建模实践1 —— 手写装有kinova机械臂的husky地面无人车的xacro模型

1.在catkin_ws/src下，创建功能包2.添加底盘3.添加base_footprint4.添加前左轮5.添加前右轮6.添加后左轮7.添加后右轮8.添加上底盘9.添加user_rail_link10.添加前保险杠11.添加前保险杠加长12.添加后保险杠13.添加后保险杠加长14.添加顶板15.在顶板前后分别添加坐标系16.检查xacro模型整体结构

1.在catkin_ws/src下，创建功能包

catkin_create_pkg my_description urdf xacro

在功能包中建立urdf、meshes、launch、config这四个文件夹，分别用于存放特定的文件 接下来编写my.urdf文件

2.添加底盘

<?xml version="1.0"?> <robot name="my_robot" xmlns:xacro="http://ros.org/wiki/xacro"> <!--///Base_link///--> <link name="base_link"> <visual> <origin xyz="0 0 0" rpy="0 0 0" /> <geometry> <mesh filename="package://my_description/meshes/base_link.dae" /> </geometry> </visual> </link> </robot>

编写display_my_urdf.launch文件

<launch> <!-- 设置机器人模型路径参数 --> <param name="robot_description" textfile="$(find my_description)/urdf/my.urdf" /> <!-- 运行joint_state_publisher节点，发布机器人的关节状态 --> <node name="joint_state_publisher_gui" pkg="joint_state_publisher_gui" type="joint_state_publisher_gui" /> <!-- 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 marm_description)/config/marm_urdf.rviz" required="true" /> </launch>

编译工作空间后在rviz中查看

roslaunch marm_description display_marm_urdf.launch

3.添加base_footprint

这个link就是上一篇博客中述及的“机器人映射到地面投影的一个坐标系，一般坐标系的原点都位于地面，方便后续做一些导航、建模相关工作”

<!--// Base footprint is on the ground under the robot ///--> <link name="base_footprint"/> <joint name="base_footprint_joint" type="fixed"> <origin xyz="0 0 ${wheel_vertical_offset - wheel_radius}" rpy="0 0 0" /> <parent link="base_link" /> <child link="base_footprint" /> </joint>

在此之前，还需要定义一些husky的属性，包括底盘尺寸、车轮安装位置、车轮参数：

<!--// Base Size //--> <xacro:property name="base_x_size" value="0.98740000" /> <xacro:property name="base_y_size" value="0.57090000" /> <xacro:property name="base_z_size" value="0.24750000" /> <!--// Wheel Mounting Positions --> <xacro:property name="wheelbase" value="0.5120" /> <xacro:property name="track" value="0.5708" /> <xacro:property name="wheel_vertical_offset" value="0.03282" /> <!-- Wheel Properties //--> <xacro:property name="wheel_length" value="0.1143" /> <xacro:property name="wheel_radius" value="0.1651" />

【启动rviz运行时报错】

[ERROR] [1601879476.512976966]: Unable to parse component [${wheel_vertical_offset] to a double (while parsing a vector value) [ERROR] [1601879476.513133986]: Malformed parent origin element for joint [base_footprint_joint] [ERROR] [1601879476.513180875]: joint xml is not initialized correctly [robot_state_publisher-3] process has died [pid 17781, exit code 255, cmd /opt/ros/kinetic/lib/robot_state_publisher/robot_state_publisher __name:=robot_state_publisher __log:=/home/hjs/.ros/log/5d1643cc-06d4-11eb-b10d-3cf862e0843b/robot_state_publisher-3.log]. log file: /home/hjs/.ros/log/5d1643cc-06d4-11eb-b10d-3cf862e0843b/robot_state_publisher-3*.log

无法将分量[$ {wheel_vertical_offset]解析为双精度（解析向量值时） 关节[base_footprint_joint]的父代原始元素格式错误

就是解析不了这句含有数学表达式的代码：

${wheel_vertical_offset - wheel_radius}

然而xacro是支持“使用属性”的啊，暂时还没有找到解决办法，只好计算器计算一下了，有待后续发现是哪里设置错误了；

将${wheel_vertical_offset - wheel_radius}替换为 -0.13228 ，在rviz中查看：

4.添加前左轮

<!-- front_left_wheel_link //--> <link name="front_left_wheel_link"> <visual> <origin xyz="0 0 0" rpy="0 0 0" /> <geometry> <mesh filename="package://my_description/meshes/wheel.dae" /> </geometry> </visual> </link> <joint name="${wheel_prefix}_wheel" type="continuous"> <origin xyz="0.256 0.2854 0.03282" rpy="0 0 0" /> <parent link="base_link"/> <child link="front_left_wheel_link"/> <xacro:insert_block name="joint_pose"/> <axis xyz="0 1 0" rpy="0 0 0" /> </joint>

在rviz中查看：

5.添加前右轮

<!-- front_right_wheel_link //--> <link name="front_right_wheel_link"> <visual> <origin xyz="0 0 0" rpy="0 0 0" /> <geometry> <mesh filename="package://my_description/meshes/wheel.dae" /> </geometry> </visual> </link> <joint name="front_right_wheel" type="continuous"> <origin xyz="0.256 -0.2854 0.03282" rpy="0 0 0" /> <parent link="base_link"/> <child link="front_right_wheel_link"/> <xacro:insert_block name="joint_pose"/> <axis xyz="0 1 0" rpy="0 0 0" /> </joint>

