1. 确保已经安装了Rviz

2. 生成并构建ROS功能包

2.1 生成一个catkin工作空间

$ mkdir -p ~/catkin_ws/src
$ cd ~/catkin_ws/src
$ catkin_init_workspace

编译工作空间

$ cd ~/catkin_ws/
$ catkin_make

加载源文件

$ source ~/catkin_ws/devel/setup.bash

在.bashrc文件中加入命令

$ echo "source ~/catkin_ws/devel/setup.bash" >> ~/.bashrc

为了确定源文件是否被加载，通过下列命令查询ROS环境正在使用的工作空间

$ echo $ROS_PACKAGE_PATH

对应输出应为:

home/username/catkin_ws/src:/opt/ros/noetic/share

2.2 漏了一个懒得改

2.3 构建差分驱动的机器人的URDF

URDF是具有特殊定义的XML格式的文件，专门用来对机器人组件级别进行抽象的模型描述。
在ros_robotics功能包目录生成一个/urdf目录：

$ cd ~/catkin_ws/src/robotics
$ mkdir urdf
$ cd urdf

2.3.1 创建机器人底座

机器人的第一个组成部分是底座盒子长宽高分别为0.5,0.5,0.25。
新建文件dd_robot.urdf保存在urdf文件夹下。

<<?xml version='1.0'?>
<robot name="dd_robot">
<!--Base Link-->
    <link  name="base_link">

        <visual>
            <origin xyz="0 0 0 " rpy="0 0 0" />
            <geometry>
                <box size="0.5 0.5 0.25" /> 
                </geometry>
            </visual>
    </link>
</robot>

2.3.2 使用roslaunch

roslaunch：能够简化启动多个ROS节点的过程；简化参数服务器设置的过程
使用时需通过roscore命令来启动节点管理器
roslaunch语法结构

$ roslaunch <package_name> <file.launch>

在ros_robotics功能包里面新建文件夹lacunch，再新建ddrobot_rviz.launch文件

<launch>
    <!-- value passed by command line input-->
    <arg name="model"/>
    <arg name="gui" default="False"/>

    <!-- set these parameters on Parameter Server-->
    <param name="robot_description"
                textfile="$(find ros_robotics)/urdf/$(arg model)"/>
    <param name="use_gui" value="$(arg gui)"/>

    <!-- Start 3 nodes: joint_state_publisher,
                        robot_state_publisher and
                        rviz -->
    <node name="joint_state_publisher"
           pkg="joint_state_publisher"
          type="joint_state_publisher"/>
    <node name="robot_state_publisher"
           pkg="robot_state_publisher"
          type="robot_state_publisher"/>
    <node name="rviz" pkg="rviz" type="rviz"
           args="-d $(find ros_robotics)/urdf.rviz"
           required="true"/>          
</launch>

输入以下命令查看机器人模型

$ roslaunch ros_robotics ddrobot_rviz.launch model:=dd_robot.urdf

如果出现下面错误，RLException: [ddrobot_rviz.launch] is neither a launch file in package [launch] nor is [launch] a launch file name
The traceback for the exception was written to the log file

解决方法：将devel/setup.bash添加到系统

source ./devel/setup.bash

在displays添加Robotmodel和TF，并将FIxed frame改为base_link。

2.3.3 添加轮子

继续在上一段代码加

<?xml version='1.0'?>
<robot name="dd_robot">
<!--Base Link-->
    <link  name="base_link">
        <visual>
            <origin xyz="0 0 0 " rpy="0 0 0" />
            <geometry>
                <box size="0.5 0.5 0.25" /> 
            </geometry>
        </visual>
    </link>

<!-- Right Wheel-->
    <link name="right_wheel">
        <visual>
            <origin xyz="0 0 0" rpy="1.570795 0 0 " />
            <geometry>
                <cylinder length="0.1" radius="0.2"/>
            </geometry>
        </visual>
    </link>
    <joint name="joint_right_wheel" type="continuous">
        <parent link="base_link"/>
        <child link="right_wheel"/>
        <origin xyz="0 -0.30 0" rpy="0 0 0"/>
        <axis xyz="0 1 0"/>
    </joint>

