Hi All,

I'm new to houdini. I'm trying to simulate balls bouncing on a surface. I've set up a dop network with 3 balls (platonic soccer balls) and a grid as a surface. Each piece of geometry is an rbd object. I've managed to get one of the balls to bounce on the surface but the others fall straight through. The ball that does bounce on the surface, falls through on the second bounce. The only difference btwn the balls that fall through the surface and the ball that bounces once before falling through is that they've been translated on the x axis therefore I'm inclined to believe the collision is only active in one area of the grid. Is this correct? If so, how do I increase the tolerance and why does the tolerance default to only a portion of the grid? Else, does anyone have another explanation as to why this is occurring? Thanks so much in advance. I appreciate any suggestions.

For one, it would probably help enormously to use a ground plane instead of a grid. Next, are you using the RBD solver or Bullet? If your using RBD you need to check your collision volumes and make sure you have something to collide. It sounds like your gird is making a bad volume (as it's infinitely thin). You could turn off volume based collision detection and use the edges of the grid instead, or just use a groundplane, or use bullet. Also, from your description I don't think this would matter at all, but make sure that the ball that you've transformed in x has ‘use object transform’ checked.

You could also post your hipfile so we can sort it out for sure.

zak

Thanks zak. You were right on both accounts. The groundplane is way easier but I also took a look at the collision volume issue you mentioned and was able to fix it. Balls are bouncing perfectly now. Thanks so much!