请问各位佬，是否可以将一个全向移动的麦轮AGV模型改为差速运动模型？恳请赐教

从网上down了个ridgeback 的gazebo模型，但是这个车的底层是用了四个麦轮，不知道能否将其改为差速的？

我试了下，貌似没有改成功，依然还是全向移动的。下面我贴上原版的xacro代码，烦请指点下应该改那里？

ridgeback.urdf.xacro

<?xml version="1.0"?>
<robot>
  <gazebo>
    <plugin name="gazebo_ros_control" filename="libgazebo_ros_control.so">
      <robotNamespace>/</robotNamespace>
    </plugin>

    <plugin name="ridgeback_ros_force_based_move" filename="libridgeback_ros_force_based_move.so">
      <robotNamespace>/</robotNamespace>
      <commandTopic>cmd_vel</commandTopic>
      <odometryTopic>odom</odometryTopic>
      <odometryFrame>odom</odometryFrame>
      <odometryRate>25.0</odometryRate>
      <robotBaseFrame>base_link</robotBaseFrame>
      <cmdVelTimeOut>0.25</cmdVelTimeOut>
      <!-- Don't publish a transform: the controller does it. -->
      <publishOdometryTf>0</publishOdometryTf>
      <yaw_velocity_p_gain>500.0</yaw_velocity_p_gain>
      <x_velocity_p_gain>10000.0</x_velocity_p_gain>
      <y_velocity_p_gain>10000.0</y_velocity_p_gain>
    </plugin>

    <plugin name="imu_controller" filename="libhector_gazebo_ros_imu.so">
      <robotNamespace>/</robotNamespace>
      <updateRate>50.0</updateRate>
      <bodyName>imu_link</bodyName>
      <topicName>imu/data</topicName>
      <frameId>base_link</frameId>
      <accelDrift>0.005 0.005 0.005</accelDrift>
      <accelGaussianNoise>0.005 0.005 0.005</accelGaussianNoise>
      <rateDrift>0.00005 0.00005 0.00005</rateDrift>
      <rateGaussianNoise>0.00005 0.00005 0.00005</rateGaussianNoise>
      <headingDrift>0.005</headingDrift>
      <headingGaussianNoise>0.005</headingGaussianNoise>
    </plugin>

    <plugin name="gazebo_ros_joint_state_publisher" filename="libgazebo_ros_joint_state_publisher.so">
      <jointName>front_rocker</jointName>
      <robotNamespace>/</robotNamespace>
      <updateRate>50.0</updateRate>
    </plugin>
  </gazebo>

  <!-- All static links get collapsed down to base_link in Gazebo, so that's
       the one to apply the colour to (in Gazebo 5+). -->
  <gazebo reference="base_link">
    <material>Gazebo/DarkGrey</material>
    <gravity>true</gravity>
  </gazebo>

  <!-- Individual link colouring still needed in Gazebo 2.x -->
  <gazebo reference="chassis_link"><material>Gazebo/DarkGrey</material></gazebo>
  <gazebo reference="top_link"><material>Gazebo/DarkGrey</material></gazebo>
  <gazebo reference="left_side_cover_link"><material>Gazebo/Yellow</material></gazebo>
  <gazebo reference="right_side_cover_link"><material>Gazebo/Yellow</material></gazebo>
  <gazebo reference="front_cover_link"><material>Gazebo/DarkGrey</material></gazebo>
  <gazebo reference="rear_cover_link"><material>Gazebo/DarkGrey</material></gazebo>
  <gazebo reference="front_lights_link"><material>Gazebo/White</material></gazebo>
  <gazebo reference="rear_lights_link"><material>Gazebo/Red</material></gazebo>
  <gazebo reference="front_rocker_link"><material>Gazebo/DarkGrey</material></gazebo>
  <gazebo reference="rear_rocker_link"><material>Gazebo/DarkGrey</material></gazebo>
  <gazebo reference="axle_link"><material>Gazebo/DarkGrey</material></gazebo>

  <!-- Wheel friction to zero, as movement is handled by applying forces at
       the body level. -->
  <gazebo reference="front_left_wheel_link">
    <material>Gazebo/DarkGrey</material>
    <mu1>0.0</mu1>
    <mu2>0.0</mu2>
  </gazebo>

