I use the book example to try, but it always wrong. The code is

<?xml version="1.0"?>

<include filename="$(find erratic_description)/urdf/erratic_hokuyo_laser.xacro" />

    <!-- BASE LASER ATTACHMENT -->
    <erratic_hokuyo_laser parent="base_link">
            <origin xyz="0.18 0 0.11" rpy="0 0 0" />
    </erratic_hokuyo_laser>


<xacro:property name="length_wheel" value="0.05" />
<xacro:property name="radius_wheel" value="0.05" />
<xacro:macro name="default_inertial" params="mass">
           <inertial>
                   <mass value="${mass}" />
                   <inertia ixx="1.0" ixy="0.0" ixz="0.0"
                            iyy="1.0" iyz="0.0"
                            izz="1.0" />
           </inertial>
</xacro:macro>

<link name="base_footprint">
    <visual>
        <geometry>
                <box size="0.001 0.001 0.001"/>
            </geometry>
        <origin rpy="0 0 0" xyz="0 0 0"/>
    </visual>
    <xacro:default_inertial mass="0.0001"/>
</link>

<gazebo reference="base_footprint">
    <material>Gazebo/Green</material>
    <turnGravityOff>false</turnGravityOff>
</gazebo>

<joint name="base_footprint_joint" type="fixed">
    <origin xyz="0 0 0" />
    <parent link="base_footprint" />
    <child link="base_link" />
</joint>


<link name="base_link">
    <visual>
        <geometry>
                <box size="0.2 .3 .1"/>
            </geometry>
        <origin rpy="0 0 1.54" xyz="0 0 0.05"/>
        <material name="white">
            <color rgba="1 1 1 1"/>
        </material>
    </visual>
    <collision>
        <geometry>
                <box size="0.2 .3 0.1"/>
        </geometry>
    </collision>
    <xacro:default_inertial mass="10"/>
</link>

<link name="wheel_1">
    <visual>
            <geometry>
                <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
            </geometry>
        <!-- <origin rpy="0 1.5 0" xyz="0.1 0.1 0"/> -->
        <origin rpy="0 0 0" xyz="0 0 0"/>
        <material name="black">
            <color rgba="0 0 0 1"/>
        </material>
    </visual>
    <collision>
        <geometry>
                <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
        </geometry>
    </collision>
    <xacro:default_inertial mass="1"/>
</link>

<link name="wheel_2">
    <visual>
            <geometry>
                <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
            </geometry>
        <!-- <origin rpy="0 1.5 0" xyz="-0.1 0.1 0"/> -->
        <origin rpy="0 0 0" xyz="0 0 0"/>
        <material name="black"/>
    </visual>
    <collision>
        <geometry>
                <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
        </geometry>
    </collision>
    <xacro:default_inertial mass="1"/>

</link>

<link name="wheel_3">
    <visual>
            <geometry>
                <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
            </geometry>
        <!-- <origin rpy="0 1.5 0" xyz="0.1 -0.1 0"/> -->

        <origin rpy="0 0 0" xyz="0 0 0"/>
        <material name="black"/>
    </visual>
    <collision>
        <geometry>
                <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
        </geometry>
    </collision>
    <xacro:default_inertial mass="1"/>
</link>

<link name="wheel_4">
    <visual>
            <geometry>
                <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
            </geometry>
    <!--    <origin rpy="0 1.5 0" xyz="-0.1 -0.1 0"/> -->
        <origin rpy="0 0 0" xyz="0 0 0" />
        <material name="black"/>
    </visual>
    <collision>
        <geometry>
                <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
        </geometry>
    </collision>
    <xacro:default_inertial mass="1"/>

</link>

Erratic/BlueBrushedAluminum

Erratic/Black

Erratic/Black

Erratic/Black

Erratic/Black

And the error is Error [parser.cc:697] XML Element[sensor:ray], child of element[link] not defined in SDF. Ignoring.[link] Error [parser.cc:688] Error reading element Error [parser.cc:688] Error reading element Error [parser.cc:348] Unable to read element Error [parser.cc:299] parse as old deprecated model file failed. Error [World.cc:1527] Unable to read sdf string

someone can help me?

If I delete this part,it can work.But after after add it, it will wrong.

<!-- BASE LASER ATTACHMENT -->
<erratic_hokuyo_laser parent="base_link">
        <origin xyz="0.18 0 0.11" rpy="0 0 0" />
</erratic_hokuyo_laser>