<!-- Left Wheel-->
    <link name="left_wheel">
        <visual>
            <origin xyz="0 0 0" rpy="1.570795 0 0" />
            <geometry>
                <cylinder length="0.1" radius="0.2"/>
            </geometry>
        </visual>
    </link>
    <joint name="joint_left_wheel" type="continuous">
        <parent link="base_link"/>
        <child link="left_wheel"/>
        <origin xyz="0 0.30 0" rpy="0 0 0"/>
        <axis xyz="0 1 0"/>
    </joint>
</robot>

运行

2.3.4 添加颜色

为了方便观看
还是在上面代码改

<?xml version='1.0'?>
<robot name="dd_robot">
<!--Base Link-->
    <link  name="base_link">
        <visual>
            <origin xyz="0 0 0 " rpy="0 0 0" />
            <geometry>
                <box size="0.5 0.5 0.25" /> 
            </geometry>
            <material name="blue">
                <color rgba="0 0.5 1 1"/>
            </material>
        </visual>
    </link>

<!-- Right Wheel-->
    <link name="right_wheel">
        <visual>
            <origin xyz="0 0 0" rpy="1.570795 0 0 " />
            <geometry>
                <cylinder length="0.1" radius="0.2"/>
            </geometry>           
            <material name="black">
                <color rgba="0.05 0.05 0.05 1"/>
            </material>
        </visual>
    </link>
    <joint name="joint_right_wheel" type="continuous">
        <parent link="base_link"/>
        <child link="right_wheel"/>
        <origin xyz="0 -0.30 0" rpy="0 0 0"/>
        <axis xyz="0 1 0"/>
    </joint>

<!-- Left Wheel-->
    <link name="left_wheel">
        <visual>
            <origin xyz="0 0 0" rpy="1.570795 0 0" />
            <geometry>
                <cylinder length="0.1" radius="0.2"/>
            </geometry>
            <material name="black">
                <color rgba="0.05 0.05 0.05 1"/>
            </material>
        </visual>
    </link>
    <joint name="joint_left_wheel" type="continuous">
        <parent link="base_link"/>
        <child link="left_wheel"/>
        <origin xyz="0 0.30 0" rpy="0 0 0"/>
        <axis xyz="0 1 0"/>
    </joint>
</robot>

继续运行，我们的车出来了

2.3.5 添加小脚轮

添加小脚轮来使小车平衡

在base_link加代码

<!--Caster-->
        <visual name="caster">
            <origin xyz="0.2 0 -0.125" rpy="0 0 0"/>
            <geometry>
                <sphere radius="0.05"/>
            </geometry>
        </visual>

2.3.6 添加碰撞属性

添加碰撞属性来使小车检测和识别物体的边界
同样是在<link>元素中加<collision>属性
完整代码

<?xml version='1.0'?>
<robot name="dd_robot">
<!--Base Link-->
    <link  name="base_link">
        <visual>
            <origin xyz="0 0 0 " rpy="0 0 0" />
            <geometry>
                <box size="0.5 0.5 0.25" /> 
            </geometry>
            <material name="blue">
                <color rgba="0 0.5 1 1"/>
            </material>
        </visual>
        <!--Base collision-->
        <collision>
            <origin xyz="0 0 0 " rpy="0 0 0 "/>
            <geometry>
                <box size="0.5 0.5 0.25"/>
            </geometry>    
        </collision>
        <!--Caster-->
        <visual name="caster">
            <origin xyz="0.2 0 -0.125" rpy="0 0 0"/>
            <geometry>
                <sphere radius="0.05"/>
            </geometry>
        </visual>
        <!--caster collision -->
        <collision>
            <origin xyz="0.2 0 -0.125" rpy="0 0 0 "/>
            <geometry>
                <sphere radius="0.05"/>
            </geometry>
        </collision>
    </link>