  <gazebo reference="front_right_wheel_link">
    <material>Gazebo/DarkGrey</material>
    <mu1>0.0</mu1>
    <mu2>0.0</mu2>
  </gazebo>

  <gazebo reference="rear_left_wheel_link">
    <material>Gazebo/DarkGrey</material>
    <mu1>0.0</mu1>
    <mu2>0.0</mu2>
  </gazebo>

  <gazebo reference="rear_right_wheel_link">
    <material>Gazebo/DarkGrey</material>
    <mu1>0.0</mu1>
    <mu2>0.0</mu2>
  </gazebo>

  <!-- This is an wheel-level solution to possibly revisit at a future date. -->
  <!--<gazebo>
    <plugin name="mecanum_gazebo" filename="libmecanum_force_plugin.so">
      <wheelJointName>front_left_wheel</wheelJointName>
      <forceScaleFactor>1</forceScaleFactor>
    </plugin>
    <plugin name="mecanum_gazebo" filename="libmecanum_force_plugin.so">
      <wheelJointName>front_right_wheel</wheelJointName>
      <forceScaleFactor>-1</forceScaleFactor>
    </plugin>
    <plugin name="mecanum_gazebo" filename="libmecanum_force_plugin.so">
      <wheelJointName>rear_left_wheel</wheelJointName>
      <forceScaleFactor>-1</forceScaleFactor>
    </plugin>
    <plugin name="mecanum_gazebo" filename="libmecanum_force_plugin.so">
      <wheelJointName>rear_right_wheel</wheelJointName>
      <forceScaleFactor>1</forceScaleFactor>
    </plugin>
  </gazebo> -->
</robot>

ridgeback.gazebo

<?xml version="1.0"?>
<robot name="ridgeback" xmlns:xacro="http://ros.org/wiki/xacro">
  <xacro:property name="PI" value="3.1415926535897931" />

  <xacro:property name="wheel_radius" value="0.0759" />
  <xacro:property name="wheel_width" value="0.0790" />

  <xacro:property name="chassis_length" value="0.960" />
  <xacro:property name="chassis_width" value="0.793" />
  <xacro:property name="chassis_height" value="0.216" />
  <xacro:property name="deck_height" value="0.280" />
  <xacro:property name="deck_thickness" value="0.005" />
  <xacro:property name="riser_height" value="$(optenv RIDGEBACK_RISER_HEIGHT 0.055)" />

  <xacro:property name="axle_offset" value="0.0500" />
  <xacro:property name="rocker_offset" value="0.319" />
  <xacro:property name="rocker_width" value="0.472" />

  <xacro:property name="imu_offset_x" value="0.2085" />
  <xacro:property name="imu_offset_y" value="-0.2902" />
  <xacro:property name="imu_offset_z" value="0.1681" />

  <xacro:property name="dummy_inertia" value="1e-09"/>

  <material name="dark_grey"><color rgba="0.2 0.2 0.2 1.0" /></material>
  <material name="light_grey"><color rgba="0.4 0.4 0.4 1.0" /></material>
  <material name="red"><color rgba="0.8 0.0 0.0 1.0" /></material>
  <material name="white"><color rgba="0.9 0.9 0.9 1.0" /></material>
  <material name="yellow"><color rgba="0.8 0.8 0.0 1.0" /></material>
  <material name="black"><color rgba="0.15 0.15 0.15 1.0" /></material>

  <xacro:macro name="wheel" params="prefix side *joint_pose">
    <link name="${prefix}_${side}_wheel_link">
      <visual>
        <origin xyz="0 0 0" rpy="${PI/2} 0 0"/>
        <geometry>
          <mesh filename="package://ridgeback_description/meshes/wheel.stl"/>
        </geometry>
        <material name="black" />
      </visual>
      <collision>
        <origin xyz="0 0 0" rpy="${PI/2} 0 0"/>
        <geometry>
          <cylinder radius="${wheel_radius}" length="${wheel_width}"/>
        </geometry>
      </collision>
      <inertial>
        <origin xyz="0 0 0" rpy="0 0 0"/>
        <mass value="2.3"/>
        <inertia
          ixx="3.3212e-3" ixy="0" ixz="0"
          iyy="6.6424e-3" iyz="0"
          izz="3.3212e-3"/>
      </inertial>
    </link>

