Gazebo Quickstart Guide

Prerequisites

Before starting with Gazebo simulation, ensure you have:

• ROS 2: Humble Hawksbill or later installed and sourced
• Gazebo Garden: Or compatible version installed
• Basic ROS 2 Knowledge: Understanding of topics, services, and launch files
• System Requirements:
  • 64-bit processor
  • 8GB+ RAM recommended
  • Compatible graphics card for visualization

Installation Verification

First, verify your Gazebo installation:

# Check Gazebo version
gz --version

# Check available simulators
gz sim --list

# Test basic functionality
gz sim

Creating Your First Simulation

1. Setting Up the Workspace

Create a workspace for your digital twin examples:

mkdir -p ~/digital_twin_ws/src
cd ~/digital_twin_ws
colcon build
source install/setup.bash

2. Basic World File

Create a simple world file simple_world.sdf in your workspace:

<?xml version="1.0" ?>
<sdf version="1.7">
  <world name="simple_world">
    <!-- Include standard models -->
    <include>
      <uri>model://ground_plane</uri>
    </include>
    <include>
      <uri>model://sun</uri>
    </include>

    <!-- Add a simple robot -->
    <model name="simple_robot">
      <pose>0 0 0.5 0 0 0</pose>
      <link name="chassis">
        <pose>0 0 0.15 0 0 0</pose>
        <collision name="collision">
          <geometry>
            <box>
              <size>0.5 0.3 0.3</size>
            </box>
          </geometry>
        </collision>
        <visual name="visual">
          <geometry>
            <box>
              <size>0.5 0.3 0.3</size>
            </geometry>
          </visual>
        <inertial>
          <mass>1.0</mass>
          <inertia>
            <ixx>0.01</ixx>
            <ixy>0</ixy>
            <ixz>0</ixz>
            <iyy>0.01</iyy>
            <iyz>0</iyz>
            <izz>0.01</izz>
          </inertia>
        </inertial>
      </link>
    </model>
  </world>
</sdf>

3. Launching the Simulation

Launch your simulation:

# Method 1: Direct Gazebo launch
gz sim -r simple_world.sdf

# Method 2: Using ROS 2 launch system
ros2 launch your_package simple_world.launch.py

Physics Properties Configuration

Gravity Settings

By default, Gazebo uses Earth's gravity (9.81 m/s²). To customize:

<physics name="1ms" type="ode">
  <gravity>0 0 -9.8</gravity>
  <max_step_size>0.001</max_step_size>
  <real_time_factor>1</real_time_factor>
  <real_time_update_rate>1000</real_time_update_rate>
</physics>

Collision Detection

Configure collision properties for your models:

<collision name="collision">
  <geometry>
    <box>
      <size>1 1 1</size>
    </box>
  </geometry>
  <surface>
    <friction>
      <ode>
        <mu>1.0</mu>
        <mu2>1.0</mu2>
      </ode>
    </friction>
    <bounce>
      <restitution_coefficient>0.1</restitution_coefficient>
      <threshold>100000</threshold>
    </bounce>
    <contact>
      <ode>
        <soft_cfm>0</soft_cfm>
        <soft_erp>0.2</soft_erp>
        <kp>1e+13</kp>
        <kd>1</kd>
        <max_vel>0.01</max_vel>
        <min_depth>0</min_depth>
      </ode>
    </contact>
  </surface>
</collision>

Basic Robot Model

URDF to SDF Conversion

Create a simple robot using URDF format and convert to SDF if needed:

<!-- simple_robot.urdf -->
<?xml version="1.0"?>
<robot name="simple_robot">
  <link name="base_link">
    <visual>
      <geometry>
        <box size="0.5 0.3 0.3"/>
      </geometry>
    </visual>
    <collision>
      <geometry>
        <box size="0.5 0.3 0.3"/>
      </geometry>
    </collision>
    <inertial>
      <mass value="1.0"/>
      <inertia ixx="0.01" ixy="0.0" ixz="0.0" iyy="0.01" iyz="0.0" izz="0.01"/>
    </inertial>
  </link>
</robot>

Launch Files

Create a ROS 2 launch file for your simulation:

# launch/simple_simulation.launch.py
from launch import LaunchDescription
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource
from launch.substitutions import PathJoinSubstitution
from launch_ros.substitutions import FindPackageShare

def generate_launch_description():
    world_file = PathJoinSubstitution([
        FindPackageShare('your_package'),
        'worlds',
        'simple_world.sdf'
    ])

    gz_sim = IncludeLaunchDescription(
        PythonLaunchDescriptionSource([
            FindPackageShare('gazebo_ros'),
            '/launch/gz_sim.launch.py'
        ]),
        launch_arguments={
            'world': world_file,
            'gz_args': '-r'  # Run simulation automatically
        }.items()
    )

    return LaunchDescription([
        gz_sim
    ])

Testing Gravity Effects

To verify gravity is working correctly:

1. Create a world with a robot model
2. Launch the simulation without any controllers
3. Observe the robot falling due to gravity
4. Check that the robot rests on the ground plane

Testing Collision Detection

To verify collision detection:

1. Create a world with multiple objects
2. Position objects to potentially collide
3. Launch simulation and observe collision behavior
4. Verify objects don't pass through each other

Common Issues and Solutions

Issue: Robot falls through ground

Solution: Check collision geometry and static properties

• Ensure ground plane has proper collision geometry
• Verify robot is not marked as static

Issue: Simulation is unstable

Solution: Adjust physics parameters

• Reduce max_step_size for better stability
• Adjust solver parameters in physics configuration

Issue: No visualization

Solution: Check graphics drivers and environment

• Ensure proper graphics drivers are installed
• Set proper display environment variables if using remote access

Issue: High CPU usage

Solution: Optimize simulation settings

• Increase max_step_size (reduces accuracy)
• Reduce real_time_update_rate
• Simplify collision geometry

Next Steps

After completing this quickstart guide, you should be able to:

• Create basic Gazebo world files
• Launch simulations with physics properties
• Verify gravity and collision behavior
• Configure basic robot models

Continue to the next section to learn about advanced physics properties and robot configurations.