I'm trying to use Bullet Physics in my iOS game. The engine appears to be correctly compiled in that the demos work fine.

In my game I have the player's ship and some enemy ships. They're defined as btRigidBody objects and btCollisionObjects and I'm using btSphereShapes for collision.

At 'fast' speeds, collisions appear to happen sensibly - things collide and nothing goes 'weird'. If the speeds are very slow though and the player's ship touches a non-moving object the collision happens, but then the player's ship moves at incredible speed over the next few frames and appears a long distance from where it collided - completely out of proportion to the speed it was moving before impact.

To move the things around I'm using setLinearVelocity() each frame, ticking the physics engine, then using getMotionState() to update the rendering code I have.

Part of the issue might be I don't quite understand how to set the correct mass or what the best speeds are to use for anything. I'm mostly sticking numbers in and seeing what happens.

Should I be using Bullet in this way, and are there any guidelines for deciding on the mass of objects? (am I right in assuming that in collisions heavier objects will force lighter objects to move more)