Controllers

One of the main questions of this first milestone is how to model the controllers for the biped simulation.

The neural network will output the desired angle for every joint and we hope to apply a relevant torque to each joint in order to reach that desired angle. A PD controller can be assumed to control each joint, in this case a constant value for the proportional coefficient and one for the derivative coefficient needs to be assumed. Large values can make the physics simulation unstable and these values seem to need some tweaking. Other options are to use the built in features for PhysX motor enabled joints which can make the joint move at a specific speed or to a specific angle. The torque can be limited on these motor joints which should be a very good feature.

Some more testing on the model needs to be done in order to come up with this efficient control method for each joint.

This project from Ecole Polytechnique Federale De Lausanne mentions some problems associated with joint controllers, the solution selected in the project is to use a constant speed for the joint equal to the proportional coefficient. Teta_dot = k(delta_Teta). The justification being that larger difference in desired angle from existing angle needs larger values for velocity to move the joint.