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Collisions inside mesh

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This is a extremely basic question so i'm sure i'm being an idiot but how do you make RBD objects (or RBD packed objects) collide with the inside of a mesh as opposed to the outside? I thought it would be as simple as enabling "invert sign" on the static container object but it doesnt seem to work!


What am I doing wrong here??


My complex scene is attached!


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Hey, thanks Jim, that works but "concave" is a lot slower to compute right? How come "inverse sign" doesn't work? Luckily it's a very simple setup so concave wouldn't add much time but I guess for bigger sims it might..


Hey eetu, that works for a single RBD object but it seems to have weird objects on a packed RBD object with multiple pieces - they all behave as one combined object.. Is there a way to fix this?



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Concave is slower, so you can make a box out of thin cubes instead, if need be.


The reason "invert sign" does not work is because that deals with a signed distance field volume for the RBD solver. You are using the Bullet Solver. There are 3 solvers to choose from in the vanilla Houdini: Bullet, ODE, and RBD. Each flavor is documented well, so check it out in the help! Bullet is the fastest but it also uses very simple collision shapes, which is a good habit. Bullet does not have an option to use volumes for collision. The closest matching primitive type in your case is "Concave".


As Eetu wrote, if you set the solver to RBD, then you can use the volume collisions and adjust the volume collision options under "RBD Solver" (as opposed to "Bullet Data" or "ODE Primitive").

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