controller type 'position_controllers/JointTrajectoryController' does not exist.

edit

I try to follow a tutorial in the "Programming Robots with ROS" book. In this tutorial I want to show and move my own robot model in Gazebo. The URDF description loads correctly in Gazebo, the model is shown. Then I extended the URDF by dynamics and ros_control. When I launch the configuration, there are errors from gazebo_ros_control, that my controller could not be loaded.

controller type 'position_controllers/JointTrajectoryController' does not exist.

type: "position_controllers/JointTrajectoryController"

In my case this leads to the above error.

My controller definition:

arm_controller:
        type: "position_controllers/JointTrajectoryController"
        joints: 
                - hip
                - shoulder
                - elbow
                - wrist 
 

rosservice call controller_manager/list_controller_types
types: 
  - diff_drive_controller/DiffDriveController
  - joint_state_controller/JointStateController
  - position_controllers/JointGroupPositionController
  - position_controllers/JointPositionController
base_classes: 
  - controller_interface::ControllerBase
  - controller_interface::ControllerBase
  - controller_interface::ControllerBase
  - controller_interface::ControllerBase 

There it shows position_controllers only with JointPositionController. In this case my arm_controller is not found.

<launch>
 

<include file="$(find gazebo_ros)/launch/empty_world.launch"/>

<node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" args="-param robot_description -urdf -model my
robot"/>

<rosparam file="$(find myrobot)/controllers.yaml" command="load"/>

<node name="controller_spawner" pkg="controller_manager" type="spawner" args="arm_controller" output="scre
en"/>

</launch>
 

My Environment:

- Ubuntu focal

- ROS - noetic

Which is the correct way to follow, to bring my robot to life? rostopic list should show my arm_controller. But it is not loaded.