Step 2

• Open the Motor.action file in IDE and write the following content to it.

# This is an action definition file, which has three parts: the goal
# the result, and the feedback.
# Part 1: the goal.
#
# The angle in degree the robot to turn, sent by client main
float64 angle
---
# Part 2: the result, sent by action server unpon completion
#
# How much time used
duration time_elapsed
# How many updates thrown in total
uint32 updates_n
---
# Part 3: the feedback,to be sent periodically by server
#
# The amount of time elapsed from the start
duration time_elapsed

• The contents of Motor.action defines variables of three categories. The categories are separated by — lines. The first category of variables are related to GOAL, second is related to RESULT and third are related to the FEEDBACK. Here we have the following variable in different categories: angle for GOAL, time_elapsed, updates_n for RESULT and time_elapsed for FEEDBACK.

• Now we have to add the directive to compile action file in CMakeLists.txt file. This file is inside our package directory i.e. ~/catkin_ws/src/turtlebot3_console_controller. Open the CMakeLists.txt file in IDE
• Add the following code block

  add_action_files(
  FILES
  Motor.action
  )
  

• Also, add this code block

  generate_messages(
  DEPENDENCIES
  actionlib_msgs
  )
  

• Let’s compile the project. Run following commands in the SHELL
  

  $ cd ~/catkin_ws

  $ catkin_make

• To test if the action file works we will create a script name node.py inside a new directory within the package. Use the following commands in SHELL
  

  $ cd ~/catkin_ws/src/turtlebot3_console_controller

  $ mkdir src

  $ touch node.py

• To create the directory and file we can use IDE tool as well. Let’s add the following code to the node.py file

from turtlebot3_console_controller.msg import MotorGoal, MotorResult, MotorFeedback 

print("OK, it worked!!!")

Let’s run the above script. Enter the following commands in the SHELL

$ cd ~/catkin_ws/src/turtlebot3_console_controller/src

$ ./node.py

After running the above command you should see the reply OK, it worked!!! in the next line.

And that’s it. We have created a basic action message and verified it works.