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Cloth and RBD: two-way interaction?


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I'm trying to figure out how to set up a network that would allow for a two-way interaction between cloth and RBD solvers.
Imagine a "chain" that consists of two metal objects connected with a cloth strap and another strap dangling from the second object:
The uppermost box must be animatable. Everything else should be driven by dynamics and constraints.

Looks like there's no easy way of making a cloth object affect a rigid body.
For now, I tried the following workaround. I made the lower box a cloth object and bound it with stitch cloth constraints to both cloth straps. However I can't get any good results with it. Most of the time the box just shots away like from a sling, orbits around the scene and ultimately explodes on contact with either the ground plane or the other box. Not to mention that the box behaves oddly as a cloth object (like filled with air), and even weirder with constraints attached to it.


Ideally, I'd like the upper box to be a static RBD and the lower one an RBD constrained to the upper strap. So when the static box starts to move, the cloth strap begins to drag the lower box around. Is this possible? What would be the best way to approach this problem?



Initial scene (no dynamics + ground plane): metal_leather_chain_scene.hipnc

Some tests with cloth box: metal_leather_chain_sim.hipnc

Edited by ajz
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Hello Eetu. Thank you for your reply.

I gave your scene a try and have spend some time with it, but I have one problem with this wire solution.


Around frame 70 of your scene, the upper strap stiffens at an odd angle, stopping the box from returning to its original position directly below the upper cube. I tried to tweak elasticity and plasticity of the strap, but it didn't have any effect. Then I noticed that the strength of soft constraints is the culprit (or at least I think so), because when I increased it, the box started to behave like an inflated ball, falling very slowly, or - with even bigger strength values - going up. On the other hand, with lowered strength values the box behaviour is acceptable, but constraints are much looser, and what I need is this box sticking to the end of the strap as close as possible. So, I kind of hit a dead end with wires for now, but I bet there are some clever workarounds for this.


metal_leather_chain_scene_ee2.hipnc (H13)


I'm currently experimenting with FEM and quasi-solids. It's much slower, but I find the results more reliable.

However even with this solution I have a problem. I can't find a good way of constraining two solids other than with Stitch Cloth. And this type of constraint causes deformation of both constrained objects during sim initialization.

What other type of constraint can I use to link two solid objects?


metal_leather_chain_fem3.hipnc (H14)

Simulation cache files: https://www.dropbox.com/s/11lr2yrxe5m3fz0/metal_leather_chain_fem_CACHE.7z?dl=1 (32MB)

Edited by ajz
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