# Rigid Body Constraint: how to prevent stretching

I'm trying to use Rigid Body Constraints (type=Fixed) in Blender 2.81 to connect an assembly of rigid and cloth components. a

crinoline cage

By Crinoline, 1860-1870. Jacoba de Jonge Collection in MoMu - Fashion Museum Province of Antwerp, www.momu.be / Photo by Hugo Maertens, Bruges, CC BY-SA 3.0, Link

that will move realistically (e.g. swaying when person walks). When I run the animation, the RBCs stretch infinitely, defeating my purpose. If they didn't stretch, I think the assembly would work ok, everything else seems fine. Is there a solution for this?

Update: here's a simplified example to illustrate this issue.

• Rigid Body and Cloth won’t easily interact. Can you provide your model in a .blend that others could use as a basis for providing a solution. Aug 23, 2020 at 12:54

I had no enough time to test, but it could work ... (I'm not sure how much realistic it is)

• create simple topo (lowpoly) skirt with Cloth sim
• top loop assign as vertex group for Pinning

• create rings
• manually parent each as 3point vertex

Have you come across this solution on Blender Artists: https://blenderartists.org/t/solved-how-to-combine-cloth-and-rigid-body-simulation/1194986?

eaNiiX outlines a solution that worked for him there ( in modeling a leather/metal gas mask ):

Set up the cloth sim on the desired mesh.
Create a vertex group for the areas that are attached to the solid parts and use that as a pinning group in the cloth sim.
Create an armature with a bone for every solid part.
Parent the mesh with the cloth sim to the armature with automatic weights.
Make sure the bone of every solid part has a weight of 1 influence to the neighboring vertices of the cloth mesh (same as the pinning group).
Make sure the vertices of the pinning group are only affected by the bone that controls the attached solid part. For example: Remove all influence of the left eye socket bone from the vertices of the cloth mesh around the right eye socket.
Move the armature modifier BEFORE the cloth sim.
Set up rigid body simulations for the solid parts.
In pose mode, setup “child of” bone constraints to parent the bones to the right solid parts.
Start simulation.


A simpler pinning is hopefully all you need. I suspect you've seen this answer already: Pin cloth to model

I'm not experienced with cloth simulations apart from my own attempts to do dynamic cloth pinning ( which is not really supported ).

• Thanks for this. I think eaNiiX is solving a somewhat different problem, but it may still be helpful. I shall try some experiments. Aug 26, 2020 at 19:40
• I suspect that trying to model the physics of increasing numbers of individual interacting components will quickly become cumbersome for both you and the physics solver. Have you considered using a deform mesh? I took your sample file and removed all the the physics then added a softbody cube as a deform mesh around the 'D' hoop and cloth supports and it works quite well. I don't know this would be useful for the rest of the gown - maybe one or more additional deform meshes? Again - just my 2 cents.. not a practiced modeler! Aug 29, 2020 at 7:45
• Yes, I can see that there are likely to be scaling issues with a physics approach, but I can't see how a deform mesh could handle dynamics (e.g. walking). Can you point me to an example? Aug 31, 2020 at 13:43