第二章、配置xacro文件

0.前言

       上一节已经将urdf导出来了，这一节需要配置一下xacro文件。先看一下导出的功能包在gazebo以及rviz中显示的效果。
       将功能包放进工作空间进行编译，source一下环境，先看gazebo:
roslaunch tianracer_description gazebo.launch
        可以看到模型已经加载到gazebo中的empty_world中了，此时模型还是白板，稍后可对颜色进行配置。
        再看rviz,先修改tianracer_description/launch中的 arg name="gui" default="False"改为arg name="gui" default="True"
roslaunch tianracer_description display.launch
此时左侧会出现joint_state_publisher的可视化窗口，拖动上边的动态条即可控制小车的每个关节。

1.添加传动装置

        新建tianracer_description.xacro文件，将urdf文件中的代码复制过来，并对其进行修改。 
<?xml version="1.0" encoding="utf-8"?>
<robot name="tianracer"  xmlns:xacro="http://ros.org/wiki/xacro">

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

<link name="chassis">
    <inertial>
      <origin
        xyz="0.0623235722457065 0.0014584636628485 0.0350371599032402"
        rpy="0 0 0" />
      <mass
        value="5" />
     <inertia ixx="0.010609" ixy="0"          ixz="0"
                          iyy="0.050409"   iyz="0"
                                           izz="0.05865" />
    </inertial>
    <visual>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh filename="package://tianracer_description/meshes/base_link.STL" />
      </geometry>
      <material
        name="">
        <color
          rgba="0.792156862745098 0.819607843137255 0.933333333333333 1" />
      </material>
    </visual>
    <collision>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/base_link.STL" />
      </geometry>
    </collision>
  </link>
  <joint name="base_link_joint" type="fixed">
        <origin xyz="0 0 0" rpy="0 0 0" />        
        <parent link="base_link"/>
        <child link="chassis" />
    </joint>  




  <link
    name="left_steering_hinge">
    <inertial>
      <origin
        xyz="0.00160901052986848 0.00421500740928921 0.000999991873067492"
        rpy="0 0 0" />
      <mass
        value="0.34" />
      <inertia
        ixx="4E-06"
        ixy="0"
        ixz="0"
        iyy="4E-06"
        iyz="0"
        izz="4E-06" />
    </inertial>
    <visual>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/left_steering_hinge.STL" />
      </geometry>
      <material
        name="">
        <color
          rgba="1 1 1 1" />
      </material>
    </visual>
    <collision>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/left_steering_hinge.STL" />
      </geometry>
    </collision>
  </link>



  <joint
    name="left_steering_hinge_joint"
    type="revolute">
    <origin
      xyz="0.1237 0.070647 0.0235"
      rpy="0 0 0" />
    <parent
      link="base_link" />
    <child
      link="left_steering_hinge" />
    <axis
      xyz="0 0 1" />
    <limit
      lower="-0.6"
      upper="0.6"
      effort="10"
      velocity="1000" />
  </joint>



  <link
    name="left_front_wheel">
    <inertial>
      <origin
        xyz="-1.16652756898539E-10 0.000722301233977055 -0.000982991824011559"
        rpy="0 0 0" />
      <mass
        value="0.7" />
     <inertia ixx="0.00026046" ixy="0"          ixz="0"
                            iyy="0.00026046" iyz="0"
                                             izz="0.00041226" />
    </inertial>
    <visual>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/left_front_wheel.STL" />
      </geometry>
      <material
        name="">
        <color
          rgba="0.792156862745098 0.819607843137255 0.933333333333333 1" />
      </material>
    </visual>
    <collision>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/left_front_wheel.STL" />
      </geometry>
    </collision>
  </link>

  <joint
    name="left_front_wheel_joint"
    type="continuous">
    <origin
      xyz="0 0.015649 0"
      rpy="0 0 0" />
    <parent
      link="left_steering_hinge" />
    <child
      link="left_front_wheel" />
    <axis
      xyz="0 1 0" />
  </joint>


