Question about set_external_force_and_torque() usage in IsaacLab

[strn18]

Hi,
I have a question about how set_external_force_and_torque() is intended to be used for controlling an Articulation in IsaacLab.

In my setup, I am controlling a robot hand that is not fixed to the world. Gravity is disabled, so the hand is essentially a floating articulation. When my policy outputs actions, I use part of the action vector as force and torque inputs and apply them to the hand via set_external_force_and_torque() to translate and rotate it.

I understand how joint-level control works with functions like set_joint_position_target(). In that case, if I provide a joint target value (e.g., 1.2), that value is treated as a PD controller target, and the joint is driven toward that position (1.2).

However, set_external_force_and_torque() seems to behave differently. For example, suppose I want to move the robot from position (1, 0, 0) to (3, 0, 0). If I pass (3, 0, 0) as the force input to set_external_force_and_torque(), it appears that this does not mean “move the robot to position (3, 0, 0)”, but rather “apply a constant force of magnitude (3, 0, 0)”, regardless of the current position.

This leads to my main question.

Assume that I know:

• the current position and rotation of the robot, and
• a desired target position and rotation that I want the robot to reach.

Is there a principled way to determine what force and torque values should be passed into set_external_force_and_torque() so that the robot reaches the target pose?

From what I understand, set_external_force_and_torque() stores force and torque values in a buffer, and later, when write_data_to_sim() is called, self.root_physx_view.apply_forces_and_torques_at_position() is executed. I tried reading the Omni Physics documentation for apply_forces_and_torques_at_position(), but the description was quite high-level and did not clearly explain how these forces are meant to be interpreted or designed for pose control.

So, in short:
Given the robot’s current position and rotation, is there a recommended or standard way to compute the inputs to set_external_force_and_torque() that would drive the robot toward a desired target position and rotation?

Thanks in advance, and sorry for the long question.