Fixed model

<?xml version="1.0"?>
<robot name="test">

    <material name="black">
        <color rgba="0 0 0 1"/>
    </material>

    <material name="white">
        <color rgba="1 1 1 1"/>
    </material>

    <material name="red">
        <color rgba="1 0 0 1"/>
    </material>

    <material name="green">
        <color rgba="0 1 0 1"/>
    </material>

    <material name="blue">
        <color rgba="0 0 1 1"/>
    </material>

    <material name="grey">
        <color rgba=".2 .2 .2 1"/>
    </material>

    <link name="base_link">
        <visual>
            <geometry>
                <cylinder length="0.42" radius="0.02"/>
            </geometry>
            <origin rpy="1.57075 0 0" xyz="0 0 0"/>
            <material name="red"/>
        </visual>
    </link>

    <link name="f_axle">
        <visual>
            <geometry>
                <cylinder length="0.42" radius="0.02"/>
            </geometry>
            <origin rpy="0 1.57075 0" xyz="0 0.2 0"/>
        </visual>
    </link>

    <link name="r_axle">
        <visual>
            <geometry>
                <cylinder length="0.42" radius="0.02"/>
            </geometry>
            <origin rpy="0 1.57075 0" xyz="0 -0.2 0"/>
        </visual>
    </link>

        <link name="lf_wheel">
                <visual>
                        <geometry>
                                <cylinder length="0.075" radius="0.20"/>
                        </geometry>
            <origin rpy="0 1.57075 0" xyz="-0.2 -0.2 0"/>
                </visual>
        </link>

        <link name="rf_wheel">
                <visual>
                        <geometry>
                                <cylinder length="0.075" radius="0.20"/>
                        </geometry>
            <origin rpy="0 1.57075 0" xyz="0.2 -0.2 0"/>
                </visual>
        </link>

    <link name="lr_wheel">
                <visual>
                        <geometry>
                                <cylinder length="0.075" radius="0.20"/>
                        </geometry>
            <origin rpy="0 1.57075 0" xyz="0.2 0.2 0"/>
                </visual>
        </link>

    <link name="rr_wheel">
                <visual>
                        <geometry>
                                <cylinder length="0.075" radius="0.20"/>
                        </geometry>
            <origin rpy="0 1.57075 0" xyz="-0.2 0.2 0"/>
                </visual>
        </link>

    <joint name="f_axle_base_link" type="fixed">
    	<origin rpy="0 0 0" xyz="0 0 0"/>
        <parent link="base_link"/>
        <child link="f_axle"/>
    </joint>

    <joint name="r_axle_base_link" type="fixed">
    	<origin rpy="0 0 0" xyz="0 0 0"/>
        <parent link="base_link"/>
        <child link="r_axle"/>
    </joint>

    <joint name="f_axle_lf_wheel" type="fixed">
    	<origin rpy="0 0 0" xyz="0 0 0"/>
        <parent link="f_axle"/>
        <child link="lf_wheel"/>
    </joint>

    <joint name="f_axle_rf_wheel" type="fixed">
    	<origin rpy="0 0 0" xyz="0 0 0"/>
        <parent link="f_axle"/>
        <child link="rf_wheel"/>
    </joint>

    <joint name="r_axle_lr_wheel" type="fixed">
    	<origin rpy="0 0 0" xyz="0 0 0"/>
        <parent link="r_axle"/>
        <child link="lr_wheel"/>
    </joint>

    <joint name="r_axle_rr_wheel" type="fixed">
    	<origin rpy="0 0 0" xyz="0 0 0"/>
        <parent link="r_axle"/>
        <child link="rr_wheel"/>
    </joint>

</robot>