    <joint name="${prefix}_${side}_wheel" type="continuous">
      <parent link="${prefix}_rocker_link"/>
      <child link="${prefix}_${side}_wheel_link" />
      <xacro:insert_block name="joint_pose" />
      <axis xyz="0 1 0" />
    </joint>

    <transmission name="${prefix}_wheel_trans">
      <type>transmission_interface/SimpleTransmission</type>
      <joint name="${prefix}_${side}_wheel">
        <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
      </joint>
      <actuator name="${prefix}_${side}_actuator">
        <mechanicalReduction>1</mechanicalReduction>
      </actuator>
    </transmission>
  </xacro:macro>


  <xacro:macro name="rocker" params="prefix joint_type location *joint_limits">
    <link name="${prefix}_rocker_link">
      <visual>
        <origin xyz="0 0 0" rpy="${PI/2} 0 ${PI/2}" />
        <geometry>
          <mesh filename="package://ridgeback_description/meshes/rocker.stl"/>
        </geometry>
        <material name="black" />
      </visual>
      <inertial>
        <origin xyz="0 0 0" rpy="${PI/2} 0 ${PI/2}"/>
        <mass value="10.267"/>
        <inertia
          ixx="0.0288" ixy="2.20484e-6" ixz="-1.3145e-5"
          iyy="0.4324" iyz="1.8944e-3"
          izz="0.4130"/>
      </inertial>
    </link>

    <joint name="${prefix}_rocker" type="${joint_type}">
      <parent link="axle_link"/>
      <child link="${prefix}_rocker_link" />
      <origin xyz="${location*rocker_offset} 0 0" rpy="0 0 0" />
      <axis xyz="1 0 0" />
      <xacro:insert_block name="joint_limits" />
    </joint>

    <xacro:wheel prefix="${prefix}" side="left">
      <origin xyz="0 ${rocker_width/2 + wheel_width/2} 0" rpy="0 0 0" />
    </xacro:wheel>
    <xacro:wheel prefix="${prefix}" side="right">
      <origin xyz="0 ${-(rocker_width/2 + wheel_width/2)} 0" rpy="0 0 0" />
    </xacro:wheel>
  </xacro:macro>

  <xacro:rocker prefix="front" joint_type="revolute" location="1" >
    <limit lower="-0.08726" upper="0.08726" effort="0" velocity="0" />
  </xacro:rocker>

  <xacro:rocker prefix="rear" joint_type="fixed" location="-1" >
    <limit effort="0" velocity="0" />
  </xacro:rocker>

  <link name="base_link"></link>

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

  <link name="chassis_link">
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
        <mesh filename="package://ridgeback_description/meshes/body.stl"/>
      </geometry>
      <material name="black" />
    </visual>
    <collision>
      <origin xyz="0 0 0"/>
      <geometry>
        <mesh filename="package://ridgeback_description/meshes/body-collision.stl"/>
      </geometry>
    </collision>
    <inertial>
      <origin xyz="0.012 0.002 0.067" rpy="${PI/2} 0 ${PI/2}"/>
      <mass value="165.304"/>
      <inertia
        ixx="4.4744" ixy="0.03098" ixz="0.003647"
        iyy="7.1624" iyz="0.1228"
        izz="4.6155"/>
    </inertial>
  </link>

  <link name="riser_link">
    <visual>
      <origin xyz="0 0 ${riser_height/2}" rpy="0 0 ${pi/4}" />
      <geometry>
        <box size="0.493 0.493 ${riser_height}" />
      </geometry>
      <material name="light_grey" />
    </visual>
    <collision>
      <origin xyz="0 0 ${riser_height/2}" rpy="0 0 ${pi/4}" />
      <geometry>
        <box size="0.493 0.493 ${riser_height}" />
      </geometry>
    </collision>
  </link>
  <joint name="riser_link_joint" type="fixed">
    <origin xyz="0 0 ${0.225 - deck_thickness}" rpy="0 0 0" />
    <parent link="chassis_link" />
    <child link="riser_link" />
  </joint>

  <joint name="right_side_cover_link_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 0 0" />
    <parent link="chassis_link"/>
    <child link="right_side_cover_link" />
  </joint>
  <joint name="left_side_cover_link_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 0 0" />
    <parent link="chassis_link"/>
    <child link="left_side_cover_link" />
  </joint>

