Gazebo is an independent Simulation Tool. gazebo_ros package can bridge Gazebo and ROS environment.
Credit: Robotics Backend (https://www.youtube.com/@RoboticsBackEnd)
In gazebo, there are many plugins to control the robot. Those plugins simulate real physical robot's encoders, wheels, etc.
Resources:
http://wiki.ros.org/urdf/Tutorials/Adding%20Physical%20and%20Collision%20Properties%20to%20a%20URDF%20Model
List of moments of Inertia: https://en.wikipedia.org/wiki/List_of_moments_of_inertia#List_of_3D_inertia_tensors
Step 1: Add inertia for box, cylinder, and sphere as xacro:maco(like creating a function) in common_properties.xacro file like
<xacro:macro name="box_inertia" params="m l w h xyz rpy ">
<inertial>
<origin xyz="${xyz}" rpy="${rpy}"/>
<mass value="${m}"/>
<inertia ixx="${(m/12) * (h*h + l*l)}" ixy="0.0" ixz="0.0"
iyy="${(m/12) * (w*w + l*l)}" iyz="0.0" izz="${(m/12) * (w*w + h*h)}" />
</inertial>
</xacro:macro>Step 2: Provide inertia as a parameter for each link in mobile_base.xacro file like
<xacro:box_inertia m="5.0" l="${base_length}" w="${base_width}" h="${base_height}"
xyz="0 0 ${base_height/2.0}" rpy="0 0 0" />Step 3: Add Collision(now copy of geometry and origin) like
<collision>
<geometry>
<box size="${base_length} ${base_width} ${base_height}"/>
</geometry>
<origin xyz="0 0 ${base_height/2.0}" rpy="0 0 0"/>
</collision>so the full code becomes
Code : my_robot.urdf.xacro
Credit: https://www.youtube.com/@RoboticsBackEnd
<?xml version="1.0"?>
<robot name="my_robot" xmlns:xacro="http://www.ros.org/wiki/xacro">
<xacro:include filename="common_properties.xacro"/>
<xacro:include filename="mobile_base.xacro"/>
</robot>Code : common_properties.xacro
Credit: https://www.youtube.com/@RoboticsBackEnd
<?xml version="1.0"?>
<robot xmlns:xacro="http://www.ros.org/wiki/xacro">
<material name="blue">
<color rgba="0 0 0.5 1" />
</material>
<material name="grey">
<color rgba="0.5 0.5 0.5 1" />
</material>
<xacro:macro name="box_inertia" params="m l w h xyz rpy">
<inertial>
<origin xyz="${xyz}" rpy="${rpy}" />
<mass value="${m}" />
<inertia ixx="${(m/12) * (h*h + l*l)}" ixy="0" ixz="0"
iyy="${(m/12) * (w*w + l*l)}" iyz="0"
izz="${(m/12) * (w*w + h*h)}" />
</inertial>
</xacro:macro>
<xacro:macro name="cylinder_inertia" params="m r h xyz rpy">
<inertial>
<origin xyz="${xyz}" rpy="${rpy}" />
<mass value="${m}" />
<inertia ixx="${(m/12) * (3*r*r + h*h)}" ixy="0" ixz="0"
iyy="${(m/12) * (3*r*r + h*h)}" iyz="0"
izz="${(m/2) * (r*r)}" />
</inertial>
</xacro:macro>
<xacro:macro name="sphere_inertia" params="m r xyz rpy">
<inertial>
<origin xyz="${xyz}" rpy="${rpy}" />
<mass value="${m}" />
<inertia ixx="${(2/5) * m * r * r}" ixy="0" ixz="0"
iyy="${(2/5) * m * r * r}" iyz="0"
izz="${(2/5) * m * r * r}" />
</inertial>
</xacro:macro>
</robot>Code : mobile_base.xacro
Credit: https://www.youtube.com/@RoboticsBackEnd
<?xml version="1.0"?>
<robot xmlns:xacro="http://www.ros.org/wiki/xacro">
<xacro:property name="base_length" value="0.6" />
