Interfacing robot controllers to each joint is a simple task. The first task is to write a configuration file for two controllers.

The joint state controllers will publish the joint states of the arm and the joint position controllers can receive a goal position for each joint and can move each joint.

We will find the configuration file for the controller at seven_dof_arm_gazebo_control.yaml in the seven_dof_arm_gazebo/config folder.

Here is the configuration file definition:

seven_dof_arm: 
  # Publish all joint states ----------------------------------- 
  joint_state_controller: 
    type: joint_state_controller/JointStateController 
    publish_rate: 50   
   
  # Position Controllers --------------------------------------- 
  joint1_position_controller: 
    type: position_controllers/JointPositionController 
    joint: shoulder_pan_joint 
    pid: {p: 100.0, i: 0.01, d: 10.0} 
  joint2_position_controller: 
    type: position_controllers/JointPositionController 
    joint: shoulder_pitch_joint 
    pid: {p: 100.0, i: 0.01, d: 10.0} 
  joint3_position_controller: 
    type: position_controllers/JointPositionController 
    joint: elbow_roll_joint 
    pid: {p: 100.0, i: 0.01, d: 10.0} 
  joint4_position_controller: 
    type: position_controllers/JointPositionController 
    joint: elbow_pitch_joint 
    pid: {p: 100.0, i: 0.01, d: 10.0} 
  joint5_position_controller: 
    type: position_controllers/JointPositionController 
    joint: wrist_roll_joint 
    pid: {p: 100.0, i: 0.01, d: 10.0} 
  joint6_position_controller: 
    type: position_controllers/JointPositionController 
    joint: wrist_pitch_joint 
    pid: {p: 100.0, i: 0.01, d: 10.0} 
  joint7_position_controller: 
    type: position_controllers/JointPositionController 
    joint: gripper_roll_joint 
    pid: {p: 100.0, i: 0.01, d: 10.0} 

We can see that all the controllers are inside the namespace seven_dof_arm, and the first line represents the joint state controllers, which will publish the joint state of the robot at the rate of 50 Hz.

The remaining controllers are joint position controllers, which are assigned to the first seven joints, and they also define the PID gains.