I've implemented the accumulated impulses technique used by Erin Catto in Box2D in a small 3D physics program. Accumulating normal impulses with contact caching works great, as I can make stacks with a decent number of blocks which come to rest by themselves with no damping or sleeping. However, when I enable rotational motion, they start to slide and slip off because I haven't figured out how to do friction with accumulated impulses.
So, my question is, how do I calculate friction with contact caching and accumulated impulses in 3D? Box2D is in 2D, so its friction direction is just the normal rotated 90 degrees, as motion can only occur one way or the other in 2D. Are there any simple papers or demos which demonstrate accumulated impulses and friction in 3D, similar to the way Erin Catto's original Box2D (Box2D lite now) demonstrates it in 2D?