  <link
    name="right_steering_hinge">
    <inertial>
      <origin
        xyz="0.00160901052986852 -0.00421500740928916 0.00100000812693248"
        rpy="0 0 0" />
      <mass
        value="0.34" />
      <inertia
         ixx="4E-06"
        ixy="0"
        ixz="0"
        iyy="4E-06"
        iyz="0"
        izz="4E-06" />
    </inertial>
    <visual>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/right_steering_hinge.STL" />
      </geometry>
      <material
        name="">
        <color
          rgba="1 1 1 1" />
      </material>
    </visual>
    <collision>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/right_steering_hinge.STL" />
      </geometry>
    </collision>
  </link>


  <joint
    name="right_steering_hinge_joint"
    type="revolute">
    <origin
      xyz="0.12626 -0.065953 0.0235"
      rpy="0 0 0" />
    <parent
      link="base_link" />
    <child
      link="right_steering_hinge" />
    <axis
      xyz="0 0 1" />
    <limit
      lower="-0.6"
      upper="0.6"
      effort="10"
      velocity="1000" />
  </joint>


  <link
    name="right_front_wheel">
    <inertial>
      <origin
        xyz="1.16652479342783E-10 -0.000722301233976874 -0.000982991824011684"
        rpy="0 0 0" />
      <mass
        value="0.7" />
      <inertia ixx="0.00026046" ixy="0"          ixz="0"
                            iyy="0.00026046" iyz="0"
                                             izz="0.00041226" />
    </inertial>
    <visual>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/right_front_wheel.STL" />
      </geometry>
      <material
        name="">
        <color
          rgba="0.792156862745098 0.819607843137255 0.933333333333333 1" />
      </material>
    </visual>
    <collision>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/right_front_wheel.STL" />
      </geometry>
    </collision>
  </link>


  <joint
    name="right_front_wheel_joint"
    type="continuous">
    <origin
      xyz="0 -0.015649 0"
      rpy="0 0 0" />
    <parent
      link="right_steering_hinge" />
    <child
      link="right_front_wheel" />
    <axis
      xyz="0 1 0" />
  </joint>



  <link
    name="left_rear_wheel">
    <inertial>
      <origin
        xyz="-6.22009417952651E-06 0.000722301233977513 1.58299866985546E-05"
        rpy="0 0 0" />
      <mass
        value="0.7" />
     <inertia ixx="0.00026046" ixy="0"          ixz="0"
                            iyy="0.00026046" iyz="0"
                                             izz="0.00041226" />
    </inertial>
    <visual>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/left_rear_wheel.STL" />
      </geometry>
      <material
        name="">
        <color
          rgba="0.792156862745098 0.819607843137255 0.933333333333333 1" />
      </material>
    </visual>
    <collision>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/left_rear_wheel.STL" />
      </geometry>
    </collision>
  </link>



  <joint
    name="left_rear_wheel_joint"
    type="continuous">
    <origin
      xyz="-0.12626 0.081602 0.0225"
      rpy="0 0 0" />
    <parent
      link="base_link" />
    <child
      link="left_rear_wheel" />
    <axis
      xyz="0 1 0" />
  </joint>




  <link
    name="right_rear_wheel">
    <inertial>
      <origin
        xyz="5.49312575473526E-06 -0.000722301233977277 1.60966959317256E-05"
        rpy="0 0 0" />
      <mass
        value="0.7" />
        <inertia ixx="0.00026046" ixy="0"          ixz="0"
                            iyy="0.00026046" iyz="0"
                                             izz="0.00041226" />
    </inertial>
    <visual>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh  filename="package://tianracer_description/meshes/right_rear_wheel.STL" />
      </geometry>
      <material
        name="">
        <color
          rgba="0.792156862745098 0.819607843137255 0.933333333333333 1" />
      </material>
    </visual>
    <collision>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/right_rear_wheel.STL" />
      </geometry>
    </collision>
  </link>
  <joint
    name="right_rear_wheel_joint"
    type="continuous">
    <origin
      xyz="-0.1237 -0.086296 0.0225"
      rpy="0 0 0" />
    <parent
      link="base_link" />
    <child
      link="right_rear_wheel" />
    <axis
      xyz="0 1 0" />
  </joint>



