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Example 3: Robots with multiple interfaces

The example shows how to implement multi-interface robot hardware taking care about interfaces used.

For example_3, the hardware interface plugin is implemented having multiple interfaces.

  • The communication is done using proprietary API to communicate with the robot control box.
  • Data for all joints is exchanged at once.
  • Examples: KUKA FRI, ABB Yumi, Schunk LWA4p, etc.

Two illegal controllers demonstrate how hardware interface declines faulty claims to access joint command interfaces.

Tutorial steps

  1. To check that RRBot descriptions are working properly use following launch commands

    ros2 launch ros2_control_demo_example_3 view_robot.launch.py

    Note

    Getting the following output in terminal is OK: Warning: Invalid frame ID "odom" passed to canTransform argument target_frame - frame does not exist. This happens because joint_state_publisher_gui node need some time to start. The joint_state_publisher_gui provides a GUI to generate a random configuration for rrbot. It is immediately displayed in RViz.

  2. To start RRBot example open a terminal, source your ROS2-workspace and execute its launch file with

    ros2 launch ros2_control_demo_example_3 rrbot_system_multi_interface.launch.py

    Useful launch-file options:

    robot_controller:=forward_position_controller

    starts demo and spawns position controller. Robot can be then controlled using forward_position_controller as described below.

    robot_controller:=forward_acceleration_controller

    starts demo and spawns acceleration controller. Robot can be then controlled using forward_acceleration_controller as described below.

    The launch file loads and starts the robot hardware, controllers and opens RViz. In starting terminal you will see a lot of output from the hardware implementation showing its internal states. This is only of exemplary purposes and should be avoided as much as possible in a hardware interface implementation.

    If you can see two orange and one yellow rectangle in in RViz everything has started properly. Still, to be sure, let's introspect the control system before moving RRBot.

  3. Check if the hardware interface loaded properly, by opening another terminal and executing

    ros2 control list_hardware_interfaces
    command interfaces
    joint1/acceleration [available] [unclaimed]
    joint1/position [available] [unclaimed]
    joint1/velocity [available] [claimed]
    joint2/acceleration [available] [unclaimed]
    joint2/position [available] [unclaimed]
    joint2/velocity [available] [claimed]
state interfaces
    joint1/acceleration
    joint1/position
    joint1/velocity
    joint2/acceleration
    joint2/position
    joint2/velocity

    Marker [claimed] by command interfaces means that a controller has access to command RRBot.

  4. Check which controllers are running

    ros2 control list_controllers

    gives

    joint_state_broadcaster[joint_state_broadcaster/JointStateBroadcaster] active
forward_velocity_controller[velocity_controllers/JointGroupVelocityController] active

    Check how this output changes if you use the different launch file arguments described above.

  5. If you get output from above you can send commands to Forward Command Controller, either:

    1. Manually using ROS 2 CLI interface.

      • when using forward_position_controller controller

        ros2 topic pub /forward_position_controller/commands std_msgs/msg/Float64MultiArray "data:
- 0.5
- 0.5"

      • when using forward_velocity_controller controller (default)

        ros2 topic pub /forward_velocity_controller/commands std_msgs/msg/Float64MultiArray "data:
- 5
- 5"

      • when using forward_acceleration_controller controller

        ros2 topic pub /forward_acceleration_controller/commands std_msgs/msg/Float64MultiArray "data:
- 10
- 10"

    2. Or you can start a demo node which sends two goals every 5 seconds in a loop when using forward_position_controller controller

      ros2 launch ros2_control_demo_example_3 test_forward_position_controller.launch.py

    You should now see orange and yellow blocks moving in RViz. Also, you should see changing states in the terminal where launch file is started, e.g.

    [RRBotSystemMultiInterfaceHardware]: Got the commands pos: 0.78500, vel: 0.00000, acc: 0.00000 for joint 0, control_lvl:1
[RRBotSystemMultiInterfaceHardware]: Got the commands pos: 0.78500, vel: 0.00000, acc: 0.00000 for joint 1, control_lvl:1
[RRBotSystemMultiInterfaceHardware]: Got pos: 0.78500, vel: 0.00000, acc: 0.00000 for joint 0!
[RRBotSystemMultiInterfaceHardware]: Got pos: 0.78500, vel: 0.00000, acc: 0.00000 for joint 1!

  6. To demonstrate illegal controller configuration, use one of the following launch file arguments:

    • robot_controller:=forward_illegal1_controller or
    • robot_controller:=forward_illegal2_controller

    You will see the following error messages, because the hardware interface enforces all joints having the same command interface

    [ros2_control_node-1] [ERROR] [1676209982.531163501] [resource_manager]: Component 'RRBotSystemMultiInterface' did not accept new command resource combination:
[ros2_control_node-1]  Start interfaces:
[ros2_control_node-1] [
[ros2_control_node-1]   joint1/position
[ros2_control_node-1] ]
[ros2_control_node-1] Stop interfaces:
[ros2_control_node-1] [
[ros2_control_node-1] ]
[ros2_control_node-1]
[ros2_control_node-1] [ERROR] [1676209982.531223835] [controller_manager]: Could not switch controllers since prepare command mode switch was rejected.
[spawner-4] [ERROR] [1676209982.531717376] [spawner_forward_illegal1_controller]: Failed to activate controller

    Running ros2 control list_hardware_interfaces shows that no interface is claimed

    command interfaces
      joint1/acceleration [available] [unclaimed]
      joint1/position [available] [unclaimed]
      joint1/velocity [available] [unclaimed]
      joint2/acceleration [available] [unclaimed]
      joint2/position [available] [unclaimed]
      joint2/velocity [available] [unclaimed]
state interfaces
      joint1/acceleration
      joint1/position
      joint1/velocity
      joint2/acceleration
      joint2/position
      joint2/velocity

    and ros2 control list_controllers indicates that the illegal controller was not loaded

    joint_state_broadcaster[joint_state_broadcaster/JointStateBroadcaster] active
forward_illegal1_controller[forward_command_controller/ForwardCommandController] inactive

Files used for this demos

Controllers from this demo