ROS程序设计学习笔记（chapter7）

书籍名称：《Learning ROS for RoboticsProgramming - Second Edition》Chapter2

参考链接：https://www.cnblogs.com/jinee/p/5047021.html

1. 一定要记住它使用的是右手坐标系。
x正方向朝左， y正方向向内， z轴正方向朝上
2. 构建树结构， 即写link和joint
 

1.几何模型

<?xml version ="1.0"?>
<robot name = "text1">

  <!--body-->
  <link name = "base_link">
    <visual>
      <geometry>
        <cylinder length = "0.6" radius = "0.2"/>  
        <!--圆柱体 长度0.6 半径0.2-->
      </geometry>
      <material name = "blue">
       <color rgba = "0 0 0.8 1"/>
      </material>
    </visual>
  </link>
<!--right leg-->
  <link name = "right_leg">
    <visual>
      <geometry>
        <box size = "0.6 .2 .1"/>
       <!--六面体长宽高分别为0.6 0.2 0.1-->
      </geometry>
      <material name = "white">
       <color rgba = "1 1 1 1"/>
      </material>
    </visual>  
  </link>

  <joint name = "base_to_right_leg" type = "fixed">
    <parent link = "base_link"/>
    <child link = "right_leg"/> 
  </joint>

</robot>

<geometry>中添加几何体信息

<material>中添加材质 颜色（rgba格式）

2.调整位置，添加另一条腿

<!--right leg-->
  <link name = "right_leg">
    <visual>
      <geometry>
        <box size = "0.6 .2 .1"/>
      </geometry>
      <material name = "white">
       <color rgba = "1 1 1 1"/>
      </material>
      <origin rpy = "0 1.5705 0" xyz = "0 0 -0.3"/>
    </visual>  
  </link>
  <joint name = "base_to_right_leg" type = "fixed">
    <parent link = "base_link"/>
    <child link = "right_leg"/>
    <origin xyz = "0.22 0 0.25"> 
  </joint>

<!--left leg-->
  <link name = "left_leg">
    <visual>
      <geometry>
        <box size = "0.6 .2 .1"/>
      </geometry>
      <material name = "white">
       <color rgba = "1 1 1 1"/>
      </material>
      <origin rpy = "0 1.5705 0" xyz = "-0.22 0 -0.05"/>
    </visual>  
  </link>
  <joint name = "base_to_left_leg" type = "fixed">
    <parent link = "base_link"/>
    <child link = "left_leg"/> 
    <origin xyz = "-0.22 0 0.25">
  </joint>

每个link的参考坐标系都在它的底部，并与关节的参考坐标系正交，为了添加尺寸，需要指定偏移从一个link到它的关节的子link, 这通过添加origin到每个节点解决。
origin表示的是关节相对于父关节的距离和旋转， xyz和rpy（1.5705:90°）

3.添加剩余部位

调整一下，全部代码：

<?xml version ="1.0"?>
<robot name = "text1">

  <!--body-->
  <link name = "base_link">
    <visual>
      <geometry>
        <cylinder length = "0.6" radius = "0.2"/>
      </geometry>
      <material name = "blue">
       <color rgba = "0 0 0.8 1"/>
      </material>
    </visual>
  </link>

<!--right leg-->
  <link name = "right_leg">
    <visual>
      <geometry>
        <box size = "0.6 .2 .1"/>
      </geometry>
      <material name = "white">
       <color rgba = "1 1 1 1"/>
      </material>
      <origin rpy = "0 1.5705 0" xyz = "0 0 -0.3"/>
    </visual>  
  </link>
  <joint name = "base_to_right_leg" type = "fixed">
    <parent link = "base_link"/>
    <child link = "right_leg"/> 
    <origin xyz = "0.22 0 .25"/>
  </joint>

