Simulating humanoid robots are not a simple task. I have been working on simulating joints and discovered that the current PhysX engine does not implement certain functions and that this will change the way we simulate joints.
Currently PhysX cannot report back how much torque is being applied to a joint, so there is know way of knowing when a joint has exceeded its maximum load. This torque information is critical when simulating a robot trying to standup or pushup when it is on the ground.
I will simulate the joint torque using a method similar to the one that I have come up with to simulate a pressure sensor. Basically I will use the Center of Mass(COM) and position of joint(fulcrum).
Once I get the formulas worked out I will post them along with some data and screenshots of one of the simulated (real) robots that I am working with.