Rigidbody always messed up

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1

I can not get Rigidbody to work accurately

What I am trying:
A simple bangle bracelet around a wrist on an animated mesh object.

What happens:
The bangle no matter the set-up (higher substeps, weight, total friction, no bouncing) keeps bouncing around and flies through the mesh… classic!

  • Bangle is active mesh deform
  • Animated character is animated passive mesh deform deforming

Does anyone have an idea what I could do to makes something like that work?

Thank you, much appreciated.
Mike

2

  • What is the collision shape on the rigid bodies? If you have a bracelet on a character, they should both be set to “mesh’”, as they are concave shapes and they will collide with each other if they are set to “convex hull”.

  • Make sure the bracelet has it’s origin centered.

  • Also, make sure your timeline’s “playback” menu is set to “play every frame”, or else the physics preview will skip frames and break.

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3

Have you tried making a helper object?
Duplicate the relevant part of the wrist, set to non renderable, give a solidify modifier to add thickness - so the sim is less likely to ‘step’ through the mesh. Remove materials.
Use that object to interact with the bangle. It will still be animated. You can add more subdivision because it is a small object not the whole body.

Hmm - Have you tried Active, not Passive for the character? I assume using Passive means the bangle will not check to see if the wrist is moving.

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4

I was thinking about that too, but my problem was the origin being somewhere else other than the active mesh’s center.
It’s working now.

Thanks guys!

edit: awwww snap! it’s still glitching out… I just don’t get an accurate result.
when my animated mesh moves slightly fast (even though I have the triple of substeps) the bangle flies right through… and also it still bounces…
crap

sorry for being a pain, lol

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5

So try scaling body and bangle up x10. It usually makes physics work better.
One of those annoying things…
If you have imported many .obj files into blender you will have realized most 3d apps are all at a scale 100 or 1000 times bigger than blender uses. All the simulation papers that get published have for the last 20 years been based on far bigger scene sizes. Blender is doing its physics on tiny objects and the math is not working properly.

Hopefully you can either scale everything in the scene up bigger, or bake the physics of those two objects at x10, then rescale x0.1.

Oh - almost forgot. One more thing to try.
Scale up the bangle x10 in object mode. Then go into edit mode and scale it x0.1
It is the same size again, but blender thinks it is 10 times bigger & the sim comes out correctly that way. Dont apply the scale, or it goes back to failing.
You probably will need to make a Helper object like I mentioned above for the wrist, and do the same scaling trick on it.
Hope I have this the right way around… It may need to be scale up in edit mode first then down again in object…

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6

Thank you for your suggestions. It’s still behaving the same way even if I do the scaling routine… But it’s fine for now… I will get back to that at a later point :slight_smile: