RBD issue: How can I bring them to stop?

[Masoud]

Hello guys,

In a simple RBD simulation, when I replace the "Ground Plane" collision DOP with my Collision-Box, the rigid body objects never stop moving! How can I bring them to stop?

(When I use the "Ground Plane" node, everything is ok!). I tried to use the " rbdautofreeze DOP", but it doesn't work.

 

Thanks for helping.

RBDs_01.hip

[madebygeoff]

Are you sure your collision box is set up properly? The default setting uses a convex hull operation to simplify the incoming collision geo. Normally that will create a solid box, so your objects (which are inside the solid box) are constantly intersecting with the collision geo creating a solve that is mathmatically impossible, creating jitter. Try setting the collision type from "convex hull" to concave.

Search "Houdini RBD jitter" for endless discussions of this. There's also a good masterclass that Jeff Wagner did a while back all on collisions that is very helpful.

[Atom]

Try using a groundplane, instead of the inside of a VDB box. Set your  Sleeping Time to 0.1.

Edited January 15, 2022 by Atom

[Masoud]

Hi Atom,

I want to use my custom collision object, so why a "groundplane" works fine, but my collision doesn't?

[Atom]

As Geoff suggested, your collision surface may not be setup correctly. They're probably bouncing around due to the gaps in your vdb supplied collider. Instead, model a box with some extruded thickness and supply that, not as a vdb, but as surface polygons. VDB colliders are for pyro and flip sims.

Edited January 16, 2022 by Atom

[madebygeoff]

Really recommend Jeff Wagner's talk on RBD collisions. I switched from VDB to surface and lowered the collision padding a touch to .01. That seems to work.

 

RBDs_02.hipnc