  <link name="left_side_cover_link">
    <visual>
      <origin xyz="0 0 0" rpy="0 0 ${PI}" />
      <geometry>
        <mesh filename="package://ridgeback_description/meshes/side-cover.stl"/>
      </geometry>
      <material name="yellow" />
    </visual>
  </link>
  <link name="right_side_cover_link">
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
        <mesh filename="package://ridgeback_description/meshes/side-cover.stl"/>
      </geometry>
      <material name="yellow" />
    </visual>
  </link>

  <joint name="front_cover_link_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 0 0" />
    <parent link="chassis_link"/>
    <child link="front_cover_link" />
  </joint>

  <link name="front_cover_link">
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
        <mesh filename="package://ridgeback_description/meshes/end-cover.stl" />
      </geometry>
      <material name="black" />
    </visual>
  </link>

  <joint name="rear_cover_link_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 0 0" />
    <parent link="chassis_link"/>
    <child link="rear_cover_link" />
  </joint>

  <link name="rear_cover_link">
    <visual>
      <origin xyz="0 0 0" rpy="0 0 ${PI}" />
      <geometry>
        <mesh filename="package://ridgeback_description/meshes/end-cover.stl" />
      </geometry>
      <material name="black" />
    </visual>
  </link>

  <joint name="front_lights_link_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 0 0" />
    <parent link="chassis_link"/>
    <child link="front_lights_link" />
  </joint>
  <joint name="rear_lights_link_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 0 0" />
    <parent link="chassis_link"/>
    <child link="rear_lights_link" />
  </joint>

  <link name="front_lights_link">
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
        <mesh filename="package://ridgeback_description/meshes/lights.stl" />
      </geometry>
      <material name="white" />
    </visual>
  </link>
  <link name="rear_lights_link">
    <visual>
      <origin xyz="0 0 0" rpy="0 0 ${PI}" />
      <geometry>
        <mesh filename="package://ridgeback_description/meshes/lights.stl" />
      </geometry>
      <material name="black" />
    </visual>
  </link>

  <joint name="top_link_joint" type="fixed">
    <origin xyz="0 0 ${riser_height-deck_height+deck_thickness}" rpy="0 0 0" />
    <parent link="riser_link"/>
    <child link="top_link" />
  </joint>

  <link name="top_link">
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
        <mesh filename="package://ridgeback_description/meshes/top.stl" />
      </geometry>
      <material name="black" />
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
        <mesh filename="package://ridgeback_description/meshes/top.stl"/>
      </geometry>
    </collision>
  </link>

  <joint name="axle_joint" type="fixed">
    <origin xyz="0 0 ${axle_offset}" rpy="0 0 0" />
    <parent link="chassis_link"/>
    <child link="axle_link" />
  </joint>

  <link name="axle_link">
    <visual>
      <origin xyz="0 0 0" rpy="0 ${PI/2} 0" />
      <geometry>
        <mesh filename="package://ridgeback_description/meshes/axle.stl" />
      </geometry>
      <material name="black" />
    </visual>
  </link>

  <link name="imu_link">
    <inertial>
      <mass value="0.001"/>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <inertia ixx="${dummy_inertia}" ixy="0.0" ixz="0.0" iyy="${dummy_inertia}" iyz="0.0" izz="${dummy_inertia}"/>
    </inertial>
  </link>
  <joint name="imu_joint" type="fixed">
    <parent link="chassis_link" />
    <child link="imu_link" />
    <origin xyz="${imu_offset_x} ${imu_offset_y} ${imu_offset_z}" rpy="0 0 0"/>
  </joint>

  <link name="mid_mount" />
  <joint name="mid_mount_joint" type="fixed">
    <parent link="riser_link" />
    <child link="mid_mount" />
    <origin xyz="0 0 ${riser_height + deck_thickness}" rpy="0 0 0"/>
  </joint>

  <!-- Bring in simulation data for Gazebo. -->
  <xacro:include filename="$(find ridgeback_description)/urdf/ridgeback.gazebo" />

  <!-- Optional standard accessories, including their simulation data. The rendering
       of these into the final description is controlled by optenv variables, which
       default each one to off.-->
  <xacro:include filename="$(find ridgeback_description)/urdf/accessories.urdf.xacro" />

  <!-- Optional custom includes. -->
  <xacro:include filename="$(optenv RIDGEBACK_URDF_EXTRAS empty.urdf)" />
</robot>