<!--left leg-->
  <link name = "left_leg">
    <visual>
      <geometry>
        <box size = "0.6 .2 .1"/>
      </geometry>
      <material name = "white">
       <color rgba = "1 1 1 1"/>
      </material>
      <origin rpy = "0 1.5705 0" xyz = "0 0 -0.3"/>
    </visual>  
  </link>
  <joint name = "base_to_left_leg" type = "fixed">
    <parent link = "base_link"/>
    <child link = "left_leg"/>
    <origin xyz = "-0.22 0 .25"/> 
  </joint>
<!--head-->
 <link name = "head">
  <visual>
   <geometry>
    <sphere radius = "0.2"/>
   </geometry>
   <material name  = "white"/>
  </visual>
 </link>
 <joint name="base_to_head" type="fixed">
   <parent link="base_link"/>
   <child link="head"/>
   <origin xyz="0 0 0.3"/>
  </joint>
<!--right foot-->
 <link name = "right_foot">
  <visual>
    <geometry>
     <box size = "0.1 .4 .1"/>
    </geometry>
    <material name = "yellow">
     <color rgba = "1 1 0 1"/>
    </material>
  </visual>
 </link>
 <joint name = "leg_to_right_foot" type = "fixed">
  <parent link = "right_leg"/>
  <child link = "right_foot"/>
  <origin xyz = "0 0 -0.65"/>
 </joint>
 <!--left foot--> 
 <link name = "left_foot">
  <visual>
    <geometry>
     <box size = "0.1 .4 .1"/>
    </geometry>
    <material name = "yellow">
     <color rgba = "1 1 0 1"/>
    </material>
  </visual>
 </link>
 <joint name = "leg_to_left_foot" type = "fixed">
  <parent link = "left_leg"/>
  <child link = "left_foot"/>
  <origin xyz = "0 0 -0.65"/>
 </joint>
<!--right foot front wheel-->
 <link name = "right_front_wheel">
  <visual>
   <geometry>
    <cylinder length= "0.08" radius = "0.05"/>
   </geometry>
   <material name = "black">
    <color rgba = "0 0 0 1"/>
   </material>
  </visual>
 </link>
 <joint name  = "right_foot_to_front_wheel" type = "fixed">
  <parent link ="right_foot"/>
  <child link = "right_front_wheel"/>
  <origin xyz = "0 0.14 -0.05" rpy = "0 1.5705 0"/>
 </joint>
<!--right foot back wheel-->
 <link name = "right_back_wheel">
  <visual>
   <geometry>
    <cylinder length= "0.08" radius = "0.05"/>
   </geometry>
   <material name = "black">
    <color rgba = "0 0 0 1"/>
   </material>
  </visual>
 </link>
 <joint name  = "right_foot_to_back_wheel" type = "fixed">
  <parent link ="right_foot"/>
  <child link = "right_back_wheel"/>
  <origin xyz = "0 -0.14 -0.05" rpy =  "0 1.5705 0"/>
 </joint>
<!--left foot front wheel-->
 <link name = "left_front_wheel">
  <visual>
   <geometry>
    <cylinder length= "0.08" radius = "0.05"/>
   </geometry>
   <material name = "black">
    <color rgba = "0 0 0 1"/>
   </material>
  </visual>
 </link>
 <joint name  = "left_foot_to_front_wheel" type = "fixed">
  <parent link ="left_foot"/>
  <child link = "left_front_wheel"/>
  <origin xyz = "0 0.14 -0.05" rpy =  "0 1.5705 0"/>
 </joint>
<!--left foot back wheel-->
 <link name = "left_back_wheel">
  <visual>
   <geometry>
    <cylinder length= "0.08" radius = "0.05"/>
   </geometry>
   <material name = "black">
    <color rgba = "0 0 0 1"/>
   </material>
  </visual>
 </link>
 <joint name  = "left_foot_to_back_wheel" type = "fixed">
  <parent link ="left_foot"/>
  <child link = "left_back_wheel"/>
  <origin xyz = "0 -0.14 -0.05" rpy =  "0 1.5705 0"/>
 </joint>
</robot>

4.添加碰撞collision

碰撞只要将link包裹住就可以了

  <!--body-->
  <link name = "base_link">
    <visual>
      <geometry>
        <cylinder length = "0.6" radius = "0.2"/>
      </geometry>
      <material name = "blue">
       <color rgba = "0 0 0.8 1"/>
      </material>
    </visual>
    <collision>
     <geometry>
      <cylinder length = "0.6" radius = "0.2"/>
     </geometry>
    </collision>
  </link>

5.xacro

使用宏，简化代码，顺便添加inertial

这里使用了三个宏：代码如下(中间代码省略)

<?xml version ="1.0"?>
<robot name = "text1" xmlns:xacro="http://www.ros.org/wiki/xacro">

 <xacro:property name="wheel_length" value="0.08" />
 <xacro:property name="wheel_radius" value="0.05" />
 <xacro:macro name="default_inertial" params="mass">
  <inertial>
   <mass value="${mass}" />
   <inertia ixx="1.0" ixy="0.0" ixz="0.0"
            iyy="1.0" iyz="0.0"
            izz="1.0" />
   </inertial>
 </xacro:macro>
.
.
.
<!--left foot back wheel-->
 <link name = "left_back_wheel">
  <visual>
   <geometry>
    <cylinder length= "${wheel_length}" radius = "${wheel_radius}"/>
   </geometry>
   <material name = "black">
    <color rgba = "0 0 0 1"/>
   </material>
  </visual>
  <collision>
   <geometry>
    <cylinder length= "${wheel_length}" radius = "${wheel_radius}"/>
   </geometry>
  </collision>
  <xacro:default_inertial mass = "1"/>
 </link>
 <joint name  = "left_foot_to_back_wheel" type = "continuous">
  <parent link ="left_foot"/>
  <child link = "left_back_wheel"/>
  <axis xyz = "0 0 1"/>
  <origin xyz = "0 -0.14 -0.05" rpy =  "0 1.5705 0"/>
 </joint>

</robot>

6.让机器人动起来

让机器人走圆

.cpp如下：

#include <string>
#include <ros/ros.h>
#include <sensor_msgs/JointState.h>
#include <tf/transform_broadcaster.h>

int main(int argc, char** argv) {
    ros::init(argc, argv, "state_publisher_text");
    ros::NodeHandle n;
    ros::Publisher joint_pub = n.advertise<sensor_msgs::JointState>("joint_states", 1);
    tf::TransformBroadcaster broadcaster;
    ros::Rate loop_rate(30);

    const double degree = M_PI/180;

    // robot state
    double inc= 0.005,wheel_1_inc= -0.05,wheel_2_inc= -0.05,wheel_3_inc= -0.07,wheel_4_inc= -0.07;
    double angle= 0,base_head = 0,wheel_1= 0,wheel_2= 0,wheel_3= 0,wheel_4= 0;
    // message declarations
    geometry_msgs::TransformStamped odom_trans;
    sensor_msgs::JointState joint_state;
    odom_trans.header.frame_id = "odom";
    odom_trans.child_frame_id = "base_link";

    while (ros::ok()) {
        //update joint_state
        joint_state.header.stamp = ros::Time::now();
        joint_state.name.resize(9);
        joint_state.position.resize(9);
        joint_state.name[0] ="base_to_head";
        joint_state.position[0] = base_head;
        joint_state.name[1] ="base_to_right_leg";
        joint_state.position[1] = 0;
        joint_state.name[2] ="base_to_left_leg";
        joint_state.position[2] = 0;
	    joint_state.name[3] ="right_leg_to_right_foot";
        joint_state.position[3] = 0;
	    joint_state.name[4] ="left_leg_to_left_foot";
        joint_state.position[4] = 0;
	    joint_state.name[5] ="right_foot_to_front_wheel";
        joint_state.position[5] = wheel_1;
	    joint_state.name[6] ="right_foot_to_back_wheel";
        joint_state.position[6] = wheel_2;
	    joint_state.name[7] ="left_foot_to_front_wheel";
        joint_state.position[7] = wheel_3;
	    joint_state.name[8] ="left_foot_to_back_wheel";
        joint_state.position[8] = wheel_4;







        // update transform
        // (moving in a circle with radius)
        odom_trans.header.stamp = ros::Time::now();
        odom_trans.transform.translation.x = cos(angle);
        odom_trans.transform.translation.y = sin(angle);
        odom_trans.transform.translation.z = 0.0;
        odom_trans.transform.rotation = tf::createQuaternionMsgFromYaw(angle);

        //send the joint state and transform
        joint_pub.publish(joint_state);
        broadcaster.sendTransform(odom_trans);


	    // Create new robot state
	
	    base_head += inc;
	    if(base_head< -2.0||base_head> 2.0) base_head *= -1;
	    wheel_1 += wheel_1_inc;
	    if(wheel_1< -2.0||wheel_1> 2.0) wheel_1 *= -1;
	    wheel_2 += wheel_2_inc;
	    if(wheel_2< -2.0||wheel_2> 2.0) wheel_2 *= -1;
	    wheel_3 += wheel_3_inc;
	    if(wheel_3< -2.0||wheel_3> 2.0) wheel_3 *= -1;
	    wheel_4 += wheel_4_inc;
	    if(wheel_4< -2.0||wheel_4> 2.0) wheel_4 *= -1;

	    angle += degree/4;

        // This will adjust as needed per iteration
        loop_rate.sleep();
    }


    return 0;
}

Chapter7部分错误与解决方法：

P275：
问题：$ check_urdf robot1.urdf
Error:   Error document empty.
        at line 72 in /build/buildd/urdfdom 0.2.10+dfsg/urdf_parser/src/model.cpp
ERROR: Model Parsing the xml failed
解决：check_urdf /home/<user_name>/ROS/catkin_ws/src/learning_urdf/urdf/robot.urdf
在.urdf前添加路径

P276：
问题：$ roslaunch ...命令没有3D模型
解决：<?xml version="1.0"?>代码段，在倒数第二行添加
<node name="rviz" pkg="rviz" type="rviz" args="-d $(find urdf_tutorial)/urdf.rviz" />

P277：
问题：<mesh filename = "package://pr2_description/meshes/gripper_v0/l_finger.dae"/>
我将含有.dae的文件夹（meshes）放在"robot1_description"中，相对路径改为<mesh filename = "package://robot1_description/meshes/gripper_v0/l_finger.dae"/>，加载成功。