Gazebo Physics

Introduction to Gazebo

Gazebo is an open-source 3D robot simulator. It's often used with ROS to simulate complex robot behaviors in realistic environments. Gazebo provides robust physics, high-quality graphics, and convenient programmatic interfaces.

Key Features of Gazebo

• Physics Engine: Supports various physics engines (ODE, Bullet, DART, Simbody) for accurate simulation of forces, friction, and collisions.
• Sensors: Simulates a wide range of sensors including cameras, LIDAR, IMUs, force-torque sensors, and more.
• Models: Allows importing and creating 3D models of robots and environments.
• Plugins: Extensible architecture to add custom functionalities and integrate with external software like ROS.

Simulating Physics

In Gazebo, you can define properties for your robot and environment models that influence their physical behavior:

• Mass and Inertia: Essential for realistic dynamics.
• Friction: Affects how objects slide or roll against each other.
• Restitution: Determines the "bounciness" of collisions.

Example: Simple Pendulum in SDF

Gazebo uses SDF (Simulation Description Format) to define environments and robots.

<?xml version="1.0" ?>
<sdf version="1.6">
  <model name="simple_pendulum">
    <link name="base_link">
      <pose>0 0 1 0 0 0</pose>
      <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>
      <visual name="visual">
        <geometry>
          <box>
            <size>0.1 0.1 0.1</size>
          </box>
        </geometry>
      </visual>
      <collision name="collision">
        <geometry>
          <box>
            <size>0.1 0.1 0.1</size>
          </box>
        </geometry>
      </collision>
    </link>

    <link name="pendulum_link">
      <pose>0 0 0.5 0 0 0</pose>
      <inertial>
        <mass>0.5</mass>
        <inertia>
          <ixx>0.005</ixx><ixy>0</ixy><ixz>0</ixz>
          <iyy>0.005</iyy><iyz>0</iyz>
          <izz>0.005</izz>
        </inertia>
      </inertial>
      <visual name="visual">
        <geometry>
          <cylinder>
            <radius>0.02</radius>
            <length>1.0</length>
          </cylinder>
        </geometry>
      </visual>
      <collision name="collision">
        <geometry>
          <cylinder>
            <radius>0.02</radius>
            <length>1.0</length>
          </cylinder>
        </geometry>
      </collision>
    </link>

    <joint name="pendulum_joint" type="revolute">
      <parent>base_link</parent>
      <child>pendulum_link</child>
      <pose>0 0 0 0 0 0</pose>
      <axis>
        <xyz>0 1 0</xyz>
      </axis>
    </joint>
  </model>
</sdf>