ROS理论与实践——四、机器人仿真

前言

本文是我在18年深蓝学院上课的第二讲内容,过去两年了,我重新整理了下,并结合当时课程布置的作业,在文中给出。本文主要讲关于rviz仿真和gazebo物理仿真。

一、URDF模型优化

上一讲中详细的介绍了机器人URDF模型的建模过程,如不熟悉,可以翻上一讲的内容。

针对URDF模型存在的这些问题:

  • 模型冗长,重复内容过多;
  • 参数修改麻烦;
  • 没有参数计算的功能

对URDF模型进行了优化,即xacro模型,它的两个优点:

  • 精简了模型代码(通过创建宏定义、文件包含);
  • 提供了可编程的接口(包括常量、变量、数学计算和条件语句)。

1 xacro模型文件使用方法

1.1 常量定义

在xacro文件中对常量进行定义,采用的是property标签,标签里是两个属性,分别是name和value,举例:

<xacro:property name="M_PI" value="3.14159"/>

再比如在原先urdf文件中对于常量定义的修改,代码如下:

<!-- PROPERTY LIST -->
    <xacro:property name="M_PI" value="3.1415926"/>
    <xacro:property name="base_radius" value="0.20"/>
    <xacro:property name="base_length" value="0.16"/>

    <xacro:property name="wheel_radius" value="0.06"/>
    <xacro:property name="wheel_length" value="0.025"/>
    <xacro:property name="wheel_joint_y" value="0.19"/>
    <xacro:property name="wheel_joint_z" value="0.05"/>

    <xacro:property name="caster_radius" value="0.015"/> <!-- wheel_radius - ( base_length/2 - wheel_joint_z) -->
    <xacro:property name="caster_joint_x" value="0.18"/>

常量定义后,使用常量也非常简单,采用${ }的形式,比如:

<origin xyz="0 0 0" rpy="${M_PI/2} 0 0"/>

再比如在urdf模型中对机器人轮模型的优化,代码如下:

 <xacro:macro name="wheel" params="prefix reflect">
        <joint name="${prefix}_wheel_joint" type="continuous">
            <origin xyz="0 ${reflect*wheel_joint_y} ${-wheel_joint_z}" rpy="0 0 0"/>
            <parent link="base_link"/>
            <child link="${prefix}_wheel_link"/>
            <axis xyz="0 1 0"/>
        </joint>

        <link name="${prefix}_wheel_link">
            <visual>
                <origin xyz="0 0 0" rpy="${M_PI/2} 0 0" />
                <geometry>
                    <cylinder radius="${wheel_radius}" length = "${wheel_length}"/>
                </geometry>
                <material name="gray" />
            </visual>
        </link>
    </xacro:macro>

1.2 数学计算

<origin xyz="0 ${(motor_length+wheel_length)/2} 0" rpy="0 0 0"/>

注:在xacro文件进行数学计算时,所有的数学运算都会先转换成浮点数进行,以保证运算的精度。

<xacro:macro name="caster" params="prefix reflect">
        <joint name="${prefix}_caster_joint" type="continuous">
            <origin xyz="${reflect*caster_joint_x} 0 ${-(base_length/2 + caster_radius)}" rpy="0 0 0"/>
            <parent link="base_link"/>
            <child link="${prefix}_caster_link"/>
            <axis xyz="0 1 0"/>
        </joint>

        <link name="${prefix}_caster_link">
            <visual>
                <origin xyz="0 0 0" rpy="0 0 0"/>
                <geometry>
                    <sphere radius="${caster_radius}" />
                </geometry>
                <material name="black" />
            </visual>
        </link>
    </xacro:macro>

1.3 宏定义

类似于C++中函数的使用。

<xacro:macro name="name" params="A B C">
......
</xacro:macro>

宏定义了name后,可进行宏定义的调用,即

<name A="A_value" B="B_value" C="C_value"/>

如上边写轮模型代码中的宏定义,它的宏调用,如下:

 <wheel prefix="left" reflect="-1"/>
 <wheel prefix="right" reflect="1"/>

1.4 文件包含

类似于C和C++中的include。
在xacro文件中,使用include标签下的filename属性,完成文件包含操作。如:

