Problems with rigid bodies

Hello everyone. I have a cube along with cell fractured text inside the cube. I want the text to force each other apart for a short period and then bounce around the cube before falling onto the bottom of the cube. No matter what I do, the cell fractured text reacts to the cube as being a solid object. I tried applying a solidify modifier, I played around with the normals, and the rigid body settings and nothing works. Solutions?

.blend file?

Yeah… The blend file is always welcome for simulation problems. Still… I read your post and I had a flash: Check the Collision Shape of your cube and eventually change from “Convex Hull” to “Mesh”.

Convex hulls can’t be hollow. :eyebrowlift:

All of the shards are set to Mesh. I even set the Cube to Mesh. Still nothing. Here is the blend: http://www.pasteall.org/blend/25443

This file does not match the description above. It contains no solidified cube, no shards, and no rigid bodies as far as I can tell. Try again?

Really? That is weird. I’ll re-upload the file. PS: The rigid bodies are on the second layer. http://www.pasteall.org/blend/25446

Still not the right blend file.

No cube, no rigid bodies, no shards. Just a sphere animated to go upwards through a text converted to mesh over a plane light… And nothing on the second layer or any layer other than the first one.

Same player, shoot again! :wink:

Ohhhh. That is my older version of the animation I had a go at. Now, why is PasteAll uploading that file when it no longer exists on my system? Anyway, after some digging, I found the right file: http://www.pasteall.org/blend/25456 If that isn’t it, I will upload a different one that I think might also be the correct one.

Now we have everything as advertized. :wink:

First thing: If you don’t intend to really animate the cube, just set it to Passive.

For the rest, in the “Rigid Body World” panel, set the “Steps per Second” to 120 and the “Solver Iterations” to 60.

That’s all. Your text will explode.

Thank you so much. Did setting the cube to Passive make it work? I don’t understand how it did. And I see why you set the cache settings to much lower values. Don’t want to bake the simulation all night…

Changing the cube to Passive (and not animated) was something I did instinctively when I noticed that it wasn’t really animated. (No keyframes.) And it wasn’t enough. The shards were still ejected at the speed of light. :confused:

Changing the settings of the Rigid Body World to something more reasonable did it.

I discovered in a recent project that higher values don’t always mean better. Low settings are unstable because the calculations aren’t precise enough but, on the other end, very high values can introduce some new instability because the calculations are so precise that the simulation becomes very sensitive. The rounding errors accumulate at the speed of light and the simulation turns into a new Big Bang. :smiley:

Oh okay. After setting the cube to passive and changing the cache settings, the shards did exactly what I wanted them too but it wasn’t enough. I then went straight to reset the cache values to their highest and the simulation did even more exactly what I wanted them to. But, just like you said, higher values can give too much accuracy. I had to animate the Sensitivity Margin to make it better. Anyways, thanks guys!

Something that I forgot: I also gave some “realistic” mass to the shards with the “Calculate Mass” button in the Tools shelf. IMHO, shards always behave more realistically than with the default mass given by the Cell Fracture tool.