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I have been reading the various packages that pr2 arm controls uses.

1)http://www.ros.org/wiki/pr2_mechanism_model

2)http://www.ros.org/wiki/pr2_mechanism/Tutorials/Coding%20a%20realtime%20Cartesian%20controller%20with%20KDL

3)http://ros.org/wiki/ee_cart_imped_control#

The API from the first link shows that you can get the measured force of the joint.

However, I can't find any of such members in the 2nd link(or in the KDL library). And from the 3rd link, it says that PR2 don't have force sensors on its joints.

Why do they contradict each other? Could someone clarify with me on this? Thank you in advance. :)

Also, if PR2 joints indeed cannot sense the force/torque on the joint. May I know what does "effort" mean in joint_states_listener Thanks!

EDIT: I'm running simulation on Gazebo if that makes any difference


Originally posted by ccm on ROS Answers with karma: 226 on 2013-03-14

Post score: 0

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1 Answer 1

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The stock PR2 does not have force sensors on the joints.

The effort mentioned is the estimated force based on the motor current for that joint. The motor and mechanism models are quite good, so the estimated forces are pretty good. The motor control boards are effort-based, so controller output is generally a commanded effort.

In your second link, the joint efforts are referred to as joint torques; the variable in question is tau_


Originally posted by ahendrix with karma: 47576 on 2013-03-14

This answer was ACCEPTED on the original site

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Original comments

Comment by ccm on 2013-03-15:
Thanks, that made things clearer.

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