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Hi, I'm experiementing a bit with bullet and fracturing and did some simple tests. If I know it correctly then the simulation base unit in Houdini is meter, so 1 unit (e.g. a basic polybox) is 1 meter large. If I now try to simulate real geometry like a bottle or a cup of tea, then my geometry is maybe only 0.3 units large for a bottle. These are my results: First, the real size, 0.3 units large, no substeps, convex collision geo: bullet_01_convex.mov As we can see, the collisions are quite inaccurate and the simulation is jittering a lot. That's simply because the collsion geo is inaccurate. So I switched to concave and tried again. bullet_01.mov That's more accurate but still jittering a lot. So I switched back to convex and modified the collision padding to get a better representation. bullet_01_convex_collpad.mov Collision is better, but we still have a lot of movement in the geometry. So maybe it helps to increase substeps? I increased them to 10 on the dop node. bullet_01_convex_collpad_sub.mov As you can see that was not such a good idea, the parts are jumping around like crazy. So Now I started with an increased scaling of the geometry and increasing the gravity at the same time twice, once with convex once with concave. bullet_02_concave.mov bullet_02_convex.mov Now the convex sim starts to look better. Just for testing, I increased the scaling up to 3 and did it again: bullet_03_concave.mov bullet_03_convex.mov Looks very much better. Now I tried with my real geometry: bullet_04_concave.mov still some jittering, and not enough bounce, so I increased the bounce. bullet_04_convex_bounce.mov And a bit more bouncing. bullet_04_convex_bounceHi.mov Now it looks more the way I want it. So my final conclusion is: Even if it may be physically correct to simulate a 30 cm bottle in real size, the only way to make it work as expected is to scale it up several times, simulate and scale it back down. Is this correct and can anyone confirm this? Maybe I'm completly wrong and simply missed some of the many settings in Houdini so I attached my scene. Here the uniform scaling of "transform6" node in the "alembic" network is connected to gravity to make it automatically higher if the geometry grows and bounce of groudplane and geo is higher than default. Scene file: bottle.zip bullet_01_convex_hull.mov
