strange penetration behavior

[markbaker]

I have a world with a btSphereShape (ball) that I control colliding with a static btConcaveShape-derived shape (a flat plane with a cube sitting in the middle) extended for per-triangle collision. Restitution & Friction in the collision callback are both set to 0.

When my ball collides with the triangles on both the north & west facing sides of the cube, the collision behavior works fine. I can rest the ball up against these sides to a standstill. The penetration is perfect.

However, for the south and east sides of the cube, there's a slight penetration & a bounce. It's impossible to rest the ball up against these two sides, as they keep repelling the ball.

I tried reversing the winding order of the triangles, still the same behavior. Any idea how to fix this?

[Erwin Coumans]

The problem might be in your custom collision shape. Have you considered just using a btCompoundShape with a btStaticPlaneShape and btBoxShape as child shapes?

If you can reproduce the problem in a Bullet demo, someone might be able to help out.
Thanks,
Erwin

[markbaker]

i believe it may be because my ball mesh's size isn't the same as the sphere shape's radius

How do I match the radius value in 3D studio max to the sphere shape?