Joints to the Physics Engine are like Shaders to the Rendering Engine. They are the fundamental building blocks to construct advanced physics models for games including cars, tanks, robots, mechs, powered ragdolls, construction vehicles, monster trucks, heavy weight machinery, ropes, bridges, virtual creatures, ..., etc. The default Unity physics engine, PhysX, unfortunately works very poorly with articulated multi-rigid body models consisted of multiple joints. The joints simulated by PhysX...
APE - Articulated Physics Engine for Robust Joints and Powerful Motors
APE - Articulated Physics Engine for Robust Joints and Powerful Motors