Unit 2 Exercise 2.7.1 - Joints are not responding

When I launched the my_robot.launch.py the first time when going through the exercise, I was able to modify joint1 of the robot. However, when I added the modifications to joint2 in the files for exercise 2.7.1 and ran the launch file again, it launched successfully but did not update the joint values. I just get this message on the terminal:

I made sure that the code I copied is similar as in the notebook. Anything I am doing wrong?

Hello @HusamArdah,

The message that you are seeing is the expected message that you get when commanding a position to the robot arm. I assume that your problem is that the robot is not moving in simulation, is this correct?

Perhaps your robot is already at the indicated position, and therefore this command does not move the robot?
Experiment with sending various different values and observe the robot’s motion:

For instance:

ros2 topic pub /forward_position_controller/commands std_msgs/msg/Float64MultiArray "data:
- 1.57
- -1.57" -1

and then:

ros2 topic pub /forward_position_controller/commands std_msgs/msg/Float64MultiArray "data:
- -1.57
- 0.79" -1

Do you see the robot move now?



Unfortunately the robot did not respond.

I also made sure that my config and launch files were the same as provided. Is there any code file I should provide you?

Hello @HusamArdah,

yes I would need to look at your code, could you please post here the contents of the rrbot.xacro file located here: ~/ros2_ws/src/ros2_control_course/unit2/rrbot_unit2/urdf. Additionally I need to have a look at your controller_configuration.yaml file, located here ~/ros2_ws/src/my_robot_bringup/config.

Also, from you title I understand that you are doing exercise 2.7.1. , but does everything explained under Section “2.6 Test your ros2_control pipeline”, work?

Thank you,


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