Hi everyone,

I'm working on some RBD effects for a final year Uni course and have run into some problems that I was hoping you all could help with?

Basically I am trying to create a wall panel with a spherical cut out that will have a magnet force applied to it in order to make it look as if the panel is exploding outwards. I have the magnet force working in my scenes but the problems lie with the behavior of the object once it becomes active.

Basically, when using the bullet solver, the spherical cut out wants to “pop” out of the wall on its activation frame before it begins to shatter. Sometimes it only pops out by a unit or two that isn't noticeable when played at real-time. But other times it does a full on 45 degree rotation which is very noticeable. It seems that this problem doesn't exist with the RBD solver, just with bullet. But I'm fairly certain problem exists between keyboard and chair, not Houdini . wink

Ive uploaded a quick scene with it doing its usual thing, I have noticed in other scenes, if I were to copy my SOP Geo and translate it either in geometry level, scene level or with a null, the degree in which it all goes horribly horribly wrong changes. (The exact same wall panel translated +10 in the x will behave differently?) This boggles my mind.

Any help would be much appreciated,

Thanks in advance
S )

I've only been working with this stuff for a couple months now but from my experience you're best off using RBD solver for this sort of thing. I think with the way you have a complex static object shape with “WallOuter”, you're going to have trouble with physics data on the object. Lots of convex shapes, etc)

The other reason you'll want to use the RBD solver is that I'm pretty sure that Bullet ignores magnet forces to break glue bonds. If you are ‘seeing it working’ with magnets, most likely what is happening is the bonds are breaking from the Bullet solver's split impulse parameter, which seems to pop things out and THEN the magnet is pushing the objects around.

Again, not the most knowledgeable, someone else might have more insight here.

Thanks for your reply )

Indeed, I think I will have to have a play with RBD to see if I can get the results I am after. I have been using a combination of color and attribute transfer nodes to “unglue” the pieces when I want them to be affected by a magnet force, or keyframing the activation on and off with OBJ Position nodes.

New to Houdini since Bullet came out so didn't think of using the RBD solver straight away.

Thanks again

turning off “convex polygons” can often help but i have yet to find a good way to completely get rid of the popping, activating the object right when its breaking and using glue constraints can help