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Is PR2 also follow DH Convention?

asked 2014-11-04 02:50:25 -0500

sam gravatar image

updated 2014-11-22 17:05:54 -0500

ngrennan gravatar image

I found weird things.

I open rviz for PR2.

image description

We can see that in /base_link, z axis is blue.

But why left arm joint axis is not blue but green?

Is PR2 follow DH convention?

If not, how to understand the coordinate design of PR2?

Thank you~

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2 Answers

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answered 2014-11-09 21:51:02 -0500

fergs gravatar image

Robots using URDF rarely follow DH conventions -- and a number or ROS packages (calibration, for sure) don't necessarily work with all the extra fixed rotations that are needed to make URDF follow DH.

For the PR2, and a number of other robots, the convention has been that "when the joints are at their 0.0 position, all of the TF frames will line up parallel to the base_link orientation". Thus, if you put the PR2 arm out forward and level with the ground, with all the roll joints zeroed, all the links will be red (X) forward, blue (Z) up.

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answered 2014-11-04 06:28:16 -0500

dornhege gravatar image

The URDF allows you to freely set the axis of rotation for a joint.

The coordinate frames are probably layout so that coordinates on a link are as intuitive as possible.

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Asked: 2014-11-04 02:50:25 -0500

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Last updated: Nov 09 '14