The start_dynamixel launch file starts Dynamixel Control Manager, which can establish a connection to a USB-to-Dynamixel adapter and Dynamixel servos. Here is the definition of this launch file:

    <!-- This will open USB To Dynamixel controller and search for 
    servos --> 
    <launch> 
        <node name="dynamixel_manager" pkg="dynamixel_controllers"    
        type="controller_manager.py" required="true"      
      output="screen"> 
            <rosparam> 
                namespace: dxl_manager 
                serial_ports: 
                    pan_port: 
                        port_name: "/dev/ttyUSB0" 
                        baud_rate: 1000000 
                        min_motor_id: 1 
                        max_motor_id: 25 
                        update_rate: 20 
            </rosparam> 
        </node> 
    <!-- This will launch the Dynamixel pan controller --> 
      <include file="$(find      
    face_tracker_control)/launch/start_pan_controller.launch"/> 
    </launch> 

We have to mention the port_name (you can get the port number from kernel logs using the dmesg command). The baud_rate we configured was 1 Mbps, and the motor ID was 1. The controller_manager.py file will scan from servo ID 1 to 25 and report any servos being detected.

After detecting the servo, it will start the start_pan_controller.launch file, which will attach a ROS joint position controller for each servo.