[Question] applied_torque vs root_physx_view.get_measured_joint_efforts

[Jdowdy05]

applied_torque vs get_measured_joint_efforts vs get_measured_joint_forces

Hello, I am checking my understanding of the following three functions and what they are returning.

"Applied_torque" is the calculated torque from the actuator that does not account for any external wrenches on the actuator.

"get_measured_joint_efforts" is the external torque applied to the joints from the environment. It is essentially the "get_measured_joint_forces" wrench converted to joint space for the articulation. Im also assuming that the "get_measured_joint_efforts" is just the reaction torque and not a sum of applied_torque

I have read the documentation for both Isaac lab and Isaac sim a few times, but I am still a bit confused about "get_measured_joint_efforts," as it doesn't explicitly say you receive the reaction forces in torque like "get_measured_joint_forces" does.

Another question along the same line (though I think I know the answer): The observation function "body_incoming_wrench" has a function call inside called "get_link_incoming_joint_force". Does this give a future reaction force by some +sim.dt ahead?

Thank you in advance for the help!

[RandomOakForest]

Thank you for posting this. I'll review with the team and post here any findings.

[heleiduan]

Referring to this API doc, it seems that get_measured_joint_efforts() and get_max_efforts() from ArticulatioView cannot be accessed properly with the following errors,

torques = asset.data._root_physx_view.get_measured_joint_efforts()[:, asset_cfg.joint_ids]
AttributeError: 'ArticulationView' object has no attribute 'get_measured_joint_efforts'

While others such as get_mass_matrices() works properly.

[RandomOakForest]

Thank you for following up. I will move this to our Discussions section for the team to address.

[RandomOakForest]

Following up on this, the differences between these function is as follows:

get_applied_joint_efforts API will return a tensor that specifies the efforts set by the user through the set_joint_efforts.

get_measured_joint_forces API will return a tensor that specifies 6-dimensional spatial forces per joints for all articulations (total overall joint forces). To mimic force-torque sensors, this API can be used to retrieve forces from a fixed joint.

get_measured_joint_efforts API will return a tensor which specifies the active components (the projection of the joint forces on the motion direction) of the joint forces for all the joints and articulations.

See this doc for reference.

Let us know if you need further help.

[Zhihaibi]

Thanks for the answer, but when I use get_measured_joint_efforts(), it always returns [0, 0, 0, 0, 0, 0] when the manipulator is static. But it shouldn't be zero — there should still be torques required to counteract gravity. Is it because this function doesn't include the torques needed for gravity compensation?