Physics Simulation Forum

I'm having a problem when using the bulletsharp port/wrapper.
I have three cylinders, I want the top one(dynamic) to rest on the other two(static). My setup looks like this:


For some reason, after jittering a bit, the top cylinder bounces off of the other two and falls out of view.

Here's my code to set up the scene.

//now figure out bulletsharp stuff...
CollisionConfiguration collConfig = new DefaultCollisionConfiguration();
Dispatcher collDispatch = new CollisionDispatcher(collConfig);

BroadphaseInterface broadphase = new DbvtBroadphase();
ConstraintSolver sol = new SequentialImpulseConstraintSolver();
world = new DiscreteDynamicsWorld(collDispatch, broadphase, sol, collConfig);

world.Gravity = new Vector3(0.0f, -10.0f, 0.0f);

//log (moving object)
MotionState still = new DefaultMotionState();
CylinderShape shape = new CylinderShapeZ(0.5f, 1.0f, 1.0f);
still.WorldTransform = Matrix.Translation(0.0f, 0.4f, 0.0f);
RigidBodyConstructionInfo constructInfo = new RigidBodyConstructionInfo(1.0f, still, shape);
logBody = new RigidBody(constructInfo);
logBody.SetDamping(0.04f, 0.1f);
world.AddRigidBody(logBody);

//rollers (static objects)
CylinderShape r1s = new CylinderShapeZ(0.1f, 1.0f, 1.0f);
MotionState r1m = new DefaultMotionState();
r1m.WorldTransform = Matrix.Translation(-0.2f, -0.4f, 0.0f);
RigidBodyConstructionInfo r1ci = new RigidBodyConstructionInfo(0.0f, r1m, r1s);
r1 = new RigidBody(r1ci);
world.AddRigidBody(r1);

CylinderShape r2s = new CylinderShapeZ(0.1f, 1.0f, 1.0f);
MotionState r2m = new DefaultMotionState();
r2m.WorldTransform = Matrix.Translation(0.2f, -0.4f, 0.0f);
RigidBodyConstructionInfo r2ci = new RigidBodyConstructionInfo(0.0f, r2m, r2s);
r2 = new RigidBody(r2ci);
world.AddRigidBody(r2);

And every frame is updated using:

world.StepSimulation(0.05f, 100, 0.0005f);

While debugging, the Restitution for all three objects is listed as 0.0f.
Is there anything I might be missing?

I can also mention that I have put together a similar setup in Blender using the Bullet physics there, and there is no jitter.

You need to calculate the inertia as well:

And for the static objects:

Vector3.Zero is actually the default inertia parameter value, so it's not really needed, but there's currently a bug in BulletSharp where the default value isn't passed correctly. I'll fix that soon, but for now you need to pass the zero vector.