<!-- Right Wheel-->
    <link name="right_wheel">
        <visual>
            <origin xyz="0 0 0" rpy="1.570795 0 0 " />
            <geometry>
                <cylinder length="0.1" radius="0.2"/>
            </geometry>           
            <material name="black">
                <color rgba="0.05 0.05 0.05 1"/>
            </material>
        </visual>
        <!--right wheel collision -->
        <collision>
            <origin xyz="0 0 0" rpy="1.570795 0 0 "/>
            <geometry>
                <cylinder length="0.1" radius="0.2"/>
            </geometry>
        </collision>
    </link>
    <joint name="joint_right_wheel" type="continuous">
        <parent link="base_link"/>
        <child link="right_wheel"/>
        <origin xyz="0 -0.30 0" rpy="0 0 0"/>
        <axis xyz="0 1 0"/>
    </joint>

<!-- Left Wheel-->
    <link name="left_wheel">
        <visual>
            <origin xyz="0 0 0" rpy="1.570795 0 0" />
            <geometry>
                <cylinder length="0.1" radius="0.2"/>
            </geometry>
            <material name="black">
                <color rgba="0.05 0.05 0.05 1"/>
            </material>
        </visual>
        <!--left wheel collision -->
        <collision>
            <origin xyz="0 0 0" rpy="1.570795 0 0 "/>
            <geometry>
                <cylinder length="0.1" radius="0.2"/>
            </geometry>
        </collision>
    </link>
    <joint name="joint_left_wheel" type="continuous">
        <parent link="base_link"/>
        <child link="left_wheel"/>
        <origin xyz="0 0.30 0" rpy="0 0 0"/>
        <axis xyz="0 1 0"/>
    </joint>
</robot>

2.3.7 移动轮子

接下来，我们通过GUI弹窗来控制轮子的关节组件
将gui添加到命令字段，如下：

$ roslaunch ros_robotics ddrobot_rviz.launch model:=dd_robot.urdf gui:=True

如果发现打开Rviz，发现没有GUI窗口。采用下面这个方法

• 下载joint_state_publisher_gui

$ sudo apt-get install ros-noetic-joint-state-publisher-gui

• 将launch文件里面的joint_state_publisher改为joint_state_publisher_gui
• 重新运行命令，就会出现GUI窗口了
  

2.3.8 添加物理属性

物理属性：包括惯性<inertia>,3*3矩阵；质量<mass>，单位kg
之后就可以在Gazebo引擎中启动了
需要在<link>中添加<inertial>标签
具体代码较长

<?xml version='1.0'?>
<robot name="dd_robot">
<!--Base Link-->
    <link  name="base_link">
        <visual>
            <origin xyz="0 0 0 " rpy="0 0 0" />
            <geometry>
                <box size="0.5 0.5 0.25" /> 
            </geometry>
            <material name="blue">
                <color rgba="0 0.5 1 1"/>
            </material>
        </visual>
        <!--Base collision-->
        <collision>
            <origin xyz="0 0 0 " rpy="0 0 0 "/>
            <geometry>
                <box size="0.5 0.5 0.25"/>
            </geometry>    
        </collision>
        <inertial>
            <mass value="5"/>
            <inertia ixx="0.13" ixy="0.0" ixz="0.0" iyy="0.21" iyz="0.0" izz="0.13"/>
        </inertial>
        <!--Caster-->
        <visual name="caster">
            <origin xyz="0.2 0 -0.125" rpy="0 0 0"/>
            <geometry>
                <sphere radius="0.05"/>
            </geometry>
        </visual>
        <!--caster collision -->
        <collision>
            <origin xyz="0.2 0 -0.125" rpy="0 0 0 "/>
            <geometry>
                <sphere radius="0.05"/>
            </geometry>
        </collision>
        <inertial>
            <mass value="0.5"/>
            <inertia ixx="0.0001" ixy="0.0" ixz="0.0" iyy="0.0001" iyz="0.0" izz="0.0001"/>
        </inertial>
    </link>

