Hey guys. Lets say I create a sphere. Subdivide the surface a few times and Cell Fracture it. After it gets Cell Fractured, I go to the Game Engine and press P to start the animation. As expected, the shards of the sphere fall. But for some reason, before the shards fall, they push each other away like an inch. I have little experience with the Game Engine but I know that there is some way to fix this. Solutions?
It sounds like your problem is that each part of the fractured sphere has a its collision set to Convex Hull. Convex hull does not perfectly math the shape of the mesh (it usually makes the collision bounds slightly bigger than the mesh), so the game engine sees colliding objects and pushes them apart which is your problem.
Sorry but I am not really sure how to fix your problem. Hopefully knowing why it happens can help you to figure it out. If you are only doing a simulation for an animation you should use the viewport physics instead because it will work much better.
Go to the tab collision bounds and modify the value margin to 0.00. this will keep the shards together until there is a collision, without that separation of initial appearance of shards.
That seemed to do it! Thank you so much. This problem has been irritating me for the past 10 months (and now I feel embarrassed from the fix being so simple…).
EDIT: Now I have another problem. Turning down the margin value to zero makes some of the shards slightly melt into the plane they fall onto. I turned all of the physics resolutions, steps, and sub steps to their highest to fix this and… nothing. This is why I like the Blender Render rigid body setup. Its easier to control what everything does.
Thecoolman5
If you are in the World of the properties tab in bullet physics / physics steps and increase the value of substeps. I think “3” solve your problem.
EDIT: Ok! Steps and substeps should be solving the problem, for me it has worked well. Try selecting these shards that go through the plan and see if your settings are the same as others. It seems that this has to do with the size of the shards. The lower pass through the plane. Then select only these shards and increase the margin of a little bump a bit. It is a bit tricky but it should solve the problem.
That didn’t do it. All of the settings on the shards are the exact same. I increased the margin on the shard that was going through the plane the most and still nothing. Ill post my blend file as soon as I can.