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[Gazebo Introductory Tutorial] Lecture 3 Static/Dynamic Programming Modeling of SDF Files

2022-08-10 13:53:00 【Born as Zhaoxu】

【Gazebo入门教程】第三讲 SDFfile static/Dynamic programming modeling

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文章目录

【Gazebo入门教程】第三讲 SDFfile static/Dynamic programming modeling
总结

一、Customize the model and importGazebo

内容简介：This section takes a two-wheeled mobile robot as an example,Movement using a differential drive mechanism,从无到有,使用SDFFinished modeling and inGazeboto complete the simulation,The emphasis is on mastering how to use it through the careful process of modelingSDF文件和GazeboThe software completes the robot simulation.

1. Preparation for basic operations

注意：GazeboThe model file has strict requirements,Specific rules can be found hereSDF格式

$\qquad$ ① 创建模型目录

mkdir -p ~/.gazebo/models/my_robot

$\qquad$ ② 创建模型配置文件

gedit ~/.gazebo/models/my_robot/model.config

$\qquad$ 元数据（config）内容如下：

	<?xml version="1.0"?>
	<model>
	  <name>My Robot</name>
	  <version>1.0</version>
	  <sdf version='1.4'>model.sdf</sdf>
	
	  <author>
	   <name>My Name</name>
	   <email>[email protected]</email>
	  </author>
	
	  <description>
	    My awesome robot.
	  </description>
	</model>

$\qquad$ ② 创建模型配置文件

gedit ~/.gazebo/models/my_robot/model.sdf

$\qquad$ Required marking（sdf）内容如下：

	<?xml version='1.0'?>
	<sdf version='1.4'>
	  <model name="my_robot">
	  </model>
	</sdf>

2. Build model base parts（静态）

基本要求：The content of this section is mainly to create the parts of the robot individually,For example the base、轮子等,Links such as related joint links are not involved,The point is to align the components,So the model is static,Ignore physical effects.

$\qquad$ ① Make the robot model static

注意：在staticwill be after the labellinkGenerate corresponding parts under the label,通过collision的name隔开,Therefore, part of it will be ignored in the post-code display,请自行补充

	<?xml version='1.0'?>
	<sdf version='1.4'>
	  <model name="my_robot">
	  <static>true</static>
	  </model>
	</sdf>

$\qquad$ ② Create the base of the box

代码解释：
box 标签,Used to generate cuboids of the corresponding size
collision 标签,Specifies the collision size
visual 标签,Specifies visual dimensions,Commonly used with collision相同

<?xml version='1.0'?>
<sdf version='1.4'>
  <model name="my_robot">
  <static>true</static>
    <link name='chassis'>
      <pose>0 0 .1 0 0 0</pose>

      <collision name='collision'>
        <geometry>
          <box>
            <size>.4 .2 .1</size>
          </box>
        </geometry>
      </collision>

      <visual name='visual'>
        <geometry>
          <box>
            <size>.4 .2 .1</size>
          </box>
        </geometry>
      </visual>
    </link>
  </model>
</sdf>

$\qquad$ ③ Create casters（万向轮）

注意：The casters are fixed to the base,So both belong to the samelink

<collision name='caster_collision'>
        <pose>-0.15 0 -0.05 0 0 0</pose>
        <geometry>
            <sphere>
            <radius>.05</radius>
          </sphere>
        </geometry>

        <surface>
          <friction>
            <ode>
              <mu>0</mu>
              <mu2>0</mu2>
              <slip1>1.0</slip1>
              <slip2>1.0</slip2>
            </ode>
          </friction>
        </surface>
      </collision>

      <visual name='caster_visual'>
        <pose>-0.15 0 -0.05 0 0 0</pose>
        <geometry>
          <sphere>
            <radius>.05</radius>
          </sphere>
        </geometry>
      </visual>
    </link>

$\qquad$ ④ Create the front and rear wheels

注意：New front and rear wheels were created separatelylink

	  <link name="left_wheel">
      <pose>0.1 0.13 0.1 0 1.5707 1.5707</pose>

      <collision name="collision">
        <geometry>
          <cylinder>
            <radius>.1</radius>
            <length>.05</length>
          </cylinder>
        </geometry>
      </collision>

      <visual name="visual">
        <geometry>
          <cylinder>
            <radius>.1</radius>
            <length>.05</length>
          </cylinder>
        </geometry>
      </visual>
    </link>

    <link name="right_wheel">
      <pose>0.1 -0.13 0.1 0 1.5707 1.5707</pose>

      <collision name="collision">
        <geometry>
          <cylinder>
            <radius>.1</radius>
            <length>.05</length>
          </cylinder>
        </geometry>
      </collision>

