How to get robot_description from the /robot_description topic in the launch file？

Question

i have implement that firstly start the hardware driver in the controller(Linux robot 5.15.113-rt64 #2 SMP PREEMPT_RT), the PC to open the Moveit service, and then use the Moveit programming to achieve the control of the robot in PC.

i start the hardware driver，the nodes are as fellowing:

robot@robot:~/Desktop$ ros2 node list
/body_controller
/controller_manager
/head_controller
/hyy_external_device_controller
/joint_state_broadcaster
/left_arm_controller
/right_arm_controller
/robot_state_publisher

and then i start the moveit2 services, here is the launch file：

def generate_launch_description():
    # Declare arguments
    declared_arguments = []
    declared_arguments.append( 
        DeclareLaunchArgument(
            'if_add_axisgroups', 
            default_value='true', 
            description='if true, then add axis groups'
        )
    )
    declared_arguments.append( 
        DeclareLaunchArgument(
            'if_add_external_device', 
            default_value='true', 
            description='if true, then add external devices'
        )
    )
    declared_arguments.append( 
        DeclareLaunchArgument(
            'ifstartRviz', 
            default_value='false', 
            description='if true then start Rviz'
        )
    )

    # Initialize Arguments
    if_add_axisgroups = LaunchConfiguration('if_add_axisgroups')
    if_add_external_device = LaunchConfiguration('if_add_external_device')
    ifstartRviz = LaunchConfiguration('ifstartRviz')
    
    # Get robot_description(URDF) via xacro
    robot_description_content = Command(
        [
            PathJoinSubstitution([FindExecutable(name = "xacro")]),
            " ",
            PathJoinSubstitution(
                [FindPackageShare("h1_description"), "urdf", "h1.xacro"]
            ),
            ' if_add_axisgroups:=', if_add_axisgroups,
            ' if_add_external_device:=', if_add_external_device,
        ]
    )
    robot_description = {"robot_description": robot_description_content}
    
    yaml_file_path = os.path.join(get_package_share_directory('h1_robot_moveit_config'), 'config', 'moveit_controllers.yaml')
    moveit_config = (
        MoveItConfigsBuilder("h1_robot")
        .trajectory_execution(file_path=yaml_file_path)
        .to_moveit_configs()
    )

    planning_scene_monitor_parameters = {
        "publish_planning_scene": True,
        "publish_geometry_updates": True,
        "publish_state_updates": True,
        "publish_transforms_updates": True,
    }

    # Start the actual move_group node/action server
    run_move_group_node = Node(
        package="moveit_ros_move_group",
        executable="move_group",
        output="both",
        parameters=[moveit_config.to_dict(),
                    planning_scene_monitor_parameters,
                    robot_description,
        ],
    )

    # RViz
    rviz_config_file = os.path.join(get_package_share_directory("h1_robot_moveit_config"), 'config', "moveit.rviz")
    rviz_node = Node(
        package="rviz2",
        executable="rviz2",
        name="rviz2555",
        output="both",
        arguments=["-d", rviz_config_file],
        parameters=[moveit_config.to_dict(),
                    robot_description,
        ], 
    )

    # Static TF
    static_tf = Node(
        package="tf2_ros",
        executable="static_transform_publisher",
        name="static_transform_publisher",
        output="both",
        arguments=["0.0", "0.0", "0.0", "0.0", "0.0", "0.0", "world", "fake_link"],
        parameters=[],
    )
    
    delay_rviz_node_after_run_move_group_node = RegisterEventHandler(
        event_handler=OnProcessStart(
            target_action=run_move_group_node,  # Ensure the last controller loaded triggers this event
            on_start=[
                TimerAction(
                    period=5.0,
                    actions=[rviz_node]  # Wrap the Node in a list
                )
            ]
        ),
        condition = IfCondition(ifstartRviz)
    )

    return LaunchDescription(
        declared_arguments +
        [
            static_tf,
            run_move_group_node,
            delay_rviz_node_after_run_move_group_node
        ]
    )

and everything is working fine, then i start the task node(program with moveit api), here is the launch file:

def generate_launch_description():
    # Declare arguments
    declared_arguments = []
    declared_arguments.append( 
        DeclareLaunchArgument(
            'if_add_axisgroups', 
            default_value='true', 
            description='if true, then add axis groups'
        )
    )
    declared_arguments.append( 
        DeclareLaunchArgument(
            'if_add_external_device', 
            default_value='true', 
            description='if true, then add external devices'
        )
    )

    # Initialize Arguments
    if_add_axisgroups = LaunchConfiguration('if_add_axisgroups')
    if_add_external_device = LaunchConfiguration('if_add_external_device')
    
    # Get robot_description(URDF) via xacro
    robot_description_content = Command(
        [
            PathJoinSubstitution([FindExecutable(name = "xacro")]),
            " ",
            PathJoinSubstitution(
                [FindPackageShare("h1_description"), "urdf", "h1.xacro"]
            ),
            ' if_add_axisgroups:=', if_add_axisgroups,
            ' if_add_external_device:=', if_add_external_device,
        ]
    )
    robot_description = {"robot_description": robot_description_content}

    moveit_config = MoveItConfigsBuilder("h1_robot").to_moveit_configs()
    
    run_motion_plan_demo_node = Node(
        package="hyy_control_interface",
        executable="motion_plan_demo",
        output="screen",
        parameters=[
            moveit_config.to_dict(),
            robot_description
        ],
    )
    
    return LaunchDescription(
        declared_arguments +
        [
            run_motion_plan_demo_node
        ]
    )

there is a flaw that i have to repeat robot_description prase in each launch file, honestly,i have start robot_state_publisher node,so if i can listen to the topic /robot_description instead of xacro parse. is there any tourials and examples?

Answer 1

The ideal solution would be that all your nodes directly subscribe to the /robot_description topic. It doesn't make sense that you subscribe to the topic inside the other launch files and pass the string as parameter to your nodes.