Completed URDF specified toy car.

simplecar.urdf

<?xml version="1.0"?> 
<robot name="simplecar">
    <!-- Colors --> 
    <material name="black"> 
        <color rgba="0 0 0 1"/>
    </material>
    <material name="blue"> 
        <color rgba="0.6 0.7 0.8 1"/>
    </material>


    <!-- Base Frame of Car --> 
    <link name="base_link">
        <visual> 
            <geometry> 
                <box size="0.5 0.3 0.1"/>
            </geometry>
            <material name="blue"/>
        </visual>
        <inertial> 
            <mass value="6"/>
            <inertia ixx="0.2" ixy="0" ixz="0" iyy="0.2" iyz="0.0" izz="0.2"/>
        </inertial> 
    </link> 


    <!-- Left Front Wheel -->
    <link name="left_front_wheel">
        <visual> 
            <geometry> 
                <cylinder length="0.05" radius="0.1"/>
            </geometry>
            <origin rpy="1.57075 1.57075 0"/>
            <material name="black"/>
        </visual>
        <collision> 
             <geometry> 
                <cylinder length="0.05" radius="0.1"/>
            </geometry>
            <origin rpy="1.57075 1.57075 0"/>
        </collision> 
        <inertial> 
            <origin rpy="1.57075 1.57075 0"/>
            <mass value="0.3"/>
            <inertia ixx="0.4" ixy="0" ixz="0" iyy="0.4" iyz="0.0" izz="0.2"/>
        </inertial> 
    </link> 
    <joint name="left_hinge_to_left_front_wheel" type="continuous">
        <parent link="left_hinge"/>
        <child link="left_front_wheel"/> 
        <axis xyz="0 1 0"/>
        <origin xyz="0 0.2 0"/>
    </joint>
    <!-- Left Front Wheel - Hinge -->
    <link name="left_hinge">
        <visual> 
            <geometry> 
                <box size="0.20 0.02 0.02"/>
            </geometry>
            <origin xyz="0 0.1 0 " rpy="0 0 1.57075"/>
            <material name="black"/>
        </visual>
        <inertial> 
            <origin rpy="0 0 1.57075"/>
            <mass value="0.01"/>
            <inertia ixx="5E-6" ixy="0" ixz="0" iyy="5E-6" iyz="0" izz="5E-6"/>
        </inertial> 
    </link> 
    <joint name="base_to_left_hinge" type="revolute">
        <parent link="base_link"/>
        <child link="left_hinge"/> 
        <axis xyz="0 0 1"/>
        <origin xyz="0.2 0.0 0"/>
        <limit effort="100" lower="-0.5" upper="0.5" velocity="100"/>
    </joint>
    <!-- Right Front Wheel -->
    <link name="right_front_wheel">
        <visual> 
            <geometry> 
                <cylinder length="0.05" radius="0.1"/>
            </geometry>
            <origin rpy="-1.57075 -1.57075 0"/>
            <material name="black"/>
        </visual>
        <collision> 
             <geometry> 
                <cylinder length="0.05" radius="0.1"/>
            </geometry>
            <origin rpy="-1.57075 -1.57075 0"/>
        </collision> 
        <inertial> 
            <origin rpy="-1.57075 -1.57075 0"/>
            <mass value="0.3"/>
            <inertia ixx="0.4" ixy="0" ixz="0" iyy="0.4" iyz="0.0" izz="0.2"/>
        </inertial> 
    </link> 
    <joint name="right_hinge_to_right_front_wheel" type="continuous">
        <parent link="right_hinge"/>
        <child link="right_front_wheel"/> 
        <axis xyz="0 1 0"/>
        <origin xyz="0 -0.2 0"/>
    </joint>
    <!-- Right Front Wheel - Hinge -->
    <link name="right_hinge">
        <visual> 
            <geometry> 
                <box size="0.20 0.02 0.02"/>
            </geometry>
            <origin xyz="0 -0.1 0 " rpy="0 0 -1.57075"/>
            <material name="black"/>
        </visual>
        <inertial> 
            <origin rpy="0 0 -1.57075"/>
            <mass value="0.01"/>
            <inertia ixx="5E-6" ixy="0" ixz="0" iyy="5E-6" iyz="0" izz="5E-6"/>
        </inertial> 
    </link> 
    <joint name="base_to_right_hinge" type="revolute">
        <parent link="base_link"/>
        <child link="right_hinge"/> 
        <axis xyz="0 0 1"/>
        <origin xyz="0.2 0 0"/>
        <limit effort="100" lower="-0.5" upper="0.5" velocity="100"/>
    </joint>
    <!-- Left Back Wheel -->
    <link name="left_back_wheel">
        <visual> 
            <geometry> 
                <cylinder length="0.05" radius="0.1"/>
            </geometry>
            <origin rpy="1.57075 1.57075 0"/>
            <material name="black"/>
        </visual>
        <collision> 
             <geometry> 
                <cylinder length="0.05" radius="0.1"/>
            </geometry>
            <origin rpy="1.57075 1.57075 0"/>
        </collision> 
        <inertial> 
            <origin rpy="1.57075 1.57075 0"/>
            <mass value="0.3"/>
            <inertia ixx="0.4" ixy="0" ixz="0" iyy="0.4" iyz="0.0" izz="0.2"/>
        </inertial> 
    </link> 
    <joint name="base_to_left_back_wheel" type="continuous">
        <parent link="base_link"/>
        <child link="left_back_wheel"/> 
        <axis xyz="0 1 0"/>
        <origin xyz="-0.2 0.175 0"/>
    </joint>
    <!-- Right Back Wheel -->
    <link name="right_back_wheel">
        <visual> 
            <geometry> 
                <cylinder length="0.05" radius="0.1"/>
            </geometry>
            <origin rpy="-1.57075 -1.57075 0"/>
            <material name="black"/>
        </visual>
        <collision> 
             <geometry> 
                <cylinder length="0.05" radius="0.1"/>
            </geometry>
            <origin rpy="-1.57075 -1.57075 0"/>
        </collision> 
        <inertial> 
            <origin rpy="-1.57075 -1.57075 0"/>
            <mass value="0.3"/>
            <inertia ixx="0.4" ixy="0" ixz="0" iyy="0.4" iyz="0.0" izz="0.2"/>
        </inertial> 
    </link> 
    <joint name="base_to_right_back_wheel" type="continuous">
        <parent link="base_link"/>
        <child link="right_back_wheel"/> 
        <axis xyz="0 1 0"/>
        <origin xyz="-0.2 -0.175 0"/>
    </joint>
</robot>