Part of the wheel is under ground in gazebo [closed]

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I am using kinetic-ros. but in gazebo ,part of the wheel is going below ground.

<?xml version="1.0"?>
<robot name="tortoisebot">
  <gazebo>
    <plugin name="differential_drive_controller"
      filename="libgazebo_ros_diff_drive.so">
      <leftJoint>rear_left_joint</leftJoint>
      <rightJoint>rear_right_joint</rightJoint>
      <robotBaseFrame>base_link</robotBaseFrame>
      <wheelSeparation>0.35</wheelSeparation>
      <wheelDiameter>0.16</wheelDiameter>
      <publishWheelJointState>true</publishWheelJointState>
    </plugin>
  </gazebo>

  <link name="base_link">
    <inertial>
      <mass value="0.01"/>
      <inertia ixx="0.015" ixy="0" ixz="0" iyy="0.0375" iyz="0" izz="0.0375"/>
    </inertial>
    <visual>
      <geometry>
        <box size="0.6 0.3 0.3"/>
      </geometry>
      <material name="silver">
        <color rgba="0.75 0.75 0.75 1"/>
      </material>
    </visual>
    <collision>
      <geometry>
        <box size="0.6 0.3 0.3"/>
      </geometry>
    </collision>
  </link>

  <link name="front_right_wheel">
    <inertial>
      <mass value="0.001"/>
      <inertia ixx="5.1458e-5" ixy="0" ixz="0" iyy="5.1458e-5" iyz="0" izz="6.125e-5"/>
    </inertial>

    <visual>
      <geometry>
        <cylinder length="0.05" radius="0.08"/>
      </geometry>
      <material name="black">
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <kp>1</kp>
  </link>

  <joint name="front_right_wheel_joint" type="continuous">
    <axis xyz="0 0 1"/>
    <parent link="base_link"/>
    <child link="front_right_wheel"/>
    <origin rpy="-1.5708 0 0"  xyz="0.2825 -0.160 -00.10"/>
  </joint>

  <link name="front_left_wheel">
    <inertial>
      <mass value="0.001"/>
      <inertia ixx="5.1458e-5" ixy="0" ixz="0" iyy="5.1458e-5" iyz="0" izz="6.125e-5"/>
    </inertial>
    <visual>
      <geometry>
        <cylinder length="0.05" radius="0.08"/>
      </geometry>
      <material name="black">
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
  </link>

  <joint name="front_left_wheel_joint" type="continuous">
    <axis xyz="0 0 1"/>
    <parent link="base_link"/>
    <child link="front_left_wheel"/>
    <origin rpy="-1.5708 0 0"  xyz="0.2825 0.160 -00.10"/>
  </joint>

  <link name="rear_right_wheel">
    <inertial>
      <mass value="0.001"/>
      <inertia ixx="5.1458e-5" ixy="0" ixz="0" iyy="5.1458e-5" iyz="0" izz="6.125e-5"/>
    </inertial>

    <visual>
      <geometry>
        <cylinder length="0.05" radius="0.08"/>
      </geometry>
      <material name="black">
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
  </link>

  <joint name="rear_right_wheel_joint" type="continuous">
    <axis xyz="0 0 1"/>
    <parent link="base_link"/>
    <child link="rear_right_wheel"/>
    <origin rpy="-1.5708 0 0"  xyz="-0.2825 -0.160 -00.10"/>
  </joint>

  <link name="rear_left_wheel">
    <inertial>
      <mass value="0.001"/>
      <inertia ixx="5.1458e-5" ixy="0" ixz="0" iyy="5.1458e-5" iyz="0" izz="6.125e-5"/>
    </inertial>

    <visual>
      <geometry>
        <cylinder length="0.05" radius="0.08"/>
      </geometry>
      <material name="black">
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
  </link>

  <joint name="rear_left_wheel_joint" type="continuous">
    <axis xyz="0 0 1"/>
    <parent link="base_link"/>
    <child link="rear_left_wheel"/>
    <origin rpy="-1.5708 0 0"  xyz="-0.2825 0.160 -00.10"/>
  </joint>

  <link name="lidar_box">
    <inertial>
      <mass value="0.0001"/>
      <inertia ixx="0.00023" ixy="0" ixz="0" iyy="0.0023" iyz="0" izz="0.00023"/>
    </inertial>
    <visual>  
      <geometry>
        <box size="0.1 0.1 0.1"/>
      </geometry>
      <material name="silver"/>
    </visual>
  </link>

  <joint name="lidar_joint" type="fixed">
    <parent link="base_link"/>
    <child link="lidar_box"/>
    <origin rpy="0 0 0" xyz="0 0 0.2"/>
  </joint>
</robot>