In this section we are going to create two additional files named common_properties.xacro and moblie_base.xacro and have the code in the main file (my_robot.urdf.xacro) be split between these two files.

Let’s first create those files:

Code in the common_properties.xacro file is this:

<?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>

</robot>

Code in the moblie_base.xacro file is this:

<?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>
    </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>
        </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>
    </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>

Code in the my_robot.urdf.xacro file is this:

<?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>

To include a certain file in the main file we use this syntax:

<xacro:include filename="file_name" />