Control the UR (QUIZ): Tried Implementing on own Machine but Failed


I’m using an Ubuntu 16.04 with the UR control package cloned from github.

I’m trying to move the robot using the launch and .YAML files I created on my own for the sake of the quiz.

I first launched the “ur5.launch” file from the ur_gazebo package to bring up Gazebo with the UR model loaded.

roslaunch ur_gazebo ur5.launch

I then ran the quiz_control.launch with quiz_control.yaml loaded. However I received an error:
Controller Spawner couldn't find the expected controller_manager ROS interface

I did a rostopic list and realized the topic to publish the move commands to is /arm_controller/command and not, for egs. /ur5/shoulder_pan_joint_position_controller/command etc.

Are the gazebo models in the tutorial loaded with different definitions of the controllers and the joints? If so, can someone point me to a resource that details how I can manipulate the UR5 arm manually (publish to /arm_controller/command), and gain a better understanding of its control package?


Hi @maxxy.tjr
Try launching
roslaunch ur_gazebo ur5_joint_limited.launch
as this is what we are launching in the academy :slight_smile:

Hello @maxxy.tjr,

I cannot tell for sure how they are doing it, but if the topic is named /arm_controller/command, it’s highly probable that they are using a Joint Trajectory Controller. This type of controller allows sending commands to the whole manipulator arm instead of a single joint. You can read more about it here:

In the ROS Control Course of our academy, we are using more simple controllers (ie. the Joint Position Controller), which are loaded for each one of the joints. That’s why you are able to send commands to each joint individually.

However, in the ROS Manipulation Course, we do use this Joint Trajectory Controller in order to control manipulators. The best way to control an arm that uses this controller is with MoveIt, which you can learn how to use in the ROS Manipulation Course.

For instance, you can have a look at a practical example of what I’m talking in this video:

I hope this helps you clarify your ideas. Best,

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Ah that explains it. Thank you very much!!