<xacro:property name="base_width" value="0.4" />
<xacro:property name="base_height" value="0.2" />
<xacro:property name="wheel_radius" value="0.1" />
<xacro:property name="wheel_length" value="0.05" />
<link name="base_footprint" />
<link name="base_link">
<visual>
<geometry>
<box size="${base_length} ${base_width} ${base_height}" />
</geometry>
<origin xyz="0 0 ${base_height / 2.0}" rpy="0 0 0" />
<material name="blue" />
</visual>
<collision>
<geometry>
<box size="${base_length} ${base_width} ${base_height}"/>
</geometry>
<origin xyz="0 0 ${base_height/2.0}" rpy="0 0 0"/>
</collision>
<xacro:box_inertia m="5.0" l="${base_length}" w="${base_width}" h="${base_height}"
xyz="0 0 ${base_height / 2.0}" rpy="0 0 0" />
</link>
<xacro:macro name="wheel_link" params="prefix">
<link name="${prefix}_wheel_link">
<visual>
<geometry>
<cylinder radius="${wheel_radius}" length="${wheel_length}" />
</geometry>
<origin xyz="0 0 0" rpy="${pi / 2.0} 0 0" />
<material name="grey" />
</visual>
<collision>
<geometry>
<cylinder radius= "${wheel_radius}" length="${wheel_length}"/>
</geometry>
<origin xyz="0.0 0.0 0.0" rpy="${pi/2.0} 0.0 0.0"/>
</collision>
<xacro:cylinder_inertia m="1.0" r="${wheel_radius}" h="${wheel_length}"
xyz="0 0 0" rpy="${pi / 2.0} 0 0" />
</link>
</xacro:macro>
<xacro:wheel_link prefix="right" />
<xacro:wheel_link prefix="left" />
<link name="caster_wheel_link">
<visual>
<geometry>
<sphere radius="${wheel_radius / 2.0}" />
</geometry>
<origin xyz="0 0 0" rpy="0 0 0" />
<material name="grey" />
</visual>
<collision>
<geometry>
<sphere radius="${wheel_radius/2.0}"/>
</geometry>
<origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/>
</collision>
<xacro:sphere_inertia m="0.5" r="${wheel_radius / 2.0}"
xyz="0 0 0" rpy="0 0 0" />
</link>
<joint name="base_joint" type="fixed">
<parent link="base_footprint" />
<child link="base_link" />
<origin xyz="0 0 ${wheel_radius}" rpy="0 0 0"/>
</joint>
<joint name="base_right_wheel_joint" type="continuous">
<parent link="base_link" />
<child link="right_wheel_link" />
<origin xyz="${-base_length / 4.0} ${-(base_width + wheel_length) / 2.0} 0" rpy="0 0 0" />
<axis xyz="0 1 0" />
</joint>
<joint name="base_left_wheel_joint" type="continuous">
<parent link="base_link" />
<child link="left_wheel_link" />
<origin xyz="${-base_length / 4.0} ${(base_width + wheel_length) / 2.0} 0" rpy="0 0 0" />
<axis xyz="0 1 0" />
</joint>
<joint name="base_caster_wheel_joint" type="fixed">
<parent link="base_link" />
<child link="caster_wheel_link" />
<origin xyz="${base_length / 3.0} 0 ${-wheel_radius / 2.0}" rpy="0 0 0" />
</joint>
</robot>Step 1:
ros2 run robot_state_publisher robot_state_publisher --ros-args -p robot_description:="$(xacro ~/ros2_ws/src/my_robot_description/urdf/my_robot.urdf.xacro)"
Step 2: (in another terminal)
ros2 launch gazebo_ros gazebo.launch.py
Step 3: (in another terminal)
ros2 run gazebo_ros spawn_entity.py -topic robot_description -entity my_robot_1