Solved Misbehaving rigid body particles - thinking inside the box

Well I have been working a while back on getting rigid bodies to work with particles in an animation. I have attached the file I’m working on which I render out a hundred plus frames to ping files and use in another blend in a compositor. The “box of cereal” nearly works, but the flakes protrude through the box. See attached render. It seems that the combination of particles to rigid bodies is in effect at the origin of the flake instead of the outside of the flake for collisions which allows it to protrude part way through the box. Can anyone think inside the box so the flakes stay in it? Script in blend file I used.

Tim
http://www.pasteall.org/blend/35627


Your file seems to be incomplete?

I might be the cache. Alt A and it worked on my computer. If not, I’m stumped.

No idea what went wrong, I retried and downloaded successfully.

It is not entirely clear what you are trying to do. I found an emitter plane, which does not seem to be related to your cereal box, and 1000 particles growing in your box and exploding from it? I am afraid you hit the limits of the particle system, as your particles hit the box at high speed, which makes it hard for Blender to calculate collisions. Is it an idea to just load the cereal in the box and shake it out?

Your solidify modifier on the box won’t influence the collisions. So the flakes are colliding with the OUTSIDE of the box, not the inside.

But the main issue is that your bits of cereal are moving waaaaaay too fast. In fact, I did a test by just spreading out a bunch of flakes in the box, removing any initial movement, and letting gravity take its course. It seems more realistic to me.

If you really want to keep them moving at that speed, you should increase the number of “Steps Per Second” in the Rigid Body Cache options (where you bake the simulation). Your flakes are moving so fast that they move past the boundary of the box before the solver can calculate the collision. Fast movement requires more frequent calculations, otherwise things go awry really fast.

I managed to fix the problem. I believe you used the particle to rigid bodies add-on . Instead I started over by having the flakes fall in the box first. I then paused the simulation and I joined the flakes. I parented the joined flakes to the box and keyframed the animated checkbox in the rigid bodies so it activates right when the box rotates. Separated by loose parts, set the origin to geometry and that’s it. The flakes follow the box and activate right when it rotates.
Here’s the .blend: http://www.pasteall.org/blend/35635

Oh my gosh. Thanks so much. I never would of thought of that. I owe you big time now. Thank you.

Tim

No problem.

Benu. Good explanation. Now I know why the little devils wouldn’t stay in the box. I didn’t know solidify had no effect. That helps a lot. I can use that information on some other things I’m working on.