Spheres inside sphere

[sueshijuu]

Hello all,

I'm trying to create some RBD spheres inside a much larger RBD sphere. Imagine something like a chewing gum ball dispenser machine type thing.

I can get that to work, no problem. The little spheres are inside the big sphere and collide with the inside. Great.

But what I'd like to do with it is break the largest sphere. Make a hole in it. So the smaller spheres can escape through the hole (if I make the large sphere move).

I've created a hole with a Break sop. When I use the sphere with a hole in it, it screws up the collision detection. It used to be a perfect circle when I checked on 'show collision guide geometry'. But with the hole in it, it's just bits and pieces, scattered across the surface. The simulation goes terribly slowly, the small spheres get stuck on the bigger sphere. It's just not correct at all.

It obviously has something to do with the hole in the geometry. Maybe I'm building it in a completely wrong way. I just don't really know.

I'm quite new to Houdini. So if anyone has any advice on this topic, tips, help, whatever, I'd be very happy to read it. I tried to take some helpful screen shots. I could include a scene file.

Thanks.

[eetu]

Have you tried turning off Laser Scan?

Is your fractured sphere still airtight, i.e. are there polygons in the cut glass edge?

[asnowcappedromance]

Hi,

collision seems to work fine for me, check out the attached file.

Make sure your container sphere is not too thin, otherwise you have to up the division samples of the ray intersect quite a lot.

Also, setting surface representation to edges gives you better collision results.

anyway, go over my settings, hope that helps,

cheers,

Manu

RBD_concave_collision.hipnc

[sueshijuu]

@eetu: Turning off laser scan (in combination with making the geo thicker) helped. It helped before there was a hole in the geo. Invert sign wasn't needed either anymore.

@manu: The surface was indeed too thin, that was the (main) problem. I thought I had tried that out but it works in combination with the divisions. Thanks for the example, it's perfect. And now I understand what the cookie sop does, haha. I had been trying to do this with polyextrude, but I think cookie was actually the thing I needed to begin with.

So both of you, thanks a lot for the super quick replies!

I'll get it working fine now.

Cheers.