 <xacro:include filename="$(find mbot_description)/urdf/xacro/mbot_base.xacro" />

2 xacro模型文件运行

mbot底盘相当于C++中的main函数,但是还不能直接使用,需要在上层文件中加载,将底盘当作是机器人的零部件。
例如,优化后的xacro模型文件的代码如下:
mbot_base.xacro

<?xml version="1.0"?>
<robot name="mbot" xmlns:xacro="http://www.ros.org/wiki/xacro">

    <!-- PROPERTY LIST -->
    <xacro:property name="M_PI" value="3.1415926"/>
    <xacro:property name="base_radius" value="0.20"/>
    <xacro:property name="base_length" value="0.16"/>

    <xacro:property name="wheel_radius" value="0.06"/>
    <xacro:property name="wheel_length" value="0.025"/>
    <xacro:property name="wheel_joint_y" value="0.19"/>
    <xacro:property name="wheel_joint_z" value="0.05"/>

    <xacro:property name="caster_radius" value="0.015"/> <!-- wheel_radius - ( base_length/2 - wheel_joint_z) -->
    <xacro:property name="caster_joint_x" value="0.18"/>

    <!-- Defining the colors used in this robot -->
    <material name="yellow">
        <color rgba="1 0.4 0 1"/>
    </material>
    <material name="black">
        <color rgba="0 0 0 0.95"/>
    </material>
    <material name="gray">
        <color rgba="0.75 0.75 0.75 1"/>
    </material>
    
    <!-- Macro for robot wheel -->
    <xacro:macro name="wheel" params="prefix reflect">
        <joint name="${prefix}_wheel_joint" type="continuous">
            <origin xyz="0 ${reflect*wheel_joint_y} ${-wheel_joint_z}" rpy="0 0 0"/>
            <parent link="base_link"/>
            <child link="${prefix}_wheel_link"/>
            <axis xyz="0 1 0"/>
        </joint>

        <link name="${prefix}_wheel_link">
            <visual>
                <origin xyz="0 0 0" rpy="${M_PI/2} 0 0" />
                <geometry>
                    <cylinder radius="${wheel_radius}" length = "${wheel_length}"/>
                </geometry>
                <material name="gray" />
            </visual>
        </link>
    </xacro:macro>

    <!-- Macro for robot caster -->
    <xacro:macro name="caster" params="prefix reflect">
        <joint name="${prefix}_caster_joint" type="continuous">
            <origin xyz="${reflect*caster_joint_x} 0 ${-(base_length/2 + caster_radius)}" rpy="0 0 0"/>
            <parent link="base_link"/>
            <child link="${prefix}_caster_link"/>
            <axis xyz="0 1 0"/>
        </joint>

        <link name="${prefix}_caster_link">
            <visual>
                <origin xyz="0 0 0" rpy="0 0 0"/>
                <geometry>
                    <sphere radius="${caster_radius}" />
                </geometry>
                <material name="black" />
            </visual>
        </link>
    </xacro:macro>

    <xacro:macro name="mbot_base">
        <link name="base_footprint">
            <visual>
                <origin xyz="0 0 0" rpy="0 0 0" />
                <geometry>
                    <box size="0.001 0.001 0.001" />
                </geometry>
            </visual>
        </link>

        <joint name="base_footprint_joint" type="fixed">
            <origin xyz="0 0 ${base_length/2 + caster_radius*2}" rpy="0 0 0" />        
            <parent link="base_footprint"/>
            <child link="base_link" />
        </joint>

        <link name="base_link">
            <visual>
                <origin xyz=" 0 0 0" rpy="0 0 0" />
                <geometry>
                    <cylinder length="${base_length}" radius="${base_radius}"/>
                </geometry>
                <material name="yellow" />
            </visual>
        </link>

        <wheel prefix="left" reflect="-1"/>
        <wheel prefix="right" reflect="1"/>

        <caster prefix="front" reflect="-1"/>
        <caster prefix="back" reflect="1"/>
    </xacro:macro>
</robot>

上层文件mbot.xacro

<?xml version="1.0"?>
<robot name="arm" xmlns:xacro="http://www.ros.org/wiki/xacro">

    <xacro:include filename="$(find mbot_description)/urdf/xacro/mbot_base.xacro" />

    <mbot_base/>

</robot>

3 xacro模型显示

主流采用的是直接调用xacro文件解析器,即在launch启动文件中,添加以下代码:

<arg name="model" default="$(find xacro)/xacro --inorder '$(find mbot_description)/urdf/xacro/mbot.xacro'" />
<param name="robot_description" command="$(arg model)" />

其余内容,与之前的launch文件相一致。运行该launch文件即可。

roslaunch mbot_description display_mbot_base_xacro.launch

二、rviz仿真

1 ArbotiX底层控制板

ROS中提供了ArbotiX,是一款控制电机、舵机的硬件控制板,内含一个差速驱动机器人的rviz模拟器。

1.1 安装ArbotiX

本文使用的是ROS版本是Kinetic,因此

git clone https://github.com/vanadiumlabs/arbotix_ros.git
catkin_make

1.2 配置ArbotiX

1.创建launch文件

<launch>
	<arg name="model" default="$(find xacro)/xacro --inorder '$(find mbot_description)/urdf/xacro/mbot_with_camera.xacro'" />
	<arg name="gui" default="false" />

	<param name="robot_description" command="$(arg model)" />

    <!-- 设置GUI参数,显示关节控制插件 -->
	<param name="use_gui" value="$(arg gui)"/>

	<node name="arbotix" pkg="arbotix_python" type="arbotix_driver" output="screen">
        <rosparam file="$(find mbot_description)/config/fake_mbot_arbotix.yaml" command="load" />
        <param name="sim" value="true"/>
    </node>

    <!-- 运行joint_state_publisher节点,发布机器人的关节状态  -->
	<node name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher" />

	<!-- 运行robot_state_publisher节点,发布tf  -->
	<node name="robot_state_publisher" pkg="robot_state_publisher" type="robot_state_publisher" />

    <!-- 运行rviz可视化界面 -->
	<node name="rviz" pkg="rviz" type="rviz" args="-d $(find mbot_description)/config/mbot_arbotix.rviz" required="true" />

</launch>

2.创建配置文件
fake_mbot_arbotix.yaml

controllers: {
   base_controller: {
       type: diff_controller, 
       base_frame_id: base_footprint, 
       base_width: 0.26, 
       ticks_meter: 4100, 
       Kp: 12, 
       Kd: 12, 
       Ki: 0, 
       Ko: 50, 
       accel_limit: 1.0 
    }
}

3.启动仿真器

roslaunch mbot_description arbotix_mbot_with_camera_xacro.launch

4.启动键盘控制

roslaunch mbot_teleop mbot_teleop.launch

在这里插入图片描述

2.实例

将自己创建的机器人URDF模型,改写成xacro形式的模型,并在rviz中显示。然后搭建ArbotiX+rviz仿真环境,将完成的机器人模型放置到rviz中,并通过键盘控制运动。
.xacro文件分为三部分:gazebo.urdf.xacro、smartcar.urdf.xacro、smartcar_body.urdf.xacro。

2.1 模型文件

(1)机器人主体smartcar_body.urdf.xacro文件

  1 <?xml version="1.0"?>  
  2 <robot name="smartcar" xmlns:xacro="http://ros.org/wiki/xacro">  
  3   <property name="M_PI" value="3.14159"/>  
  4  
  5   <!-- Macro for SmartCar body. Including Gazebo extensions, but does not include Kinect -->  
  6   <include filename="$(find smartcar_description)/urdf/gazebo.urdf.xacro"/>  
  7  
  8   <property name="base_x" value="0.33" />  
  9   <property name="base_y" value="0.33" />  
 10  
 11   <xacro:macro name="smartcar_body">  
 12  
 13  
 14     <link name="base_link">  
 15     <inertial>    //惯性属性
 16       <origin xyz="0 0 0.055"/>  
 17       <mass value="1.0" />  
 18       <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>  
 19     </inertial>  
 20     <visual>  
 21       <geometry>  
 22         <box size="0.25 .16 .05"/>  
 23       </geometry>  
 24       <origin rpy="0 0 0" xyz="0 0 0.055"/>  
 25       <material name="blue">  
 26       <color rgba="0 0 .8 1"/>  
 27       </material>  
 28    </visual>  
 29    <collision>   //碰撞属性
 30       <origin rpy="0 0 0" xyz="0 0 0.055"/>  
 31       <geometry>  
 32         <box size="0.25 .16 .05" />  
 33       </geometry>  
 34     </collision>  
 35   </link>  
 36  
 37  
 38  <link name="left_front_wheel">  
 39     <inertial>  
 40       <origin  xyz="0.08 0.08 0.025"/>  
 41       <mass value="0.1" />  
 42        <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>  
 43     </inertial>  
 44     <visual>  
 45       <geometry>  
 46         <cylinder length=".02" radius="0.025"/>  
 47       </geometry>  
 48       <material name="black">  
 49         <color rgba="0 0 0 1"/>  
 50       </material>  
 51     </visual>  
 52     <collision>  
 53       <origin rpy="0 1.57075 1.57075" xyz="0.08 0.08 0.025"/>  
 54       <geometry>  
 55          <cylinder length=".02" radius="0.025"/>  
 56       </geometry>  
 57     </collision>  
 58   </link>  
 59  
 60   <joint name="left_front_wheel_joint" type="continuous">  
 61     <axis xyz="0 0 1"/>  
 62     <parent link="base_link"/>  
 63     <child link="left_front_wheel"/>  
 64     <origin rpy="0 1.57075 1.57075" xyz="0.08 0.08 0.025"/>  
 65     <limit effort="100" velocity="100"/>  
 66     <joint_properties damping="0.0" friction="0.0"/>  
 67   </joint>  
 68  
 69   <link name="right_front_wheel">  
 70     <inertial>  
 71       <origin xyz="0.08 -0.08 0.025"/>  
 72       <mass value="0.1" />  
 73        <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>  
 74     </inertial>  
 75     <visual>  
 76       <geometry>  
 77         <cylinder length=".02" radius="0.025"/>  
 78       </geometry>  
 79       <material name="black">  
 80         <color rgba="0 0 0 1"/>  
 81       </material>  
 82     </visual>  
 83     <collision>  
 84       <origin rpy="0 1.57075 1.57075" xyz="0.08 -0.08 0.025"/>  
 85       <geometry>  
 86          <cylinder length=".02" radius="0.025"/>  
 87       </geometry>  
 88     </collision>  
 89   </link>  
 90  
 91   <joint name="right_front_wheel_joint" type="continuous">  
 92     <axis xyz="0 0 1"/>  
 93     <parent link="base_link"/>  
 94     <child link="right_front_wheel"/>  
 95     <origin rpy="0 1.57075 1.57075" xyz="0.08 -0.08 0.025"/>  
 96     <limit effort="100" velocity="100"/>  
 97     <joint_properties damping="0.0" friction="0.0"/>  
 98  </joint>  
 99  
100  <link name="left_back_wheel">  
101     <inertial>  
102       <origin xyz="-0.08 0.08 0.025"/>  
103       <mass value="0.1" />  
104        <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>  
105     </inertial>  
106     <visual>  
107       <geometry>  
108         <cylinder length=".02" radius="0.025"/>  
109       </geometry>  
110       <material name="black">  
111         <color rgba="0 0 0 1"/>  
112       </material>  
113    </visual>  
114    <collision>  
115        <origin rpy="0 1.57075 1.57075" xyz="-0.08 0.08 0.025"/>  
116       <geometry>  
117          <cylinder length=".02" radius="0.025"/>  
118       </geometry>  
119     </collision>  
120   </link>  
121  
122   <joint name="left_back_wheel_joint" type="continuous">  
123     <axis xyz="0 0 1"/>  
124     <parent link="base_link"/>  
125     <child link="left_back_wheel"/>  
126     <origin rpy="0 1.57075 1.57075" xyz="-0.08 0.08 0.025"/>  
127     <limit effort="100" velocity="100"/>  
128     <joint_properties damping="0.0" friction="0.0"/>  
129   </joint>  
130  
131   <link name="right_back_wheel">  
132     <inertial>  
133        <origin xyz="-0.08 -0.08 0.025"/>  
134        <mass value="0.1" />  
135        <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>  
136     </inertial>  
137     <visual>  
138       <geometry>  
139         <cylinder length=".02" radius="0.025"/>  
140       </geometry>  
141       <material name="black">  
142         <color rgba="0 0 0 1"/>  
143       </material>  
144    </visual>  
145    <collision>  
146       <origin rpy="0 1.57075 1.57075" xyz="-0.08 -0.08 0.025"/>  
147       <geometry>  
148          <cylinder length=".02" radius="0.025"/>  
149       </geometry>  
150     </collision>  
151   </link>  
152  
153  
154   <joint name="right_back_wheel_joint" type="continuous">  
155     <axis xyz="0 0 1"/>  
156     <parent link="base_link"/>  
157     <child link="right_back_wheel"/>  
158     <origin rpy="0 1.57075 1.57075" xyz="-0.08 -0.08 0.025"/>  
159     <limit effort="100" velocity="100"/>  
160     <joint_properties damping="0.0" friction="0.0"/>  
161   </joint>  
162  
163   <link name="head">  
164     <inertial>  
165       <origin xyz="0.08 0 0.08"/>  
166       <mass value="0.1" />  
167       <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>  
168     </inertial>  
169     <visual>  
170       <geometry>  
171         <box size=".02 .03 .03"/>  
172       </geometry>  
173       <material name="white">  
174         <color rgba="1 1 1 1"/>  
175       </material>  
176      </visual>  
177      <collision>  
178       <origin xyz="0.08 0 0.08"/>  
179       <geometry>  
180          <cylinder length=".02" radius="0.025"/>  
181       </geometry>  
182     </collision>  
183   </link>  
184  
185   <joint name="tobox" type="fixed">  
186     <parent link="base_link"/>  
187     <child link="head"/>  
188     <origin xyz="0.08 0 0.08"/>  
189   </joint>  
190   </xacro:macro>  
191  
192 </robot>

(2)gazebo属性部分gazebo.urdf.xacro

  <?xml version="1.0"?>    
   <robot xmlns:controller="http://playerstage.sourceforge.net/gazebo/xmlschema/#controller"   
      xmlns:interface="http://playerstage.sourceforge.net/gazebo/xmlschema/#interface"   
      xmlns:sensor="http://playerstage.sourceforge.net/gazebo/xmlschema/#sensor"   
      xmlns:xacro="http://ros.org/wiki/xacro"   
      name="smartcar_gazebo">  
   
  <!-- ASUS Xtion PRO camera for simulation -->  
 <!-- gazebo_ros_wge100 plugin is in kt2_gazebo_plugins package -->  
 <xacro:macro name="smartcar_sim">  
     <gazebo reference="base_link">  
         <material>Gazebo/Blue</material>  
     </gazebo>  
  
     <gazebo reference="right_front_wheel">  
         <material>Gazebo/FlatBlack</material>  
     </gazebo>  
  
     <gazebo reference="right_back_wheel">  
         <material>Gazebo/FlatBlack</material>  
     </gazebo>  
  
     <gazebo reference="left_front_wheel">  
         <material>Gazebo/FlatBlack</material>  
     </gazebo>  
  
     <gazebo reference="left_back_wheel">  
         <material>Gazebo/FlatBlack</material>  
     </gazebo>  
  
     <gazebo reference="head">  
         <material>Gazebo/White</material>  
     </gazebo>  
 </xacro:macro>  
 </robot>

(3)主文件smartcar.urdf.xacro

 1  <?xml version="1.0"?>
 2 
 3  <robot name="smartcar"  
 4     xmlns:xi="http://www.w3.org/2001/XInclude"
 5     xmlns:gazebo="http://playerstage.sourceforge.net/gazebo/xmlschema/#gz"
 6     xmlns:model="http://playerstage.sourceforge.net/gazebo/xmlschema/#model"
 7     xmlns:sensor="http://playerstage.sourceforge.net/gazebo/xmlschema/#sensor"
 8     xmlns:body="http://playerstage.sourceforge.net/gazebo/xmlschema/#body"
 9     xmlns:geom="http://playerstage.sourceforge.net/gazebo/xmlschema/#geom"
10     xmlns:joint="http://playerstage.sourceforge.net/gazebo/xmlschema/#joint"
11     xmlns:controller="http://playerstage.sourceforge.net/gazebo/xmlschema/#controller"
12 
13     xmlns:interface="http://playerstage.sourceforge.net/gazebo/xmlschema/#interface"
14     xmlns:rendering="http://playerstage.sourceforge.net/gazebo/xmlschema/#rendering"
15     xmlns:renderable="http://playerstage.sourceforge.net/gazebo/xmlschema/#renderable"
16 
17     xmlns:physics="http://playerstage.sourceforge.net/gazebo/xmlschema/#physics"
18     xmlns:xacro="http://ros.org/wiki/xacro">
19 
20   <include filename="$(find smartcar_description)/urdf/smartcar_body.urdf.xacro" />
21 
22   <!-- Body of SmartCar, with plates, standoffs and Create (including sim sensors) -->
23   <smartcar_body/>
24 
25   <smartcar_sim/>
26 
27 </robot>

2.2 设置配置文件

smartcar_arbotix.yaml

1 port: /dev/ttyUSB0
 2 baud: 115200
 3 rate: 20
 4 sync_write: True
 5 sync_read: True
 6 read_rate: 20
 7 write_rate: 20
 8 
 9 controllers: {
10    #  Pololu motors: 1856 cpr = 0.3888105m travel = 4773 ticks per meter (empirical: 4100)
11    base_controller: {type: diff_controller, base_frame_id: base_link, base_width: 0.26, ticks_meter: 4100, Kp: 12, Kd: 12, Ki: 0, Ko: 50, accel_limit: 1.0 }
12 }

2.3 mbot_arbotix.rviz文件

使用第三节使用的mbot_arbotix.rviz文件。

2.4 键盘控制文件smartcar_teleop

添加smartcar_teleop.py文件,代码如下:

#!/usr/bin/env python
import roslib; roslib.load_manifest('smartcar_teleop')
import rospy
from geometry_msgs.msg import Twist
from std_msgs.msg import String
 
class Teleop:
    def __init__(self):
        pub = rospy.Publisher('cmd_vel', Twist)
        rospy.init_node('smartcar_teleop')
        rate = rospy.Rate(rospy.get_param('~hz', 1))
        self.cmd = None
	
        cmd = Twist()
        cmd.linear.x = 0.2
        cmd.linear.y = 0
        cmd.linear.z = 0
        cmd.angular.z = 0
        cmd.angular.z = 0
        cmd.angular.z = 0.5
 
        self.cmd = cmd
        while not rospy.is_shutdown():
            str = "hello world %s" % rospy.get_time()
            rospy.loginfo(str)
            pub.publish(self.cmd)
            rate.sleep()
 
if __name__ == '__main__':Teleop()

2.5 结果展示

实现小车的圆周运动,如下图所示:

在这里插入图片描述

三、Gazebo物理仿真环境搭建

1 配置机器人模型

1.1 添加惯性参数和碰撞属性

在上一节xacro模型中,在标签link附上碰撞属性collision和inertial属性,代码如下:

<xacro:macro name="cylinder_inertial_matrix" params="m r h">
        <inertial>
            <mass value="${m}" />
            <inertia ixx="${m*(3*r*r+h*h)/12}" ixy = "0" ixz = "0"
                iyy="${m*(3*r*r+h*h)/12}" iyz = "0"
                izz="${m*r*r/2}" /> 
        </inertial>
    </xacro:macro>

    <!-- Macro for robot wheel -->
    <xacro:macro name="wheel" params="prefix reflect">
        <joint name="${prefix}_wheel_joint" type="continuous">
            <origin xyz="0 ${reflect*wheel_joint_y} ${-wheel_joint_z}" rpy="0 0 0"/>
            <parent link="base_link"/>
            <child link="${prefix}_wheel_link"/>
            <axis xyz="0 1 0"/>
        </joint>

        <link name="${prefix}_wheel_link">
            <visual>
                <origin xyz="0 0 0" rpy="${M_PI/2} 0 0" />
                <geometry>
                    <cylinder radius="${wheel_radius}" length = "${wheel_length}"/>
                </geometry>
                <material name="gray" />
            </visual>
            <collision>
                <origin xyz="0 0 0" rpy="${M_PI/2} 0 0" />
                <geometry>
                    <cylinder radius="${wheel_radius}" length = "${wheel_length}"/>
                </geometry>
            </collision>
            <cylinder_inertial_matrix  m="${wheel_mass}" r="${wheel_radius}" h="${wheel_length}" />
        </link>

1.2 添加gezebo标签

在link标签前添加gazebo标签。

<gazebo reference="${prefix}_caster_link">
            <material>Gazebo/Black</material>
</gazebo>
<gazebo reference="${prefix}_caster_link">
            <material>Gazebo/Black</material>
</gazebo>
 <gazebo reference="base_link">
            <material>Gazebo/Blue</material>
 </gazebo>
 <gazebo reference="base_footprint">
            <turnGravityOff>false</turnGravityOff>
 </gazebo>

1.3 添加传动装置

给joint添加transmission。

<transmission name="${prefix}_wheel_joint_trans">
            <type>transmission_interface/SimpleTransmission</type>
            <joint name="${prefix}_wheel_joint" >
                <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
            </joint>
            <actuator name="${prefix}_wheel_joint_motor">
                <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
                <mechanicalReduction>1</mechanicalReduction>
            </actuator>
</transmission>

1.4 添加控制器插件

<gazebo>
            <plugin name="differential_drive_controller" 
                    filename="libgazebo_ros_diff_drive.so">
                <rosDebugLevel>Debug</rosDebugLevel>
                <publishWheelTF>true</publishWheelTF>
                <robotNamespace>/</robotNamespace>
                <publishTf>1</publishTf>
                <publishWheelJointState>true</publishWheelJointState>
                <alwaysOn>true</alwaysOn>
                <updateRate>100.0</updateRate>
                <legacyMode>true</legacyMode>
                <leftJoint>left_wheel_joint</leftJoint>
                <rightJoint>right_wheel_joint</rightJoint>
                <wheelSeparation>${wheel_joint_y*2}</wheelSeparation>
                <wheelDiameter>${2*wheel_radius}</wheelDiameter>
                <broadcastTF>1</broadcastTF>
                <wheelTorque>30</wheelTorque>
                <wheelAcceleration>1.8</wheelAcceleration>
                <commandTopic>cmd_vel</commandTopic>
                <odometryFrame>odom</odometryFrame> 
                <odometryTopic>odom</odometryTopic> 
                <robotBaseFrame>base_footprint</robotBaseFrame>
            </plugin>
</gazebo> 

2 创建仿真环境

编辑launch文件,在gazebo中加载新建的机器人模型。
view_mbot_gazebo_empty_world.launch

<launch>

    <!-- 设置launch文件的参数 -->
    <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"/>

    <!-- 运行gazebo仿真环境 -->
    <include file="$(find gazebo_ros)/launch/empty_world.launch">
        <arg name="debug" value="$(arg debug)" />
        <arg name="gui" value="$(arg gui)" />
        <arg name="paused" value="$(arg paused)"/>
        <arg name="use_sim_time" value="$(arg use_sim_time)"/>
        <arg name="headless" value="$(arg headless)"/>
    </include>

    <!-- 加载机器人模型描述参数 -->
    <param name="robot_description" command="$(find xacro)/xacro --inorder '$(find mbot_description)/urdf/xacro/gazebo/mbot_gazebo.xacro'" /> 

    <!-- 运行joint_state_publisher节点,发布机器人的关节状态  -->
    <node name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher" ></node> 

    <!-- 运行robot_state_publisher节点,发布tf  -->
    <node name="robot_state_publisher" pkg="robot_state_publisher" type="robot_state_publisher"  output="screen" >
        <param name="publish_frequency" type="double" value="50.0" />
    </node>

    <!-- 在gazebo中加载机器人模型-->
    <node name="urdf_spawner" pkg="gazebo_ros" type="spawn_model" respawn="false" output="screen"
          args="-urdf -model mrobot -param robot_description"/> 

</launch>

总结