I have made a urdf for diff drive robot. here i am using gazeboroscontol plugin to control this motor similary like turtlebot3. But when i send the forward twist command the robot is rotating instead of moving forward. Here is my xacro file:

    <?xml version="1.0"?>
    <!-- Revolute-Revolute Manipulator -->
    <robot name="bini" xmlns:xacro="http://www.ros.org/wiki/xacro">



     <!-- Constants for robot dimensions -->
      <xacro:property name="PI" value="3.1415926535897931"/>
      <xacro:property name="mass" value="1" /> <!-- arbitrary value for mass -->
      <xacro:property name="width" value="0.1" /> <!-- Square dimensions (widthxwidth) of beams -->
      <xacro:property name="height1" value="2" /> <!-- Link 1 -->
      <xacro:property name="height2" value="1" /> <!-- Link 2 -->
      <xacro:property name="height3" value="1" /> <!-- Link 3 -->
      <xacro:property name="camera_link" value="0.05" /> <!-- Size of square 'camera' box -->
      <xacro:property name="axel_offset" value="0.05" /> <!-- Space btw top of beam and the each joint -->

  <!-- Modify this content if robots joint and link names are different -->
  <xacro:arg name="left_wheel_joint_name" default="left_wheel_joint"/>
  <xacro:arg name="right_wheel_joint_name" default="right_wheel_joint"/>
  <xacro:arg name="right_wheel_link_name" default="right_wheel"/>
  <xacro:arg name="left_wheel_link_name" default="left_wheel"/>
  <xacro:arg name="front_wheel_link_name" default="front_wheel"/>
  <xacro:arg name="back_wheel_link_name" default="back_wheel"/>
  <xacro:arg name="imu_link_name" default="imu_link"/>
  <xacro:arg name="lidar_link_name" default="base_scan"/>
  <xacro:arg name="camera_link_name" default="camera_link"/>

  <!-- Import all Gazebo-customization elements, including Gazebo colors -->
  <xacro:include filename="$(find bini_simulation)/urdf/bini.gazebo" />
  <!-- Import Rviz colors -->
  <xacro:include filename="$(find bini_simulation)/urdf/materials.xacro" />

  <!-- Import robot urdf which was directly exported from Solidwork-->
  <xacro:include filename="$(find bini_description)/urdf/bini_description.urdf" />

  <link name="base_footprint"/>

  <joint name="base_joint" type="fixed">
    <parent link="base_footprint"/>
    <child link="base_link" />
    <origin xyz="0.0167666250730711 -0.00206087262344925 0.0155567321901691" rpy="0 0 0"/>
  </joint>


      <!-- Transmission element segment for each moving joint in robot according to their type of control -->
      <transmission name="tran1">

    <type>transmission_interface/SimpleTransmission</type>
    <joint name="$(arg left_wheel_joint_name)">
      <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
    </joint>

    <actuator name="motor1">
      <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
      <mechanicalReduction>1</mechanicalReduction>
    </actuator>
      </transmission>

      <transmission name="tran2">
        <type>transmission_interface/SimpleTransmission</type>
        <joint name="$(arg right_wheel_joint_name)">
          <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
        </joint>
        <actuator name="motor2">
          <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
          <mechanicalReduction>1</mechanicalReduction>
        </actuator>
      </transmission>

    </robot>

The xacro file for gazebo plugin is:

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

      <!-- simulation parameters segment for given joint -->
      <gazebo reference="base_link">
        <material>Gazebo/DarkGrey</material>
      </gazebo>

      <gazebo reference="$(arg left_wheel_link_name)">
        <mu1>0.1</mu1>
        <mu2>0.1</mu2>
        <kp>500000.0</kp>
        <kd>10.0</kd>
        <minDepth>0.001</minDepth>
        <maxVel>0.1</maxVel>
        <fdir1>1 0 0</fdir1>
        <material>Gazebo/FlatBlack</material>
      </gazebo>

      <gazebo reference="$(arg right_wheel_link_name)">
    <mu1>0.1</mu1>
    <mu2>0.1</mu2>
    <kp>500000.0</kp>
    <kd>10.0</kd>
    <minDepth>0.001</minDepth>
    <maxVel>0.1</maxVel>
    <fdir1>1 0 0</fdir1>
    <material>Gazebo/FlatBlack</material>
  </gazebo>

  <gazebo reference="$(arg front_wheel_link_name)">
    <mu1>0.1</mu1>
    <mu2>0.1</mu2>
    <kp>1000000.0</kp>
    <kd>100.0</kd>
    <minDepth>0.001</minDepth>
    <maxVel>1.0</maxVel>
    <material>Gazebo/FlatBlack</material>
  </gazebo>

  <gazebo reference="$(arg back_wheel_link_name)">
    <mu1>0.1</mu1>
    <mu2>0.1</mu2>
    <kp>1000000.0</kp>
    <kd>100.0</kd>
    <minDepth>0.001</minDepth>
    <maxVel>1.0</maxVel>
    <material>Gazebo/FlatBlack</material>
  </gazebo>

