known issue.

We might also have a better way of handling this when is reviewed and merged. (Just a heads up)