A simple, robust setup for vellum and bullet interaction

[KarlRichter 92]

Not long ago I was tasked with a simulation of bags of hard candy falling and splitting open on the floor, with the candy of various shapes and sizes spilling out. This turned out to be way harder then I thought. There is really no built in way for vellum and bullet dynamics to interact with each other in Houdini. After searching the internet, I did find one tutorial on kind of faking the interaction, but it seemed overly complicated to me.

So after a bit of R&D I came up with this setup. Its very simple and fast, and solves both the vellum and bullet sims in one network at the same time:

It basically works by importing the RBD geo into the vellum collision solver, and the vellum geo into the bullet solver. The mass of the RBD has to be faked in somewhat, so it interacts with the cloth in a more realistic way, but that's it!

See hip for example:

vellum_x_bullet.hip

 

[nuki 39]

cool stuff!

[rookyspooky 0]

Great!

[3don 1]

Thank you for share! this is brilliant!!

[Atom 1,468]

While it's not super critical, it does seem like the collision version of the objects lag behind the actual location of the RBD objects in the simulation. I tried adding a time shift $F-1 and $F+1, but that didn't seem to fix it.

[KarlRichter 92]

Yeah, I noticed that as well. I think (guess?) it is an effect of how the DOPS black box processes sims. I messed around with the order of inputs, but either the cloth or the RBD would be a frame out of sync. It seemed to work better solving the RBD stuff after the cloth, so I left it at that. But in the end, if you grab the output of both objects at once from the DOP node, everything seems to line up with no interpenetrations. (if you check the object merge tab of the DOP node, the vellum object and bullet object are what's being exported).

 

 

 

 

Edited September 19, 2021 by KarlRichter

[zero5zc 0]

@Noobini  I'm having some problems with vellum, can you help me?

Edited April 29 by zero5zc

[zero5zc 0]

@Noobini Hello !

I`m trying to get the  interaction  between RBDfracturedobject and vellum， but the RBD pulls the cloth down, and they`re keep falling. How can  fix this?

Vellum_RBD_interaction_v0001.hip

Edited April 29 by zero5zc

[Yader 46]

Take a look at the shapematch constraint. It's suitable for rigid bodies. That way you don't have to leave vellum.

 

 

Vellum_RBD_interaction_v0001_yader.hiplc

Vellum_RBD_interaction_v0001_yader.mp4

Edited April 30 by Yader
Added video and scenefile

[zero5zc 0]

@Yader  Thank you ! This is really helpful , all in vellum !