I have what I feel to be a pretty basic Rigid Body Collision question for Houdini 12.

I've got a polygonal object I created, which is basically a giant Box with a Tube-like hole going through the top and out the side of the box (think like a tunnel). I created it using a box + bent tube, then a Boolean.

I then took a Sphere, and wanted to have the sphere travel THROUGH the tunnel as it fell, so made it an RBD Object, and made the Wall/Tunnel object a Static Object. That didn't work, as the ball just stopped where the hole it was falling into was, even though it could fit. I made sure the Collision Guide Uniform Divisions was high enough so that the tunnel was properly read. It was, at 100.

I then tried the same thing but with the wall as a Terrain Object instead, still same thing - the ball just stops as if the box had no hole at all.

Am I missing something? How to get ball to fall through hole? Thanks!

Incase what I said didn't make sense, here is my problem with a screenshot:



The ball seems to stop at where the top of the box used to be, where I have cut the hole with a tube and turned it into a boolean. I imagine this is my problem, but there has to be a way to get it to read a dynamic object?

select rbd object with hole and go to > collisions > Bullet data > Polygon as convex hulls, toggle it off.
This shoul work.

or go to the Rigid Body Solver and switch it to RBD, so that it uses the collision volume your displaying in the viewport.

zdimaria
or go to the Rigid Body Solver and switch it to RBD, so that it uses the collision volume your displaying in the viewport.

This caused it to work.

Thank you very much!

Instead of making a new thread I thought I'd follow up with another similar question, this time including Fluids into my RBD simulation.

I have my ball sitting at the edge of my tube, and I have a sphere emitting a FLIP Fluid at the top of the tunnel. The fluid flows down great, and shoots out as I want it to, interacting with the ball and going around it - however, I'd like it to shoot the ball out so I can continue to animate the ball falling, etc.

I can't seem to find any specific tutorials or documentation to have the ball be affected by the fluids, rather than the fluids affected by the ball. The ball is an RBD Object, so it rolls a bit beforehand, but when the fluids hit it, it does almost nothing, they just go around it.

Is this a Mass setting somewhere, or is there a way to have my fluids “carry” my ball out with it? As well, is there a way to have my fluids emit every OTHER frame, instead of every frame (using $F) in the Creation Frame setting? And is there a way to have my Fluids be viewed as particle dots, instead of the huge fluid globs currently? Sorry 3 questions in one.

Screenshot provided as always:

Try increasing the Feedback Scale in the flip solver under Volume Motion / Solver.

Also make sure the object is a mutual affector in the merge you have.

I actually dug a little deeper and answered my own question while trying to get some objects to float; but it was indeed a Feedback Scale value in the flipsolver.

Thanks icarus!

Edit:

With regards to my other questions, does anyone know an expression, or a way to get the Creation Frame to be every other frame, instead of just every frame using $F, or just the first frame using 1? If I use ($F%2) it treats it as if it was only the value 1 still.