i believe the best results i got was to make a standin, a tiny box, that would be the part the physics acted on. the actual thing that moved, i set to ignore.
group
-----thingy-ignore
-----joint
-----litlebox
i think it was, with just the joint and thingy in the group, the joints from other parts couldn't attach right or something, there'd be collisions. my complex models would be just the cylinders that touched the ground, and a bunch of little boxes that don't touch each other.