<!-- Right Wheel-->
    <link name="right_wheel">
        <visual>
            <origin xyz="0 0 0" rpy="1.570795 0 0 " />
            <geometry>
                <cylinder length="0.1" radius="0.2"/>
            </geometry>           
            <material name="black">
                <color rgba="0.05 0.05 0.05 1"/>
            </material>
        </visual>
        <!--right wheel collision -->
        <collision>
            <origin xyz="0 0 0" rpy="1.570795 0 0 "/>
            <geometry>
                <cylinder length="0.1" radius="0.2"/>
            </geometry>
        </collision>
        <inertial>
            <mass value="0.5"/>
            <inertia ixx="0.01" ixy="0.0" ixz="0.0" iyy="0.005" iyz="0.0" izz="0.005"/>
        </inertial>
    </link>
    <joint name="joint_right_wheel" type="continuous">
        <parent link="base_link"/>
        <child link="right_wheel"/>
        <origin xyz="0 -0.30 0" rpy="0 0 0"/>
        <axis xyz="0 1 0"/>
    </joint>

<!-- Left Wheel-->
    <link name="left_wheel">
        <visual>
            <origin xyz="0 0 0" rpy="1.570795 0 0" />
            <geometry>
                <cylinder length="0.1" radius="0.2"/>
            </geometry>
            <material name="black">
                <color rgba="0.05 0.05 0.05 1"/>
            </material>
        </visual>
        <!--left wheel collision -->
        <collision>
            <origin xyz="0 0 0" rpy="1.570795 0 0 "/>
            <geometry>
                <cylinder length="0.1" radius="0.2"/>
            </geometry>
        </collision>
        <inertial>
            <mass value="0.5"/>
            <inertia ixx="0.01" ixy="0.0" ixz="0.0" iyy="0.005" iyz="0.0" izz="0.005"/>
        </inertial>
    </link>
    <joint name="joint_left_wheel" type="continuous">
        <parent link="base_link"/>
        <child link="left_wheel"/>
        <origin xyz="0 0.30 0" rpy="0 0 0"/>
        <axis xyz="0 1 0"/>
    </joint>
</robot>

我们可以使用check_urdf工具来检查语法

$ check_urdf dd_robot.urdf

2.4 Gazebo

2.4.1 安装Gazebo

打开Gazebo

$ gazebo

2.4.2 使用roslaunch启动Gazebo

$ roslaunch gazebo_ros empty_world.launch

2.4.3 更改颜色

<gazebo reference="base_link">
                material>Gazebo/Blue</material>
                <pose>0 0 3 0 0 0</pose>
            </gazebo>

2.4.4模型验证

验证代码是否有问题

$ gzsdf -p dd_robot.gazebo 

如果这个有问题换下面的

$ gz sdf -p dd_robot.gazebo 

2.4.5 在Gazebo中查看URDF

使用XML生成ddrobot_gazebo.launch

<launch>
  <!-- We resume the logic in gazebo_ros package empty_world.launch, -->
  <!-- changing only the name of the world to be launched -->
  <include file="$(find gazebo_ros)/launch/empty_world.launch">
    <arg name="world_name" value="$(find ros_robotics)/worlds/ddrobot.world"/>
   
    <arg name="paused" default="false"/>
    <arg name="use_sim_time" default="true"/>
    <arg name="gui" default="true"/>
    <arg name="headless" default="false"/>
    <arg name="debug" default="false"/>

  </include>

  <!-- Spawn dd_robot into Gazebo -->
  <node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" output="screen"
     args="-file $(find ros_robotics)/urdf/dd_robot.gazebo -urdf -model ddrobot" />

</launch>

2.4.6 新建环境

在功能包里面新建文件夹worlds
新建文件ddrobot.world

<?xml version="1.0" ?>
<sdf version="1.4">
  <world name="default">
    <include>
      <uri>model://ground_plane</uri>
    </include>
    <include>
      <uri>model://sun</uri>
    </include>
    <include>
      <uri>model://construction_cone</uri>
      <name>construction_cone</name>
      <pose>-3.0 0 0 0 0 0</pose>
    </include>
    <include>
      <uri>model://construction_cone</uri>
      <name>construction_cone</name>
      <pose>3.0 0 0 0 0 0</pose>
    </include>
  </world>
</sdf>

参考文献：ROS机器人开发实用案例分析（第二版）