Expose qfrc_actuator and qfrc_external on EntityData#779
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Add qfrc_actuator (actuator forces in joint space) and qfrc_external (J^T * xfrc_applied contribution recovered from the qfrc_smooth identity) as read-only properties on EntityData, sliced to entity joint DOFs. Remove generalized_force which was bugged (indexed free joint DOFs instead of articulated DOFs) and had an ambiguous name. Update joint_torques error message to point to the new accessors. Fix electrical_power_cost to use qfrc_actuator instead of actuator_force so mechanical power is correct for actuators with non-unit gear ratios. Fixes #776
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MuJoCo decomposes generalized forces into physically distinct components but
EntityDataonly exposedactuator_force(in actuation space, not joint space).This adds
qfrc_actuator(actuator forces projected into joint space through the transmission) andqfrc_external(recovers the J^T *xfrc_appliedcontribution that MuJoCo folds intoqfrc_smoothwithout storing separately). Also removesgeneralized_forcewhich was bugged (indexed free joint DOFs instead of articulated DOFs) and had an ambiguous name.Fixes
electrical_power_costto useqfrc_actuatorinstead ofactuator_forceso mechanical power is correct for actuators with non-unit gear ratios.Fixes #776