Free torque is a torque that is applied to a joint without any external load or resistance. This type of torque is used to model the behavior of a joint that is moving freely, such as an arm swinging back and forth with no external forces acting upon it. In a robot simulation, free torque may be used to test the limits of a joint's range of motion or to evaluate the performance of a control algorithm in the absence of external disturbances.
Forced torque, on the other hand, is a torque that is applied to a joint in response to an external load or disturbance. This type of torque is used to model the behavior of a joint that is interacting with its environment, such as a robot arm lifting a heavy object or pushing against an obstacle. In a robot simulation, forced torque may be used to test the ability of a robot to handle different types of loads or to evaluate the effectiveness of a control algorithm in the presence of external disturbances.