  <link
    name="lidar">
    <inertial>
      <origin
        xyz="-0.0120919804823413 0.0023160815953297 -0.0191850779635995"
        rpy="0 0 0" />
      <mass
        value="0.0792224121739075" />
      <inertia
        ixx="2.10579541640659E-05"
        ixy="-1.189626176555E-07"
        ixz="4.23690141563745E-07"
        iyy="2.51190032657276E-05"
        iyz="-7.86831091483644E-09"
        izz="4.38241306407012E-05" />
    </inertial>
    <visual>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/lidar.STL" />
      </geometry>
      <material
        name="">
        <color
          rgba="0.792156862745098 0.819607843137255 0.933333333333333 1" />
      </material>
    </visual>
    <collision>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/lidar.STL" />
      </geometry>
    </collision>
  </link>
  <joint
    name="lidar_joint"
    type="fixed">
    <origin
      xyz="0.093603 -8.284E-05 0.12377"
      rpy="0 0 0" />
    <parent
      link="base_link" />
    <child
      link="lidar" />
    <axis
      xyz="0 0 0" />
  </joint>
  <link
    name="camera">
    <inertial>
      <origin
        xyz="-0.00831465204525364 0.000297862545499916 -0.000809694900417546"
        rpy="0 0 0" />
      <mass
        value="0.0203878842392581" />
      <inertia
        ixx="4.0787812214101E-06"
        ixy="-1.28709200468823E-08"
        ixz="-1.65865223773842E-08"
        iyy="3.17565570823081E-06"
        iyz="-1.52713816393124E-08"
        izz="2.98536150732633E-06" />
    </inertial>
    <visual>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/camera.STL" />
      </geometry>
      <material
        name="">
        <color
          rgba="0.43921568627451 0.43921568627451 0.43921568627451 1" />
      </material>
    </visual>
    <collision>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/camera.STL" />
      </geometry>
    </collision>
  </link>
  <joint
    name="camera_joint"
    type="fixed">
    <origin
      xyz="0.14851 0.0022137 0.0975"
      rpy="0 0 0" />
    <parent
      link="base_link" />
    <child
      link="camera" />
    <axis
      xyz="0 0 0" />
  </joint>
  <link
    name="real_sense">
    <inertial>
      <origin
        xyz="-0.00975078931607951 0.00306064913353049 -7.04374991291334E-05"
        rpy="0 0 0" />
      <mass
        value="0.103311749598955" />
      <inertia
        ixx="7.35323632954531E-05"
        ixy="3.0437488683846E-06"
        ixz="2.08538534427428E-08"
        iyy="7.40427481540393E-06"
        iyz="-1.93018760531168E-08"
        izz="7.2832884533889E-05" />
    </inertial>
    <visual>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/real_sense.STL" />
      </geometry>
      <material
        name="">
        <color
          rgba="0.666666666666667 0.698039215686274 0.768627450980392 1" />
      </material>
    </visual>
    <collision>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://tianracer_description/meshes/real_sense.STL" />
      </geometry>
    </collision>
  </link>
  <joint
    name="real_sense_joint"
    type="fixed">
    <origin
      xyz="0.19864 0.0038046 0.052021"
      rpy="0 0 0" />
    <parent
      link="base_link" />
    <child
      link="real_sense" />
    <axis
      xyz="0 0 0" />
  </joint>
上边主要修改的内容是第一句修改为xacro声明： 
<?xml version="1.0" encoding="utf-8"?>
<robot name="tianracer"  xmlns:xacro="http://ros.org/wiki/xacro">

以及一些惯性参数的修改。

        本次项目做的是基于twist消息的阿克曼转向移动机器人，为实现该机器人的运动学，我们给两个后轮以及连接两个前轮的steer添加传动装置。为使用ROS控制驱动机器人，需要在模型中加入transmission元素，将传动装置与joint绑定。

<transmission name="right_steering_hinge_joint_trans">
    <type>transmission_interface/SimpleTransmission</type>
    <joint name="right_steering_hinge_joint" >
      <hardwareInterface>hardware_interface/EffortJointInterface</hardwareInterface>
    </joint>
    <actuator name="right_steering_hinge_joint_motor">
      <hardwareInterface>hardware_interface/EffortJointInterface</hardwareInterface>
      <mechanicalReduction>1</mechanicalReduction>
      <motorTorqueConstant>100</motorTorqueConstant>
    </actuator>
  </transmission>  
  
  <transmission name="left_steering_hinge_joint_trans">
    <type>transmission_interface/SimpleTransmission</type>
    <joint name="left_steering_hinge_joint" >
      <hardwareInterface>hardware_interface/EffortJointInterface</hardwareInterface>
    </joint>
    <actuator name="left_steering_hinge_joint_motor">
      <hardwareInterface>hardware_interface/EffortJointInterface</hardwareInterface>
      <mechanicalReduction>1</mechanicalReduction>
      <motorTorqueConstant>100</motorTorqueConstant>
    </actuator>
  </transmission>