      <visual name="visual">
        <geometry>
          <cylinder>
            <radius>.1</radius>
            <length>.05</length>
          </cylinder>
        </geometry>
      </visual>
    </link>

$\qquad$ ⑤ 导入Gazebo可视化模型

使用INSERTImport the model in the corresponding folder,The model can be seen as follows：

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注意：修改SDF文件后,Just delete the original model and re-insert it to update the model

3. Create jointed parts（动态）

基本要求：将static设为false,Add hinge joints for the left and right wheels,joint aroundY轴旋转,Attach each wheel to the chassis

	<static>false</static>

	<joint type="revolute" name="left_wheel_hinge">
      <pose>0 0 -0.03 0 0 0</pose>
      <child>left_wheel</child>
      <parent>chassis</parent>
      <axis>
        <xyz>0 1 0</xyz>
      </axis>
    </joint>

    <joint type="revolute" name="right_wheel_hinge">
      <pose>0 0 0.03 0 0 0</pose>
      <child>right_wheel</child>
      <parent>chassis</parent>
      <axis>
        <xyz>0 1 0</xyz>
      </axis>
    </joint>

4. GazeboBasic emulation

基本操作：启动Gazebo,Insert the latest model,Open the hidden right panel,Select the model you want to control,As shown belowForceThe joint forces below are modified,The robot will move：

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二、创建Velodyne HDL-32 LiDAR传感器

内容简介：This section takes a two-wheeled mobile robot as an example,Movement using a differential drive mechanism,从无到有,使用SDFFinished modeling and inGazeboto complete the simulation,The emphasis is on mastering how to use it through the careful process of modelingSDF文件和GazeboThe software completes the robot simulation.

1. Create the base world

创建新的.world文件：

	gedit velodyne.world

The environment in which the world is created：ground and light

<?xml version="1.0" ?>
<sdf version="1.5">
  <world name="default">

    <!-- A global light source -->
    <include>
      <uri>model://sun</uri>
    </include>

    <!-- A ground plane -->
    <include>
      <uri>model://ground_plane</uri>
    </include>
  </world>
</sdf>

2. Create a static model of the sensor

Sensor base part2D绘图如下：

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对应代码如下：位于< world >的内部

<model name="velodyne_hdl-32">
  <!-- Give the base link a unique name -->
  <link name="base">

    <!-- Offset the base by half the lenght of the cylinder -->
    <pose>0 0 0.029335 0 0 0</pose>
    <collision name="base_collision">
      <geometry>
        <cylinder>
          <!-- Radius and length provided by Velodyne -->
          <radius>.04267</radius>
          <length>.05867</length>
        </cylinder>
      </geometry>
    </collision>

    <!-- The visual is mostly a copy of the collision -->
    <visual name="base_visual">
      <geometry>
        <cylinder>
          <radius>.04267</radius>
          <length>.05867</length>
        </cylinder>
      </geometry>
    </visual>
  </link>

  <!-- Give the base link a unique name -->
  <link name="top">

    <!-- Vertically offset the top cylinder by the length of the bottom cylinder and half the length of this cylinder. -->
    <pose>0 0 0.095455 0 0 0</pose>
    <collision name="top_collision">
      <geometry>
        <cylinder>
          <!-- Radius and length provided by Velodyne -->
          <radius>0.04267</radius>
          <length>0.07357</length>
        </cylinder>
      </geometry>
    </collision>

    <!-- The visual is mostly a copy of the collision -->
    <visual name="top_visual">
      <geometry>
        <cylinder>
          <radius>0.04267</radius>
          <length>0.07357</length>
        </cylinder>
      </geometry>
    </visual>
  </link>
</model>

启动Gazebo查看模型：(先cd到文件路径下)

	cd ~/
	gazebo velodyne.world -u

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View collision properties：Right click on the model,view→Collisions

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3. Add model inertia

3.1 View the current inertia value：Right click on the model,选择View->Inertia

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注意：The purple box corresponds to the associated link size,At this point the model has no inertial information,Therefore the size is too large

3.2 Add inertia information：质量设为1.3kg,Add the corresponding mass and inertia matrices

在< link name=“base” >块中添加以下内容：

  <link name="base">
    <pose>0 0 0.029335 0 0 0</pose>
    <inertial>
      <mass>1.2</mass>
      <inertia>
        <ixx>0.001087473</ixx>
        <iyy>0.001087473</iyy>
        <izz>0.001092437</izz>
        <ixy>0</ixy>
        <ixz>0</ixz>
        <iyz>0</iyz>
      </inertia>
    </inertial>

