# Rigid body objects passing through each other

I am experimenting with rigid body physics using the game engine for a project.

This is the setup:

• I have 2 long rectangular prisms with hole.
• The 2 prisms are connected with a cylinder (acting as a dowel).
• I locked translation and rotation for one of the prism and everything else is free to move and/or rotate.

And here's the problem:

The dowel and the free prism are going through the locked prism. Can someone please tell me what am I doing wrong? Thanks.

Here is the blend file: https://www.dropbox.com/s/o2y0pxk7ijk12bc/untitled.blend

• @CoDEmanX Thank you. I should have done that in the very beginning :) Feb 7, 2014 at 17:39
• I think its something about the Collision bounds, the rectangular prisms are actually convex, which is not suitable to be set as Box. Feb 7, 2014 at 17:42
• @LeonCheung That didn't work. I changed the prisms to convex hull and experimented with the margins but neither solved the issue. The dowel and prism still go through the other prism. Feb 7, 2014 at 17:56
• @LeonCheung There isn't a concave setting. All I have is capsule, box, sphere, cylinder, cone, convex hull and triangular mesh. Feb 7, 2014 at 18:05
• Sorry for typo, I mean they are CONCAVE. :P You may consider using the compound in Collision setting. Or try Triangle Mesh. And be sure to apply their scale. Feb 7, 2014 at 18:11

There are several problems in this file:

1. Objects scale hasn't been applied;
2. Setting Triangle Mesh here is required, since the prisms have holes, which means they are concave objects, so other collision types don't work well with them;
3. Bound margin should be tweaked carefully, as well. Considering the distance between the surface, try smaller value;
4. The two prisms stay too close to each other, which will cause "intersection" if bound margin is non-zero.

Demo file_v3. Just FYI.

Added a demo video for better understanding.

• That was magic. So the above 4 points you pointed out were the only problems? Or was there other issues? Feb 7, 2014 at 18:53
• Basically true. However, as you see in the demo file, I locked some rotation and translation axis for a better result. That's the other nice thing to do in your case, but that's not the key here. Feb 8, 2014 at 0:05
• Ridgid Body simulation has a lot of issues with concave shapes. Sergey Reich works on a special "concave" type, but no schedule unfortunately. Feb 8, 2014 at 0:29