[ROS2 Q&A] How to spawn robot from sam_bot nav2 tutorial #237

18/11/2022

What we are going to learn

How to create a ROS 2 package
How to load a URDF robot for the Gazebo simulator

List of resources used in this post

Use the rosject: https://app.theconstructsim.com/l/50fbfe47/
The Construct: https://app.theconstructsim.com/
Nav2 documentation: https://navigation.ros.org/setup_guides/index.html
ROS2 Courses –▸
1. ROS2 Basics in 5 Days (Python): https://app.theconstructsim.com/#/Course/73
2. ROS2 Basics in 5 Days (C++): https://app.theconstructsim.com/#/Course/61
3. ROS2 Navigation (Galactic): https://app.theconstructsim.com/Course/109
4. ROS2 Navigation training: https://www.theconstruct.ai/ros2-navigation-training/

Overview

This post answers the following question posted at ROS answers:

https://answers.ros.org/question/407374/sam_bot-tutorial-gazebo-missing-wheels/

ROS Inside!

ROS inside

Before anything else, in case you want to use the logo above on your own robot or computer, feel free to download it for free and attach it to your robot. It is really free. Find it in the link below:

ROS Inside logo

Opening the rosject

In order to follow this tutorial, we need to have ROS2 installed in our system, and ideally a ros2_ws (ROS2 Workspace). To make your life easier, we already prepared a rosject with a simulation for that: https://app.theconstructsim.com/l/50fbfe47/.

You can download the rosject on your own computer if you want to work locally, but just by copying the rosject (clicking the link), you will have a setup already prepared for you.

After the rosject has been successfully copied to your own area, you should see a Run button. Just click that button to launch the rosject (below you have a rosject example).

Learn ROS2 Topics vs Service vs Action – Run rosject (example of the RUN button)

After pressing the Run button, you should have the rosject loaded. Now, let’s head to the next section to get some real practice.

Opening the Code Editor

Now that the rosject is open, let’s open the Code Editor by clicking on the second link:

Open the IDE – Code Editor

Once the Code Editor is open, you should be able to see that we have a ros2_ws folder (ROS2 workspace)

The sam_bot_description.urdf file

Now that you have the Code Editor open, let’s have a look at the file that contains the robot description. The file is inside the ros2_ws folder. The full path is:

/home/user/ros2_ws/src/sam_bot_description/src/description/sam_bot_description.urdf

In case you want to see the content using the terminal, you can open it by clicking the Open a new terminal button.

Open a new Terminal

Once inside the terminal, just type the command below (although it is better to see the file using the Code Editor):

cat /home/user/ros2_ws/src/sam_bot_description/src/description/sam_bot_description.urdf

Starting the simulation

As we saw in the overview, the question asked in ROS Answers was saying that the robot wheels were not working. That happened probably because the person forgot to add something to the URDF file.

To better understand the URDF file, you can refer to the Nav 2 Documentation: https://navigation.ros.org/setup_guides/urdf/setup_urdf.html and https://navigation.ros.org/setup_guides/odom/setup_odom.html

Now, go to the terminal you have open and run the following command to run the simulation:

ros2 launch  sam_bot_description display.launch.py

If everything went well, you should have Gazebo as well as RViz open, like in the image below (If the Graphical Tools don’t open automatically, just click click the 4th and 5th buttons on the bottom left bar to Open Gazebo and Open the Graphical Tools):

You can also see the Gazebo simulation by clicking the 4th icon named Open Gazebo. There you will see that the wheels are in place.

Well, that is pretty much it.

We hope this post was really helpful to you. If you want a live version of this post with more details, please check the video in the next section.

Youtube video

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Keep pushing your ROS Learning.