Simulating your First Robot

Create Directories

1- Create directories for the world and model files

$ mkdir /home/workspace/myrobot
$ cd /home/workspace/myrobot
$ mkdir world && mkdir model

Construct the Robot's Chassis

2- Launch Gazebo and switch to the Model Editor

First, launch Gazebo from the terminal:

$ gazebo

In Gazebo, click on edit -> Model Editor.

3- Create the robot chassis

In the model editor, drop a box anywhere in the scene and double click it to change its position and dimension as follows:
Make sure to scroll down to the bottom to edit the object position

• Position : [X, Y, Z] = [0, 0, 0.2]
• Visual and Collision geometry : [X, Y, Z] = [0.3, 1.0, 0.1]

Attach Wheels to the Robot's Chassis

4- Construct the robot wheels

Insert a cylinder inside the scene and then edit its position and orientation:
Make sure to scroll down to the bottom to edit the object position.

• Z pose = 0.2
• Roll = 1.5707 rad
• Visual and Collision geometry : [Radius, Length] = [0.2, 0.1]

Then, create a copy of this wheel and paste it on the other side of the robot.

5- Connect wheels to the chassis via joints

• Joint Types : Revolute
• Parent : Chassis
• Child : Wheel
• Joint Axis : Z
• Align Links Joint 1: mid x; minimum y and reverse
• Align Links Joint 2: mid x; maximum y and reverse

6- Save the model file

• Model : Save it as robot in /home/workspace/myrobot/model
• Exit the Model Editor

7- Save the world file

• World : Save is as myworld in /home/workspace/myrobot/world
• Exit Gazebo

Launching Gazebo world file from disk

To load the world file with Gazebo open a terminal, change the working directory and launch it:

$ cd /home/workspace/myrobot/world/           
$ gazebo myworld  

SDF Format

As you learned earlier, world and model files in Gazebo are formatted using the Simulation Description Format or SDF for short. You can now open the contents of either the world file or model file and check to see if it follows the SDF format. To open the contents of the world file inside a terminal type in the following:

$ cd /home/workspace/myrobot/world/           
$ gedit myworld  

The SDF format in this world file should follow this general structure:

<?xml version="1.0" ?>
<sdf version="1.5">
  <world name="default">
    <physics type="ode">
      ...
    </physics>

    <scene>
      ...
    </scene>

    <model name="box">
      ...
    </model>

    <model name="sphere">
      ...
    </model>

    <light name="spotlight">
      ...
    </light>

  </world>
</sdf>

Next, you will learn how to write a Plugin to interact with your World in Gazebo.