Look Away

To see a ROS subscriber and client in action, you'll write a node called look_away. The look_away node will subscribe to the /rgb_camera/image_raw topic, which has image data from the camera mounted on the end of the robotic arm. Whenever the camera is pointed towards an uninteresting image - in this case, an image with uniform color - the callback function will request a safe_move service to safely move the arm to something more interesting. There are a few extra pieces in the code to ensure that this procedure is executed smoothly, but we’ll focus on those later.

Updating the launch file

Just as you did with the arm_mover node, to get look_away to launch with the rest of the nodes, you will need to modify robot_spawn.launch, which can be found in /home/workspace/catkin_ws/src/simple_arm/launch. You can add the following code there:

  <!-- The look away node -->
  <node name="look_away" type="look_away" pkg="simple_arm"/>

Remember that a half turn of a joint requires pi/2 radians of revolution. Numerically, pi/2 is approximately 1.57. Since we want to be able to revolve a joint halfway around with one request, it will be helpful to set max_joint_2_angle: 1.57 in arm_mover:

  <!-- The arm mover node -->
  <node name="arm_mover" type="arm_mover" pkg="simple_arm">
    <rosparam>
      min_joint_1_angle: 0
      max_joint_1_angle: 1.57
      min_joint_2_angle: 0
      max_joint_2_angle: 1.57
    </rosparam>
  </node>