6.添加后左轮

<!-- rear_left_wheel_link //--> <link name="rear_left_wheel_link"> <visual> <origin xyz="0 0 0" rpy="0 0 0" /> <geometry> <mesh filename="package://my_description/meshes/wheel.dae" /> </geometry> </visual> </link> <joint name="rear_left_wheel" type="continuous"> <origin xyz="-0.256 0.2854 0.03282" rpy="0 0 0" /> <parent link="base_link"/> <child link="rear_left_wheel_link"/> <xacro:insert_block name="joint_pose"/> <axis xyz="0 1 0" rpy="0 0 0" /> </joint>

7.添加后右轮

<!-- rear_right_wheel_link //--> <link name="rear_right_wheel_link"> <visual> <origin xyz="0 0 0" rpy="0 0 0" /> <geometry> <mesh filename="package://my_description/meshes/wheel.dae" /> </geometry> </visual> </link> <joint name="rear_right_wheel" type="continuous"> <origin xyz="-0.256 -0.2854 0.03282" rpy="0 0 0" /> <parent link="base_link"/> <child link="rear_right_wheel_link"/> <xacro:insert_block name="joint_pose"/> <axis xyz="0 1 0" rpy="0 0 0" /> </joint>

8.添加上底盘

<!--/ top_chassis_link /--> <link name="top_chassis_link"> <visual> <origin xyz="0 0 0" rpy="0 0 0" /> <geometry> <mesh filename="package://my_description/meshes/top_chassis.dae" /> </geometry> </visual> </link> <joint name="top_chassis_joint" type="fixed"> <parent link="base_link" /> <child link="top_chassis_link" /> </joint>

可见top_chassis_link和base_link的坐标系相同

9.添加user_rail_link

<!--/// user_rail_link --> <link name="user_rail_link"> <visual> <geometry> <mesh filename="package://my_description/meshes/user_rail.dae" /> </geometry> </visual> </link> <joint name="user_rail" type="fixed"> <origin xyz="0.272 0 0.245" rpy="0 0 0" /> <parent link="base_link" /> <child link="user_rail_link" /> </joint>

10.添加前保险杠

<!-- front_bumper_link --> <link name="front_bumper_link"> <visual> <geometry> <mesh filename="package://my_description/meshes/bumper.dae" /> </geometry> </visual> </link> <!-- Attach front bumper --> <joint name="front_bumper" type="fixed"> <origin xyz="0.48 0 0.091" rpy="0 0 0" /> <parent link="base_link" /> <child link="front_bumper_link" /> </joint>

11.添加前保险杠加长

<!--/ front_bumper_extension_link --> <link name="front_bumper_extension_link"> <visual> <geometry> <mesh filename="package://my_description/meshes/bumper_extension.dae" /> </geometry> </visual> </link> <joint name="front_bumper_extension" type="fixed"> <origin xyz="0.48 0 0.091" rpy="0 0 0" /> <parent link="base_link" /> <child link="front_bumper_extension_link" /> </joint>

12.添加后保险杠

<!--/ rear_bumper_link ///--> <link name="rear_bumper_link"> <visual> <geometry> <mesh filename="package://my_description/meshes/bumper.dae" /> </geometry> </visual> </link> <joint name="rear_bumper" type="fixed"> <origin xyz="-0.48 0 0.091" rpy="0 0 3.14159" /> <parent link="base_link" /> <child link="rear_bumper_link" /> </joint>

13.添加后保险杠加长

<!-- // rear_bumper_extension_link /--> <link name="rear_bumper_extension_link"> <visual> <geometry> <mesh filename="package://my_description/meshes/bumper_extension.dae" /> </geometry> </visual> </link> <joint name="rear_bumper_extension" type="fixed"> <origin xyz="-0.48 0 0.091" rpy="0 0 3.14159" /> <parent link="base_link" /> <child link="rear_bumper_extension_link" /> </joint>

14.添加顶板

<!--/ top_plate_link ///--> <link name="top_plate_link"> <visual> <origin xyz="0 0 0" rpy="0 0 0" /> <geometry> <mesh filename="package://my_description/meshes/top_plate.dae" /> </geometry> </visual> </link> <joint name="top_plate_joint" type="fixed"> <parent link="base_link" /> <child link="top_plate_link"/> <origin xyz="0.0812 0 0.245" rpy="0 0 0"/> </joint>

15.在顶板前后分别添加坐标系

<!--/ ///--> <link name="top_plate_front_link"/> <link name="top_plate_rear_link"/> <!-- Top plate front link --> <joint name="top_plate_front_joint" type="fixed"> <parent link="top_plate_link" /> <child link="top_plate_front_link"/> <origin xyz="0.36367 0 0.00639" rpy="0 0 0"/> </joint> <!-- Top plate rear link--> <joint name="top_plate_rear_joint" type="fixed"> <parent link="top_plate_link" /> <child link="top_plate_rear_link"/> <origin xyz="-0.36633 0 0.00639" rpy="0 0 0"/> </joint>

看一下现在的TF树吧！

16.检查xacro模型整体结构

进入xacro文件夹下

urdf_to_graphiz my.urdf.xacro

至此，husky地面无人车终于整理完毕了！通过自己从头到尾建立模型，可以说现在对husky的任何一个joint或者link都了如指掌，将官方的转化为自己的。