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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.
Note
The commands below are given for a local installation of this repository and its dependencies as well as for running them from a docker container. For more information on the docker usage see Using Docker.
Tutorial steps
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 becausejoint_state_publisher_gui
node need some time to start. Thejoint_state_publisher_gui
provides a GUI to generate a random configuration for rrbot. It is immediately displayed in RViz.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.
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.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.
If you get output from above you can send commands to Forward Command Controller, either:
Manually using ROS 2 CLI interface.
when using
forward_position_controller
controllerros2 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
controllerros2 topic pub /forward_acceleration_controller/commands std_msgs/msg/Float64MultiArray "data: - 10 - 10"
Or you can start a demo node which sends two goals every 5 seconds in a loop when using
forward_position_controller
controllerros2 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.
[ros2_control_node-1] [INFO] [1728857332.160329225] [controller_manager.resource_manager.hardware_component.system.RRBotSystemMultiInterface]: Writing commands: [ros2_control_node-1] command pos: 0.00, vel: 5.00, acc: 0.00 for joint 0, control lvl: 2 [ros2_control_node-1] command pos: 0.00, vel: 5.00, acc: 0.00 for joint 1, control lvl: 2 [ros2_control_node-1] [INFO] [1728857332.320242591] [controller_manager.resource_manager.hardware_component.system.RRBotSystemMultiInterface]: Reading states: [ros2_control_node-1] pos: 0.67, vel: 5.00, acc: 0.00 for joint 0 [ros2_control_node-1] pos: 0.67, vel: 5.00, acc: 0.00 for joint 1
Now you can also switch controllers during runtime, which also changes the command mode automatically. First, you have to load the new controller, for example the
forward_position_controller
if you haven’t changed the launch file argument.
ros2 control load_controller forward_position_controller $(ros2 pkg prefix ros2_control_demo_example_3 --share)/config/rrbot_multi_interface_forward_controllers.yaml ros2 control set_controller_state forward_position_controller inactiveThen you can switch controllers using the following command:
ros2 control switch_controllers --deactivate forward_velocity_controller --activate forward_position_controllerObserve the output of the following CLI commands, and see how the command interfaces are claimed by the new controller.
ros2 control list_controllers ros2 control list_hardware_interfacesTry now to send commands to the new controller, as described in the previous step.
To demonstrate illegal controller configuration, use one of the following launch file arguments:
robot_controller:=forward_illegal1_controller
orrobot_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 claimedcommand 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 loadedjoint_state_broadcaster[joint_state_broadcaster/JointStateBroadcaster] active forward_illegal1_controller[forward_command_controller/ForwardCommandController] inactive
Files used for this demos
Launch file: rrbot_system_multi_interface.launch.py
Controllers yaml: rrbot_multi_interface_forward_controllers.yaml
URDF: rrbot_system_multi_interface.urdf.xacro
Description: rrbot_description.urdf.xacro
ros2_control
URDF tag: rrbot_system_multi_interface.ros2_control.xacro
RViz configuration: rrbot.rviz
Hardware interface plugin: rrbot_system_multi_interface.cpp
Controllers from this demo
Joint State Broadcaster
(ros2_controllers repository): docForward Command Controller
(ros2_controllers repository): doc