where did "scaled_pos_joint_traj_controller/command" topic defined?

[LEESHOHYUN]

when I saw rqt_graph, with roslaunch ur hardware driver ~ and rosrun rqt_controller ~, I can see /scaled_pos_joint_controller/command topic, but I cannot find where it defined. and also cannot understand, from {topic_a}/{topic b} architecture, how 'topic b' is added. may I ask where to find, and how to add topic after / ??

[fmauch]

I am not sure whether I understand your question correctly. But if you want to understand where the subscription to the topic comes from, you'll have to dig into ros_control a bit. The scaled JTC is a modified joint_trajectory_controller, so you'll find its action server there:

https://github.com/ros-controls/ros_controllers/blob/noetic-devel/joint_trajectory_controller/include/joint_trajectory_controller/joint_trajectory_controller_impl.h#L296-L299

(or, since you asked for the command topic, see this line.)

Inside this repository the controller is defined in the controllers.yaml file:

https://github.com/UniversalRobots/Universal_Robots_ROS_Driver/blob/master/ur_robot_driver/config/ur5e_controllers.yaml#L32-L46

As it is named scaled_pos_joint_traj_controller, ros_control generates a node handle using the controller name and adds the command topic inside this namespace, hence the /scaled_pos_joint_controller/command topic.

I hope, this answers your question, if not please try to specify your question a bit more.

[LEESHOHYUN]

It's a perfect answer for my question. I appreciate your help so much!