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moveit_setup_assistant how to choose chain, joint and link for planning group

asked 2017-01-15 09:32:40 -0500

shawnysh gravatar image

updated 2017-01-16 00:54:02 -0500

BACKGROUND

In moveit_setup_assistant tutorial, in planning group section, it tells that click joint button to choose joints for right_arm. I did this and followed all the procedure as the tutorial tells.

However, when trying to roslaunch the demo.launch from pr2_moveit_config I generated, I found that the interactive marker was missing in rviz.

I searched for solution in ros answer and found that they said it might be either end effector or parent link of end effector undefined. I checked my config setup for pr2, however, actually all were set as the tutorial asks.

Then, I turned to the book, ros-by-example V2, CH11, which introduces moveit, where configuring planning group for pi robot, it edit chain for right_arm instead of editing joint.

So I modified chain section and deleted joint section for right_arm group for pr2.

It turned out that interactive marker appeared finally, and worked well.

QUESTION

What are meant by chain, joint and link for planning group in moveit setup, respectively?

When might one choose chain or joint for arm?

When should one choose link or/and joint for end effector?


In book, Master ROS for Robotics Programming Here is the setting for planning group, where it sets chain for arm and both joint and link for gripper( instead, the above 2 tutorial only set link for gripper). image description


In conclusion, 3 tutorials set planning group differently, why?

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answered 2017-01-16 01:35:31 -0500

rbbg gravatar image

Hi Shawnysh,

Joints, Links, Chains and Subgroups represent different ways that you can use to specify which parts of the robot (as specified in the URDF) are part of your current planning group.

Looking at the srdf wiki, you can find some more information on the different types. For instance, notice that when a joint is added, the child link is automatically also included.

A chain is just an easy way to add several joints and links to the srdf without having to manually select all the joints/links in between. It is not advisable to mix different methods in a single group.

Hope that clears things up a bit.

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It is a great explanation to my questions, thanks for your kindness,.

shawnysh gravatar imageshawnysh ( 2017-01-16 02:25:56 -0500 )edit

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Asked: 2017-01-15 09:32:40 -0500

Seen: 930 times

Last updated: Jan 16 '17