  <gazebo reference="$(arg imu_link_name)">
    <sensor type="imu" name="imu">
      <always_on>true</always_on>
    </sensor>
    <material>Gazebo/Grey</material>
  </gazebo>

  <!-- gazebo ros plugin segment -->  
  <!-- gazebo_ros_control plugin -->
  <gazebo>
    <plugin name="gazebo_ros_control" filename="libgazebo_ros_control.so">
      <!-- <robotNamespace>/bini</robotNamespace> -->
      <robotSimType>gazebo_ros_control/DefaultRobotHWSim</robotSimType>
    </plugin>
  </gazebo>

  <!-- gazebo_ros_imu plugin -->
  <gazebo reference="$(arg imu_link_name)">
    <gravity>true</gravity>
    <sensor name="imu_sensor" type="imu">
      <always_on>true</always_on>
      <update_rate>100</update_rate>
      <visualize>true</visualize>
      <topic>__default_topic__</topic>
      <plugin filename="libgazebo_ros_imu_sensor.so" name="imu_plugin">
        <topicName>imu/data_raw</topicName>
        <bodyName>imu_link</bodyName>
        <updateRateHZ>10.0</updateRateHZ>
        <gaussianNoise>0.0</gaussianNoise>
        <xyzOffset>0 0 0</xyzOffset>
        <rpyOffset>0 0 0</rpyOffset>
        <frameName>imu_link</frameName>
        <initialOrientationAsReference>false</initialOrientationAsReference>
      </plugin>
      <pose>0 0 0 0 0 0</pose>
    </sensor>
  </gazebo>

  <!-- gazebo_ros_gpu_laser plugin -->
  <gazebo reference="$(arg lidar_link_name)">
    <sensor type="gpu_ray" name="head_hokuyo_sensor">
      <pose>0 0 0 0 0 0</pose>
      <visualize>false</visualize>
      <update_rate>40</update_rate>
      <ray>
        <scan>
          <horizontal>
            <samples>720</samples>
            <resolution>1</resolution>
            <min_angle>-1.570796</min_angle>
            <max_angle>1.570796</max_angle>
          </horizontal>
        </scan>
        <range>
          <min>0.10</min>
          <max>30.0</max>
          <resolution>0.01</resolution>
        </range>
        <noise>
          <type>gaussian</type>
          <!-- Noise parameters based on published spec for Hokuyo laser
               achieving "+-30mm" accuracy at range < 10m.  A mean of 0.0m and
               stddev of 0.01m will put 99.7% of samples within 0.03m of the true
               reading. -->
          <mean>0.0</mean>
          <stddev>0.01</stddev>
        </noise>
      </ray>
      <plugin name="gazebo_ros_head_hokuyo_controller" filename="libgazebo_ros_gpu_laser.so">
        <topicName>/scan</topicName>
        <frameName>base_scan</frameName>
      </plugin>
    </sensor>
  </gazebo>

  <!-- gazebo_ros_camera plugin -->
  <gazebo reference="$(arg camera_link_name)">
    <sensor type="camera" name="camera1">
      <update_rate>30.0</update_rate>
      <camera name="head">
        <horizontal_fov>1.3962634</horizontal_fov>
        <image>
          <width>800</width>
          <height>800</height>
          <format>R8G8B8</format>
        </image>
        <clip>
          <near>0.02</near>
          <far>300</far>
        </clip>
        <noise>
          <type>gaussian</type>
          <!-- Noise is sampled independently per pixel on each frame.
               That pixel's noise value is added to each of its color
               channels, which at that point lie in the range [0,1]. -->
          <mean>0.0</mean>
          <stddev>0.007</stddev>
        </noise>
      </camera>
      <plugin name="camera_controller" filename="libgazebo_ros_camera.so">
        <alwaysOn>true</alwaysOn>
        <updateRate>0.0</updateRate>
        <cameraName>bini/camera1</cameraName>
        <imageTopicName>image_raw</imageTopicName>
        <cameraInfoTopicName>camera_info</cameraInfoTopicName>
        <frameName>camera_link_optical</frameName>
        <!-- setting hackBaseline to anything but 0.0 will cause a misalignment
            between the gazebo sensor image and the frame it is supposed to
            be attached to -->
        <hackBaseline>0.0</hackBaseline>
        <distortionK1>0.0</distortionK1>
            <distortionK2>0.0</distortionK2>
            <distortionK3>0.0</distortionK3>
            <distortionT1>0.0</distortionT1>
            <distortionT2>0.0</distortionT2>
            <CxPrime>0</CxPrime>
            <Cx>0.0</Cx>
            <Cy>0.0</Cy>
            <focalLength>0.0</focalLength>
          </plugin>
        </sensor>
      </gazebo>

    </robot>

What could be the problem?