在< link name=“top” >块中添加以下内容：

 <link name="top">
   <pose>0 0 0.095455 0 0 0</pose>
   <inertial>
     <mass>0.1</mass>
     <inertia>
       <ixx>0.000090623</ixx>
       <iyy>0.000090623</iyy>
       <izz>0.000091036</izz>
       <ixy>0</ixy>
       <ixz>0</ixz>
       <iyz>0</iyz>
     </inertia>
   </inertial>

最终效果如下：

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4. 添加关节

4.1 Defines the top rotation joint around the bottom,在< world >最后添加内容如下：

<!-- Each joint must have a unique name -->
<joint type="revolute" name="joint">

  <!-- Position the joint at the bottom of the top link -->
  <pose>0 0 -0.036785 0 0 0</pose>

  <!-- Use the base link as the parent of the joint -->
  <parent>base</parent>

  <!-- Use the top link as the child of the joint -->
  <child>top</child>

  <!-- The axis defines the joint's degree of freedom -->
  <axis>

    <!-- Revolve around the z-axis -->
    <xyz>0 0 1</xyz>

    <!-- Limit refers to the range of motion of the joint -->
    <limit>

      <!-- Use a very large number to indicate a continuous revolution -->
      <lower>-10000000000000000</lower>
      <upper>10000000000000000</upper>
    </limit>
  </axis>
</joint>

4.2 检验效果：

1. 启动Gazebo,Right click on the model,选择View->Joints,View->Transparent

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2. Open the right panel,选择Velodyne模型.使用ForceTabs apply smaller ones to the joints,You can see the joints rotate

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5. 添加传感器

Basic sensor information：

激光传感器,One or more beams can be emitted,The beam produces distance and intensity data,对应SDF文件中的< scan >和< range >,Corresponding to the beam layout respectively、Quantity and properties of bound bundles,其中< scan >中包含< horizontal >和< vertical >两个块.< horizontal >Components define the rays emitted in the horizontal plane,该< vertical >Components define rays emitted in a vertical plane,VelodyneThe sensor needs vertical rays,然后旋转.We model it as a rotating horizontal sector.

Add and set up sensors：(Add the following in the last section of )

<!-- Add a ray sensor, and give it a name -->
<sensor type="ray" name="sensor">

  <!-- Position the ray sensor based on the specification. Also rotate it by 90 degrees around the X-axis so that the <horizontal> rays become vertical -->
  <pose>0 0 -0.004645 1.5707 0 0</pose>

  <!-- Enable visualization to see the rays in the GUI -->
  <visualize>true</visualize>

  <!-- Set the update rate of the sensor -->
  <update_rate>30</update_rate>
  <ray>

  <!-- The scan element contains the horizontal and vertical beams. We are leaving out the vertical beams for this tutorial. -->
  <scan>

    <!-- The horizontal beams -->
    <horizontal>
      <!-- The velodyne has 32 beams(samples) -->
      <samples>32</samples>

      <!-- Resolution is multiplied by samples to determine number of simulated beams vs interpolated beams. See: http://sdformat.org/spec?ver=1.6&elem=sensor#horizontal_resolution -->
      <resolution>1</resolution>

      <!-- Minimum angle in radians -->
      <min_angle>-0.53529248</min_angle>

      <!-- Maximum angle in radians -->
      <max_angle>0.18622663</max_angle>
    </horizontal>
  </scan>

  <!-- Range defines characteristics of an individual beam -->
  <range>

    <!-- Minimum distance of the beam -->
    <min>0.05</min>

    <!-- Maximum distance of the beam -->
    <max>70</max>

    <!-- Linear resolution of the beam -->
    <resolution>0.02</resolution>
  </range>
</ray>
</sensor>

Check out the simulation effect：

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添加高斯噪声：

在< sensor >的子标签< ray >中添加如下代码：

<noise>
     <!-- Use gaussian noise -->
     <type>gaussian</type>
     <mean>0.0</mean>
     <stddev>0.1</stddev>
</noise>

效果如下：

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通过Ctrl+T打开topic visualization查看：

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总结

内容分析：本篇博客主要介绍了在Gazebo中如何使用SDFDo manual programming modeling,通过编写SDF文件,Realize the step-by-step construction of robots from scratch,体会SDFThe syntax of the file is used,And use two specific examples throughout the article,Wheeled trolleys and Velodyne HDL-32 LiDARThe sensor model is studied in depth.

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