  <transmission name="right_rear_wheel_joint_trans">
    <type>transmission_interface/SimpleTransmission</type>
    <joint name="right_rear_wheel_joint" >
      <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
    </joint>
    <actuator name="right_rear_wheel_joint_motor">
      <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
      <mechanicalReduction>1</mechanicalReduction>
    </actuator>
  </transmission>      
  
  <transmission name="left_rear_wheel_joint_trans">
    <type>transmission_interface/SimpleTransmission</type>
    <joint name="left_rear_wheel_joint" >
      <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
    </joint>
    <actuator name="left_rear_wheel_joint_motor">
      <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
      <mechanicalReduction>1</mechanicalReduction>
    </actuator>
  </transmission>

2.添加插件

       在与tianracer_description.xacro路径相同路径下新建tianracer.gazebo文件

添加gazebo插件

        由于车轮实际上会接触地面，因此会与地面发生物理相互作用，将各个link添加部件材料的附加信息，并且定义各个link的颜色信息。参考

[gazebo官网]    http://gazebosim.org/tutorials/?tut=ros_urdf 

<gazebo reference="chassis">
  <mu1 value="0.0"/>
  <mu2 value="0.0"/>
  <kp  value="10000000.0" />
  <kd  value="1.0" />
  <material>Gazebo/Red</material>
</gazebo>

<gazebo reference="left_steering_hinge">
  <mu1 value="2.0"/>
  <mu2 value="2.0"/>
  <kp  value="10000000.0" />
  <kd  value="1.0" />
  <fdir1 value="1 0 0"/>
  <material>Gazebo/Grey</material>
</gazebo>

<gazebo reference="left_rear_wheel">
  <mu1 value="2.0"/>
  <mu2 value="2.0"/>
  <kp  value="10000000.0" />
  <kd  value="1.0" />
  <fdir1 value="1 0 0"/>
  <material>Gazebo/Black</material>
</gazebo>

<gazebo reference="right_steering_hinge">
  <mu1 value="2.0"/>
  <mu2 value="2.0"/>
  <kp  value="10000000.0" />
  <kd  value="1.0" />
  <fdir1 value="1 0 0"/>
  <material>Gazebo/Grey</material>
</gazebo>

<gazebo reference="right_rear_wheel">
  <mu1 value="2.0"/>
  <mu2 value="2.0"/>
  <kp  value="10000000.0" />
  <kd  value="1.0" />
  <fdir1 value="1 0 0"/>
  <material>Gazebo/Black</material>
</gazebo>

<gazebo reference="left_front_wheel">
  <mu1 value="2.0"/>
  <mu2 value="2.0"/>
  <kp  value="10000000.0" />
  <kd  value="1.0" />
  <fdir1 value="0 0 1"/>
  <material>Gazebo/Black</material>
</gazebo>

<gazebo reference="right_front_wheel">
  <mu1 value="2.0"/>
  <mu2 value="2.0"/>
  <kp  value="10000000.0" />
  <kd  value="1.0" />
  <fdir1 value="0 0 1"/>
  <material>Gazebo/Black</material>
</gazebo>

添加ros_control插件

           由于gazebo并没阿克曼车型的插件，要链接gazebo与ros，我们先添加ros_control插件，它读取所有transmission标记，以及joint_state_publisher插件
<gazebo>
  <plugin name="gazebo_ros_control" filename="libgazebo_ros_control.so">
    <robotNamespace>/tianracer</robotNamespace>
    <robotParam>robot_description</robotParam>
    <robotSimType>gazebo_ros_control/DefaultRobotHWSim</robotSimType>
    <legacyModeNS>true</legacyModeNS>
  </plugin>
</gazebo>

