Joint controller GUI failing to control arm in exercise 2.1

I’ve been trying to run the node that enables controlling the arm in exercise 2.1, however, it keeps failing as soon as I enable sending commands using the rqt_joint_trajectory_contoller gui. I would like to use this feature if it helps me learn the rest of the content. Any help would be greatly appreciated. Thanks!


  1. Launch the node using:
    rosrun rqt_joint_trajectory_controller rqt_joint_trajectory_controller
  2. Use the icon to open the graphical tools
  3. Set ‘controller manager ns’ to /controller_manager using the dropdown menu.
  4. Set ‘controller’ to arm using the dropdown
  5. Click on the power button icon to enable sending commands to the controller


The node shuts down and outputs this error message:

Traceback (most recent call last):
File “/opt/ros/kinetic/lib/python2.7/dist-packages/rqt_joint_trajectory_controller/”, line 416, in _update_cmd_cb pos = self._joint_pos[name][‘position’]KeyError: ‘position’


Sending commands to the controller is enabled

Hello @daniel.v.molina1 ,

Are you running this from the course page? I’ve just tested these steps and it’s working ok here, couldn’t reproduce your issue.


Hi Alberto I am getting the same error mentioned in this post, error

is attached here. how to solve it… I am running this from course page.

Thank you alberto, its working fine. I just refreshed the unit and its working. :slight_smile:

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