"Failed to getParam 'joints' for effort_controllers/JointGroupPositionController" error resulting in failure to initialize the joint_group_position_controller

edit

I see that effort_controllers/JointPositionController looks for the particular joint and assigns the corresponding PID value to the control_toolbox::Pid variable. effort_controllers/JointGroupPositionController also does the same thing for all the joints inside the controller in a for loop. So essentially there is no difference between the two except for in the .yaml file and the launch files.

When I try to load a effort_controllers/JointGroupPositionController with the following .yaml file and launch file, I am getting the following error: "Failed to getParam 'joints' (namespace: /my_6dof_robot/joint_group_position_controller)".

[INFO] [1572904736.013589, 0.511000]: Controller Spawner: Waiting for service controller_manager/switch_controller
[INFO] [1572904736.015633, 0.512000]: Controller Spawner: Waiting for service controller_manager/unload_controller
[INFO] [1572904736.017165, 0.513000]: Loading controller: joint_group_position_controller
[ERROR] [1572904736.025517675, 0.519000000]: Failed to getParam 'joints' (namespace: /my_6dof_robot/joint_group_position_controller).
[ERROR] [1572904736.025622082, 0.519000000]: Failed to initialize the controller
[ERROR] [1572904736.025671797, 0.519000000]: Initializing controller 'joint_group_position_controller' failed
[ERROR] [1572904737.027262, 1.296000]: Failed to load joint_group_position_controller
[INFO] [1572904737.027650, 1.296000]: Loading controller: joint_state_controller
[INFO] [1572904737.035878, 1.303000]: Controller Spawner: Loaded controllers: joint_state_controller
[INFO] [1572904737.045714, 1.309000]: Started controllers: joint_state_controller

It succeeds in loading the joint_state_controller.

The .yaml file (my_6dof_robot_effort_control.yaml) is as follows:

my_6dof_robot:
  joint_state_controller:
    type: joint_state_controller/JointStateController
    publish_rate: 50
  joint_group_position_controller:
    type: effort_controllers/JointGroupPositionController
    joints:
      joint_base_link1: 
        pid: {p: 600.0, i: 80.0, d: 200.0}
      joint_link1_link2: 
        pid: {p: 11000.0, i: 100.0, d: 500.0}
      joint_link2_link3: 
        pid: {p: 8000.0, i: 300.0, d: 400.0}
      joint_link3_link4: 
        pid: {p: 400.0, i: 40.0, d: 60.0}
      joint_link4_link5: 
        pid: {p: 400.0, i: 10.0, d: 10.0}
      joint_link5_link6: 
        pid: {p: 20.0, i: 0.8, d: 0.1}

The gazebo and control launch file is as follows:

<launch>

  <arg name="paused" default="false"/>
  <arg name="use_sim_time" default="true"/>
  <arg name="gui" default="true"/>
  <arg name="headless" default="false"/>
  <arg name="debug" default="false"/>

  <include
    file="$(find gazebo_ros)/launch/empty_world.launch">
    <arg name="debug" value="$(arg debug)" />
    <arg name="gui" value="$(arg gui)" />
    <arg name="paused" value="$(arg paused)"/>
    <arg name="use_sim_time" value="$(arg use_sim_time)"/>
    <arg name="headless" value="$(arg headless)"/>
  </include>

    <param name="robot_description" command="$(find xacro)/xacro --inorder $(find my_6dof_robot_description)/urdf/my_6dof_robot_robot.xacro"/>
    <node name="spawn_my_6dof_robot" pkg="gazebo_ros" type="spawn_model" 
     args="-param robot_description
           -urdf 
           -x 0  
           -y 0
           -z 0
           -model my_6dof_robot"
     respawn="false" output="screen">
    </node>

    <rosparam file="$(find my_6dof_robot_control)/config/my_6dof_robot_effort_control.yaml" command="load" />


    <node name="controller_spawner" pkg="controller_manager" type="spawner" respawn="false" ns="/my_6dof_robot_robot"
      output="screen" args="joint_group_position_controller joint_state_controller --timeout 50">  
    </node>
    <node name = "robot_state_publisher" pkg = "robot_state_publisher" type = "robot_state_publisher" respawn="false" output="screen">
      <remap from="/joint_states" to="/my_6dof_robot_robot/joint_states" />
    </node>
</launch>

However, when I load the effort_controllers/JointPositionController with the following .yaml and launch file, it is a success.

my_6dof__robot:
  joint_state_controller:
    type: joint_state_controller/JointStateController
    publish_rate: 50
  joint1_position_controller:
    type: effort_controllers/JointPositionController
    joint: joint_base_link1
    pid: {p: 600.0, i: 80.0, d: 200.0}
  joint2_position_controller:
    type: effort_controllers ...