I have a question about how to understand the motor/actuator element with a joint. In particular, I am looking at the hopper environment (xml file here). The relevant part of the xml file is below: <actuator> <motor ctrllimited="true" ctrlrange="-1.0 1.0" gear="200.0" joint="thigh_joint"/> <motor ctrllimited="true" ctrlrange="-1.0 1.0" gear="200.0" joint="leg_joint"/> <motor ctrllimited="true" ctrlrange="-1.0 1.0" gear="200.0" joint="foot_joint"/> </actuator> 1) If you look at the below image there are only two joints? But the xml file displays three? 2) There are 3 degrees of freedom - one for each joint. Does the motor control the amount of force applied to the joint or the direction that the force is applied?
1) the model has 6 joints 3 hinge joints for the position of the hopper and one for each thigh-, knee-, and foot-joint. 2) the motor applies a torque at each joint. The sign of the torque determines the direction in which the torque is applied. I have never used the gear mechanism but I guess it just multiplies your inputs with the ratio. Your inputs are limited between -1 and 1. So the motor can apply torques in the range of -200 and 200.