Blog: ROS | The Construct

[ROS Q&A] 080 – How to make custom ROS Action

About

In this tutorial, we will learn how to create and compile a custom ROS Action from zero by answering a real question from ROS.Answers.

Below are the Steps to create the project as shown in the video

Step 1

Head to ROS Development Studio and create a new project.
Provide a suitable project name and some useful description. (We have named the project how_to_make_custom_ros_action)
Load/Start the project (this will take a few seconds).
Let’s create a new catkin package in our catkin workspace. Open Tools > Shell and run the following commands

$ cd catkin_ws/src
$ catkin_create_pkg turtlebot3_console_controller actionlib_msgs std_msgs

We’ll create an action directory to put the action file. We will create an action file named Motor.action inside the action directory

$ cd turtlebot3_console_controller
$ mkdir action
$ touch Motor.action

Use Tools > IDE to browse the directory and file we just created. At this point we should have the following directory structure

.
├── ai_ws
├── catkin_ws
│   ├── build
│   ├── devel
│   └── src
│       ├── CMakeLists.txt
│       └── turtlebot3_console_controller
│           ├── action
│           │   └── Motor.action
│           ├── CMakeLists.txt
│           └── package.xml
├── how_to_make_custom_ros_action.zip
├── notebook_ws
│   ├── default.ipynb
│   └── images
└── simulation_ws
  ├── build
  ├── devel
  └── src

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.

Related courses

Webinar | How to train your technical team on ROS skills?

Learn the method of how to train the technical team or interns on ROS skills fast. Already used by many Universities and companies.

ROS is becoming the essential skills for robotics engineers. Apart from labs, there is an increasing number of commercial sector, industrial and services robots using ROS. Gradually, it has become a widely-used platform in the robotics research community.

Is a “good solution” for companies who are seeking quick development. In recent year there is a high demand in the self-driving car industry and due to its low level of functionality benefits, it attracts a larger number start-up companies using it from warehousing to agriculture, which is growing at an exponential pace. It supports the robot development and industry growth without specifically costs for building software and hardware.

But as you may understand, robotics engineers spend a lot of time developing ROS based software. Sometimes, they need to gather more knowledge about a specific ROS subject. Sometimes the team needs to incorporate more engineers with ROS knowledge.

In order to speed things up, in this one-hour webinar we will show how to smooth learning path for your team in order to maximize their learning speed and get the best possible results.

WHO SHOULD WATCH?

Technical teams, robotics start-ups, and companies who need to equip their team or their interns on ROS in an effective way, and apply ROS into robotics development quickly and effectively.

More info about ROS Team Training: https://www.theconstruct.ai/ros-team-training/

[ROS Q&A] 079 – add AR tag in gazebo

Learn how to add an AR 3D element in GAzebo to use it for your AR tracking programs: https://answers.ros.org/question/240392/add-ar-tag-in-gazebo/

Q: add AR tag in gazebo
A: You have to generate the AR tag , then create the 3D model with the texture in blender and finally import it and spawn it in gazebo.

[ROS Q&A] 078 – ROS Remap

Q: Remapping between nodes
How to remap between nodes in launch file. Plz guide.im using Ros indigo version

A: Basically, remap is a feature to rename topics, node names and some special keys of ROS env. You can see in this page what you can remap, like a node name (__node), namespace (__ns), log file (__log), etc.

Example: I’ve a node that publishes Twist messages in a topic called turtlebot_vel, but my robot listens to cmd_vel

You can remap using rosrun command, like this: