URDF_ Xcaro

roscore
rosrun xacro xacro demo01_helloworld.urdf.xacro
rosrun xacro xacro demo01_helloworld.urdf.xacro > demo01_helloworld.urdf from xacro File generation urdf file

Xacro grammar

attribute

Attribute definitions
Calling a
Arithmetic operations

<robot name = "mycar" xmlns:xacro = "http://wiki.ros.org/xacro">
    <!-- 1.  Attribute definitions   The attribute name , The value of the property -->
    <xacro:property name = "PI" value = "3.1415927" />
    <xacro:property name = "radius" value = "0.03" />
    <!-- 2.  Calling a  -->
    <myUsrPropertyxxx name = "${PI}" />
    <myUsrPropertyxxx name = "${radius}" />
    <!-- 3.  Arithmetic operations  -->
    <myUsrPropertyxxx result = "${PI / 2}" />
    <myUsrPropertyxxx result = "${radius * 2}" />
</robot>

macro

Macro definition
Macro call

<robot name="mycar" xmlns:xacro="http://wiki.ros.org/xacro">
    <!-- 1.  Definition of macro   Parameters 1  Parameters 2-->
    <xacro:macro name = "getSum" params = "num1 num2">
        <result value = "${num1 + num2}" />

    </xacro:macro>
    <!-- 2.  Macro call  -->
    <xacro:getSum num1 = "1" num2 = "5" />
</robot>

File contains

<robot name="mycar" xmlns:xacro="http://wiki.ros.org/xacro">
    <!--  The presentation file contains  -->
    <xacro:include filename = "demo02_field.urdf.xacro" />
    <xacro:include filename = "demo03_macro.urdf.xacro" />
</robot>

Xacro example

roslaunch urdf01_rviz demo06_car_base.launch

chassis launch file demo06_car_base.launch

<launch>
    <!-- 1.  Load in the parameter server URDF  It is suggested to use the second way -->
    <!-- <param name = "robot_description" textfile = "$(find urdf01_rviz)/urdf/xacro/demo05_car_base.urdf" /> -->
    <param name = "robot_description" command = "$(find xacro)/xacro $(find urdf01_rviz)/urdf/xacro/demo05_car_base.urdf.xacro" />

    <!-- 2.  start-up rviz -->
    <node pkg = "rviz" type = "rviz" name = "rviz" args = "-d $(find urdf01_rviz)/config/show_mycar.rviz"/>

    <!-- 3.  Add joint status publishing node  -->
    <node pkg = "joint_state_publisher" type = "joint_state_publisher" name = "joint_state_publisher" />

    <!-- 4.  Add robot status publishing node  -->
    <node pkg = "robot_state_publisher" type = "robot_state_publisher" name = "robot_state_publisher" />

    <!-- 5.  Joint motion control node  -->
    <node pkg = "joint_state_publisher_gui" type = "joint_state_publisher_gui" name = "joint_state_publisher_gui" />

</launch>

chassis xacro file demo05_car_base.urdf.xacro

<robot name = "mycar" xmlns:xacro = "http://wiki.ros.org/xacro">
    
    <xacro:property name = "footprint_radius" value = "0.001" />
    <!-- 1.  add to  base_footprint -->
    <link name = "base_footprint">
        <visual>
            <geometry>
                <sphere radius = "${footprint_radius}" />
            </geometry>
        </visual>
    </link>

    <!-- 2.  Add chassis  -->
    <!--  shape :  The chassis is cylindrical , radius  0.1m, high  0.08m  Distance from the ground : 0.015m -->
    <xacro:property name = "base_radius" value = "0.1" />
    <xacro:property name = "base_length" value = "0.08" />
    <xacro:property name = "lidi_space" value = "0.015" />
    <xacro:property name = "base_joint_z" value = "${(base_length) / 2 + lidi_space}" />

    <!-- 2-1 link -->
    <link name = "base_link">
        <visual>
            <geometry>
                <cylinder radius = "0.1" length = "0.08" />
            </geometry>
            <origin xyz = "0 0 0" rpy = "0 0 0"/>
            <material name = "baselink_color">
                <color rgba = "1 0.5 0.2 0.5" />
            </material>
        </visual>
    </link>
    <!-- 2-2 joint  Height of half car body 0.08m/2+0.015m-->
    <joint name = "link2footprint" type = "fixed">
        <parent link = "base_footprint" />
        <child link = "base_link" />
        <!--  The joints z Settings on  =  Height of car body /2 +  Height above ground  -->
        <origin xyz = "0 0 0.055" rpy = "0 0 0" />
    </joint>

    <!-- 3.  Add drive wheels  -->
    <!--  shape :  Cylinder   radius : 0.0325m  length : 0.015m -->

    <!--  attribute  -->
    <xacro:property name = "wheel_radius" value = "0.0325" />
    <xacro:property name = "wheel_length" value = "0.015" />
    <xacro:property name = "PI" value = "3.1415927" />
    <!--  Be careful :  The result is a negative number  -->
    <xacro:property name = "wheel_joint_z" value = "${(base_length / 2 + lidi_space - wheel_radius) * (-1)}" />

    <!-- wheel_name： left or right flag： 1  or  -1 -->
    
    <!--  Macro definition  -->
    <xacro:macro name = "wheel_func" params = "wheel_name flag">
        <!-- 3-1 link -->
        <link name = "${wheel_name}_wheel">
            <visual>
                <geometry>
                    <cylinder radius = "${wheel_radius}" length = "${wheel_length}" />
                </geometry>
                <!--  Under normal circumstances, the cylinder face up , Here the drive wheels are on the left and right , Euler angle needs to be modified , Along the x Shaft rollover 90 degree , about 1.57 radian  -->
                <origin xyz = "0 0 0" rpy = "${PI / 2} 0 0"/>
                <material name = "wheel_color">
                    <color rgba = "0 0 0 0.3" />
                </material>
            </visual>
        </link>

        <!-- 3-2 joint  The joints  -->
        <joint name = "${wheel_name}2link" type = "continuous">
            <parent link = "base_link" />
            <child link = "${wheel_name}_wheel" />
            <!-- x: 0  No offset  y: 0.1  Body radius  z: 0.04 + 0.015 - 0.0325 = 0.055 - 0.0325 = 0.0225, Negative numbers below   Joint height  =  Height of car body  / 2 +  Distance from the ground  -  Wheel radius  -->
            <origin xyz = "0 ${0.1 * flag} ${wheel_joint_z}" rpy = "0 0 0" />
            <!--  Rotate around Y Axis  -->
            <axis xyz = "0 1 0" />
        </joint>
    </xacro:macro>
    <!--  The call takes effect  -->
    <xacro:wheel_func wheel_name = "left" flag = "1" />
    <xacro:wheel_func wheel_name = "right" flag = "-1" />


    <!-- 4.  Add Cardan wheel  -->
    <!--  shape :  The ball   radius : 0.0075m -->

    <!--  attribute  -->
    <xacro:property name = "small_wheel_radius" value = "0.0075" />
    <!--  Joint height :  Height of car body  / 2 +  Distance from the ground  -  Radius of universal wheel  = 0.04 + 0.015 - 0.0075 / 2 = 0.0475 -->
    <xacro:property name = "small_joint_z" value = "${(base_length / 2 + lidi_space - small_wheel_radius) * (-1)}" />

    <!--  macro  -->
    <xacro:macro name = "small_wheel_func" params = "small_wheel_name flag" >
        <!-- 4-1 link -->
        <link name = "${small_wheel_name}_wheel">
            <visual>
                <geometry>
                    <sphere radius = "${small_wheel_radius}" />
                </geometry>
                <origin xyz = "0 0 0" rpy = "0 0 0"/>
                <material name = "wheel_color">
                    <color rbga = "0 0 0 0.3" />
                </material>
            </visual>
        </link>
        
        <!-- 4-2 joint -->
        <joint name = "${small_wheel_name}2link" type = "continuous">
            <parent link = "base_link" />
            <child link = "${small_wheel_name}_wheel" />
            <!-- x: 0.08  Less than the radius  y: 0 z: 0.04 + 0.015 - 0.0075 = 0.0475 -->
            <origin xyz = "${0.08 * flag} 0 ${small_joint_z}" rpy = "0 0 0" />
            <!--  Rotate around Y Axis  -->
            <axis xyz = "0 1 0" />
        </joint>
    </xacro:macro >
    <!--  call  -->
    <xacro:small_wheel_func small_wheel_name = "front" flag = "1" />    
    <xacro:small_wheel_func small_wheel_name = "back" flag = "-1" />    
</robot>

Xacro Practice

On the foundation of the front trolley chassis , Add cameras and radar sensors

camera xacro file demo06_car_camera.urdf.xacro

<robot name="mycar" xmlns:xacro="http://wiki.ros.org/xacro">
    <!--  Camera components  -->
    <!-- 1.  Parameters  -->
    <!--  Parameters :  Connecting rod properties :  The thickness of the (x Direction )、 Width (y Direction )、 Height (z Direction )  Joint attributes : x y z  Offset ,z Offset  =  Half the chassis height + Half the height of the camera  -->
     <xacro:property name = "camera_length" value = "0.02" /> <!--  The thickness of the (x)-->
     <xacro:property name = "camera_width" value = "0.05" /> <!--  Width (y)-->
     <xacro:property name = "camera_height" value = "0.05" /> <!--  Height (z)-->
     <xacro:property name = "joint_camera_x" value = "0.08" /> <!--  The joints (x)-->
     <xacro:property name = "joint_camera_y" value = "0" /> <!--  The joints (y)-->
     <xacro:property name = "joint_camera_z" value = "${base_length / 2 + camera_height / 2}" /> <!--  The joints (z)-->

    <!-- 2.  Design connecting rod joints  -->
    <!-- 2-1 link -->
    <link name = "camera">
        <visual>
            <geometry>
                <box size = "${camera_length} ${camera_width} ${camera_height}" />
            </geometry>
            <material name = "black">
                <color rgba = "0 0 0 0.8" />
            </material>
        </visual>
    </link>
    <!-- 2-2  The joints  -->
    <joint name = "camera2base" type = "fixed">
        <parent link = "base_link" />
        <child link = "camera" />
        <origin xyz = "${joint_camera_x} ${joint_camera_y} ${joint_camera_z}" rpy = "0 0 0" />
    </joint>
</robot>

radar xacro file demo07_car_laser.urdf.xacro

<robot name="mycar" xmlns:xacro="http://wiki.ros.org/xacro">
    <!--  Radar components  -->
    <!--  Parameters  -->
    <!-- 1.  Bracket   Support size :  radius   Height   Joint offset : x y z 2.  radar   Support size :  radius   Height   Joint offset : x y z -->
    <xacro:property name = "support_radius" value = "0.01" />
    <xacro:property name = "support_length" value = "0.15" />
    <xacro:property name = "laser_radius" value = "0.03" />
    <xacro:property name = "laser_length" value = "0.05" />

    <xacro:property name = "joint_support_x" value = "0" />
    <xacro:property name = "joint_support_y" value = "0" />
    <!-- joint1 z =  Height of car body  / 2 +  Support height  / 2 -->
    <xacro:property name = "joint_support_z" value = "${base_length / 2 + support_length / 2}" />

    <xacro:property name = "joint_laser_x" value = "0" />
    <xacro:property name = "joint_laser_y" value = "0" />
    <!-- joint2 z =  Support height  / 2 +  Radar altitude  / 2 -->
    <xacro:property name = "joint_laser_z" value = "${support_length / 2 + laser_length / 2}" />

    <!-- 1.  Bracket  -->
    <link name = "support">
        <visual>
            <geometry>
                <cylinder radius = "${support_radius}" length = "${support_length}" />
            </geometry>
            <material name = "yellow">
                <color rgba = "0.8 0.5 0 0.5" />
            </material>
        </visual>
    </link>
    <joint name = "support2base" type = "fixed"> 
        <parent link = "base_link" />
        <child link = "support" />
        <origin xyz = "${joint_support_x} ${joint_support_y} ${joint_support_z}" rpy = "0 0 0"/>
    </joint>

    <!-- 2.  radar   Fix -->
    <link name = "laser">
        <visual>
            <geometry>
                <cylinder radius = "${laser_radius}" length = "${laser_length}" />
            </geometry>
            <material name = "black">
                <color rgba = "0 0 0 0.5" />
            </material>
        </visual>
    </link>
    <joint name = "laser2support" type = "fixed"> 
        <parent link = "support" />
        <child link = "laser" />
        <origin xyz = "${joint_laser_x} ${joint_laser_y} ${joint_laser_z}" rpy = "0 0 0"/>
    </joint>
</robot>

Combined chassis 、 camera 、 radar xacro file car.urdf.xacro

<robot name="mycar" xmlns:xacro="http://wiki.ros.org/xacro">
    <!--  Including chassis 、 camera 、 Radar xacro file  -->
    <xacro:include filename = "demo05_car_base.urdf.xacro" />
    <xacro:include filename = "demo06_car_camera.urdf.xacro" />
    <xacro:include filename = "demo07_car_laser.urdf.xacro" />
</robot>

launch file car.launch

<launch>
    <!-- 1.  Load in the parameter server URDF  It is suggested to use the second way -->
    <!-- <param name = "robot_description" textfile = "$(find urdf01_rviz)/urdf/xacro/demo05_car_base.urdf" /> -->
    <param name = "robot_description" command = "$(find xacro)/xacro $(find urdf01_rviz)/urdf/xacro/car.urdf.xacro" />

    <!-- 2.  start-up rviz -->
    <node pkg = "rviz" type = "rviz" name = "rviz" args = "-d $(find urdf01_rviz)/config/show_mycar.rviz"/>

    <!-- 3.  Add joint status publishing node  -->
    <node pkg = "joint_state_publisher" type = "joint_state_publisher" name = "joint_state_publisher" />

    <!-- 4.  Add robot status publishing node  -->
    <node pkg = "robot_state_publisher" type = "robot_state_publisher" name = "robot_state_publisher" />

    <!-- 5.  Joint motion control node  -->
    <node pkg = "joint_state_publisher_gui" type = "joint_state_publisher_gui" name = "joint_state_publisher_gui" />

</launch>