# MoveIt desired joint angles topic

Hi all,

When MoveIt computes and executes a trajectory, it does the following steps:

1. Compute the desired joints trajectories (i.e. the path)
2. Publish the desired path on topic /move_group/display_planned_path
• The desired is provided as a set of samples of desired joint angles
3. Execute this desired path
• In order to execute the path, the desired path samples are input into the joints controllers (arm_controller)

Do you know which topic is used to provide the controllers with the desired angles?

Thanks,

Antoine.

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This depends on your actual setup, but if you follow the most standard approach, you should have controllers specified as described here. You´ll thus probably want to check if controllers are set in the "config/controllers.yaml" file in your robot´s MoveIt! setup package. The standard controllers are commonly using a control_msgs/FollowJointTrajectory Action interface, so multiple topics are used for coordinated execution. One easy way of finding out what topics are actually used is doing a

rosnode info move_group


and inspecting the output, looking for trajectory related publishers. The other way is looking at the controllers.yaml file and figuring out the topic names from there (which requires consideration of namespaces in launch files etc.)

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Hi Stefan, it seems I am getting there, I believe the executed trajectory is in topic /arm_controller/follow_joint_trajectory/goal. This message contains all the trajectory points, can I assume that a desired trajectory point is sent to the controllers at each time step?

( 2014-08-13 04:04:54 -0500 )edit

Also I am not sure I understand the notion of action interface. I have looked around but could not find an explanation. I noticed they are gathered in files like FollowJointTrajectory.action though I am not sure how they are used thereafter...

( 2014-08-13 04:06:47 -0500 )edit

Ha! I think I get the action interface , it is detailed here: http://wiki.ros.org/actionlib/Detaile... . The first question on the timely basis the trajectory points are used still holds though ;)

( 2014-08-13 04:34:06 -0500 )edit