[Gazebo in 5 minutes] 003 – How to spawn a robot in gazebo

What you will learn

• Learn how to spawn a robot from its package in any gazebo simulation you may have running

List of resources used in this post:

• Two-wheeled Robot Repository: https://bitbucket.org/theconstructcore/two-wheeled-robot-simulation/src/master/
• Robot Ignite Academy, the place to learn to program robots using only a web browser
• ROS Development Studio (the environment used in the video), another powerful online tool for pushing your ROS learning in a practical way

Preparing the environment

In order to spawn a gazebo model in a simulation using ROS, you need to have Gazebo and ROS installed. If you don’t want to install everything, we highly recommend using ROSDS (ROS Development Studio) which gives you access to an online environment with ROS already installed. Indeed, we are going to use that tool for easiness. You can follow the same steps on your computer as well if you don’t want to use ROSDS.

To use ROSDS, you can just create an account and start using it.

Once you have your account created, you have to create a ROSject by clicking on the New ROSject button:

Once you have the ROSject, you can open it by clicking Open:

Spawning a two-wheeled robot in a gazebo simulation

When you open a ROSject, you are able to open web shell, code editor, etc.

Let’s start opening a web shell by clicking Tools -> Shell in ROSDS. Once you have the shell, let’s clone the repository that contains the robot:

cd ~/simulation_ws/src/

git clone https://bitbucket.org/theconstructcore/two-wheeled-robot-simulation

If you see, the repository we just cloned, you will find the file m2wr_description/launch/spawn.launch which contains the code used to spawn the robot. The code is as follows:

<?xml version="1.0" encoding="UTF-8"?>
<launch>
    <param name="robot_description" command="$(find xacro)/xacro --inorder '$(find m2wr_description)/urdf/m2wr.xacro'" />
    
    <arg name="x" default="0"/>
    <arg name="y" default="0"/>
    <arg name="z" default="0.5"/>
    
    <node name="mybot_spawn" pkg="gazebo_ros" type="spawn_model" output="screen"
          args="-urdf -param robot_description -model m2wr -x $(arg x) -y $(arg y) -z $(arg z)" />
          
</launch>

A quick look into this file shows that the file loaded in gazebo will be the m2wr_description/urdf/m2wr.xacro, in the positions xyz = 0, 0, 0.5.

Now, to actually spawn the robot, you can first load an empty world by clicking Simulations -> Empty World -> Start Simulation.

Starting an empty simulation in ROSDS

With the empty simulation running, we can now spawn our robot into the current simulation. For that, let’s first compile the workspace to make sure the package we cloned is ok:

cd ~/simulation_ws/
catkin_make
source devel/setup.bash
rospack profile

Now let’s spawn our robot:

roslaunch m2wr_description spawn.launch

If everything went as expected, you should have the two-wheeled robot in the simulation:

A two-whelled robot running in ROSDS

Congratulations!!! You just learned how to spawn a robot in a gazebo simulation.

Youtube video

If you didn’t understand well all the steps explained here or need more understanding of the files we created, remember that we have the live version of this post on YouTube. Also, if you liked the content, please consider subscribing to our youtube channel. We are publishing new content ~every day.

Keep pushing your ROS Learning.

Links & Resources mentioned in the video:

• Two-Wheeled Robot Repository
• Related courses:

  • 

    URDF for Robot Modeling Course

  • 

    ROS for Beginners Course

[Gazebo in 5 minutes] 002 – How to add gazebo models to a simulation

What you will learn

• Learn how to add a gazebo model to a running gazebo simulation

List of resources used in this post:

• Robot Ignite Academy, the place to learn to program robots using only a web browser
• ROS Development Studio (the environment used in the video), another powerful online tool for pushing your ROS learning in a practical way
• Gazebo models repository where you can find different models to be spawned

Including our model in the .world file

In this post, we are assuming you already have created a ROS package called my_simulations  and the following files: ~/simulation_ws/src/my_simulations/launch/my_world.launch and ~/simulation_ws/src/my_simulations/world/empty_world.world.

If you don’t have these files, please remember to first follow the previous post: https://www.theconstruct.ai/gazebo-5-mins-launch-first-gazebo-world-using-ros/

If you check the my_world.world file, from the previous post we have the following content:

<?xml version="1.0" ?>

<sdf version="1.5">
	<world name="default">
		<!-- A global light source -->
		<include>
			<uri>model://sun</uri>
		</include>

		<!-- A ground plane -->
		<include>
			<uri>model://ground_plane</uri>
		</include>
	</world>
</sdf>

Let’s add a postbox model. Remember that you can find many Gazebo moels on the Gazebo models repository.

The final content of ~/simulation_ws/src/my_simulations/world/empty_world.world after adding the postbox would be:

<?xml version="1.0" ?>

<sdf version="1.5">
	<world name="default">
		<!-- A global light source -->
		<include>
			<uri>model://sun</uri>
		</include>

		<!-- A ground plane -->
		<include>
			<uri>model://ground_plane</uri>
		</include>

                <!-- A post box plane -->
		<include>
			<uri>model://postbox</uri>
		</include>        

	</world>
</sdf>

This adds a model called postbox in the initial position (x=0, y=0, z=0). If you want it in a different position, you can add a <pose> like in the example below:

<include>
  <uri>model://postbox</uri>
  <pose>2 1 0 0 0 0</pose>
</include>

Adding the gazebo model to the simulation

Now that we have our empty_world.world file set, we can start our simulation in two ways:

Option one: Click Simulation -> Choose File, then select my_world.launch. This should automatically load the web version of gazebo, called gzweb.

Postbox gazebo simulation loaded in ROSDS

Option two: If you are running the tests on your computer, or you want to manually run the simulation, you can just:

source ~/simulation_ws/devel/setup.bash
roslaunch my_simulations my_world.launch --screen

If you are in ROSDS and chose to run the simulation manually, then you have to manually open the Gazebo Web (gzweb) by clicking on Tools -> Gazebo.

Congratulations. You have successfully loaded a custom model in a Gazebo World using ROS.

Youtube video

If you didn’t understand well all the steps explained here or needs more understanding of the files we created, remember that we have the live version of this post on YouTube. Also, if you liked the content, please consider subscribing to our youtube channel. We are publishing new content ~every day.

Keep pushing your ROS Learning.