<gazebo>
    <plugin name="joint_state_publisher" filename="libgazebo_ros_joint_state_publisher.so">
      <jointName>left_rear_wheel_joint, right_rear_wheel_joint, left_steering_hinge_joint, right_steering_hinge_joint, right_front_wheel_joint,left_ front_wheel_joint</jointName>
      <updateRate>50.0</updateRate>
      <robotNamespace>/tianracer</robotNamespace>
      <alwaysOn>true</alwaysOn>
    </plugin>
  </gazebo>
添加二维激光雷达插件 
<!-- hokuyo -->
<xacro:unless value="$(optenv DISABLE_GAZEBO_LASER false)">
  <gazebo reference="lidar">
    <material>Gazebo/Grey</material>
    <sensor type="ray" name="hokuyo_sensor">
      <pose>0 0 0.0124 0 0 0</pose>
      <visualize>false</visualize>
      <update_rate>40</update_rate>
      <ray>
        <scan>
          <horizontal>
            <samples>1081</samples>
            <resolution>1</resolution>
            <min_angle>-2.3561944902</min_angle>
            <max_angle>2.3561944902</max_angle>
          </horizontal>
        </scan>
        <range>
          <min>0.1</min>
          <max>10.0</max>
          <resolution>0.01</resolution>
        </range>
        <noise>
          <mean>0.0</mean>
          <stddev>0.01</stddev>
        </noise>
      </ray>
      <plugin name="gazebo_ros_hokuyo_controller" filename="libgazebo_ros_laser.so">
        <topicName>/scan</topicName>
        <frameName>lidar</frameName>
      </plugin>
    </sensor>
  </gazebo>
</xacro:unless>
注意雷达的名字需要与link名对应上。
添加单目摄像头以及深度摄像头插件 
<!-- camera -->
  <gazebo reference="camera">
  <material>Gazebo/Grey</material>
    <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>rrbot/camera1</cameraName>
        <imageTopicName>image_raw</imageTopicName>
        <cameraInfoTopicName>camera_info</cameraInfoTopicName>
        <frameName>camera</frameName>
        <hackBaseline>0.07</hackBaseline>
        <distortionK1>0.0</distortionK1>
        <distortionK2>0.0</distortionK2>
        <distortionK3>0.0</distortionK3>
        <distortionT1>0.0</distortionT1>
        <distortionT2>0.0</distortionT2>
      </plugin>
    </sensor>
    </gazebo>

<gazebo reference="real_sense">
            <sensor type="depth" name="real_sense">
                <always_on>true</always_on>
                <update_rate>20.0</update_rate>
                <camera>
                    <horizontal_fov>${60.0*3.14/180.0}</horizontal_fov>
                    <image>
                        <format>R8G8B8</format>
                        <width>640</width>
                        <height>480</height>
                    </image>
                    <clip>
                        <near>0.05</near>
                        <far>8.0</far>
                    </clip>
                </camera>
                <plugin name="kinect_real_sense_controller" filename="libgazebo_ros_openni_kinect.so">
                    <cameraName>real_sense</cameraName>
                    <alwaysOn>true</alwaysOn>
                    <updateRate>10</updateRate>
                    <imageTopicName>rgb/image_raw</imageTopicName>
                    <depthImageTopicName>depth/image_raw</depthImageTopicName>
                    <pointCloudTopicName>depth/points</pointCloudTopicName>
                    <cameraInfoTopicName>rgb/camera_info</cameraInfoTopicName>
                    <depthImageCameraInfoTopicName>depth/camera_info</depthImageCameraInfoTopicName>
                    <frameName>real_sense</frameName>
                    <baseline>0.1</baseline>
                    <distortion_k1>0.0</distortion_k1>
                    <distortion_k2>0.0</distortion_k2>
                    <distortion_k3>0.0</distortion_k3>
                    <distortion_t1>0.0</distortion_t1>
                    <distortion_t2>0.0</distortion_t2>
                    <pointCloudCutoff>0.4</pointCloudCutoff>
                </plugin>
            </sensor>
        </gazebo>
这里深度摄像头的插件用kinect的插件代替。
最后将tianracer.gazebo添加到tianracer_description.xacro文件里边： 
<xacro:include filename="$(find tianracer_description)/urdf/tianracer.gazebo" />

小结

至此，我们已经配置好小车的各个link的颜色以及传感器的插件，但我们仍无法让小车运动起来，因为我们还未配置小车的controllers。下一节通过配置controllers让小车动起来。

参考资料

1.古月老师的<<ROS机器人开发实践>>

2.从零开始自动驾驶：https://www.bilibili.com/video/BV1ZJ41187tS?spm_id_from=333.999.0.0