MYRAbot's arm model for simulation (urdf+gazebo)

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Creation of URDF model

URDF (Unified Robot Description Format) is the format used to define the model of the arm (xml) in order to simulate it in gazebo. It consists of a tree of geometrical elements (links) plugged through joints(joints). This joints can be fixed or mobile, the mobile joints can be rotating, linear or floating.

First, we will create a new package with the necessary dependences for our programs (urdf brazo_fer std_msgs sensor_msgs tf roscpp). We will execute the next commands in a terminal: 

cd ~/ros_workspace
roscreate-pkg brazo_fer_modelo urdf brazo_fer std_msgs sensor_msgs tf roscpp

We have divided the model in three files, main file, macros file and placement file. For the main file, we will create a file named "brazo.xacro" within the folder "urdf" of the created package with the content that is shown below: 

<?xml version="1.0"?>

<robot>

	<include filename="$(find brazo_fer_modelo)/urdf/brazo-macros.xacro" />

<macro name="brazo" params="parent *origin">

  <joint name="fixed" type="fixed">
    <parent link="${parent}"/>
    <child link="base_brazo_link"/>
    <insert_block name="origin" />
    <axis xyz="0 0 1" />  
  </joint>
    
  <link name="base_brazo_link">
    <visual>
      <geometry>
        <box size="0.032 0.05 0.04"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0 -0.0135 0.020"/>
      <material name="black">
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 -0.0135 0.020"/>		
      <geometry>
        <box size="0.032 0.05 0.04"/>
      </geometry>
    </collision>
    <inertial>
      <origin rpy="0 0 0" xyz="0 -0.0135 0.020"/>			
      <mass value="0.055"/>
	  <default_inertia_servos />
    </inertial>       
  </link>

  <joint name="base" type="revolute">
    <parent link="base_brazo_link"/>
    <child link="hombro_link"/>
    <origin xyz="0 0 0.04" rpy="0 0 0" />
    <axis xyz="0 0 1" />
	<default_limit />
	<default_dynamics />          
  </joint>
  
  <link name="hombro_link">
    <visual>
      <geometry>
        <box size="0.04 0.032 0.05"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0 0 0.025"/>
      <material name="black" />
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 0 0.025"/>		
	  <geometry>
        <box size="0.04 0.032 0.05"/>
      </geometry>       
    </collision> 
    <inertial>
      <origin rpy="0 0 0" xyz="0 0 0.025"/>			
      <mass value="0.055"/>
	  <default_inertia_servos />
    </inertial>        
  </link>  

  <joint name="arti1" type="revolute">
    <parent link="hombro_link"/>
    <child link="brazo_link"/>  
    <origin xyz="0 0 0.0385" rpy="0 0 0" />
	<axis xyz="1 0 0" />
	<default_limit />
	<default_dynamics />        
  </joint>
  
<!--Brazo-->

<servo nombre="brazo" />
  
  <joint name="servo_arti1_B" type="fixed">
    <parent link="brazo_link"/>
    <child link="brazo_link_B"/>  
    <origin xyz="0 0 0" rpy="0 0 0" />
	<axis xyz="1 0 0" />    
  </joint>  

<base nombre="brazo" /> 
  
  <joint name="servo_arti1_D" type="fixed">
    <parent link="brazo_link"/>
    <child link="brazo_link_SI"/>  
    <origin xyz="0 0 0" rpy="0 0 0" />
	<axis xyz="1 0 0" />    
  </joint>  

<soporte nombre="brazo" simetrico="1" lado="I" />  
  
  <joint name="servo_arti1_I" type="fixed">
    <parent link="brazo_link"/>
    <child link="brazo_link_SD"/>  
    <origin xyz="0 0 0" rpy="0 0 0" />
	<axis xyz="1 0 0" />    
  </joint>  
  
<soporte nombre="brazo" simetrico="-1" lado="D" />     
  
  <joint name="arti2" type="revolute">
    <parent link="brazo_link"/>
    <child link="antebrazo_link"/>
    <origin xyz="0 0 0.104" rpy="0 0 0" />
    <axis xyz="1 0 0" />
	<default_limit />
	<default_dynamics />            
  </joint>
  
<!--Antebrazo-->
  
<servo nombre="antebrazo" /> 
  
  <joint name="servo_arti2_B" type="fixed">
    <parent link="antebrazo_link"/>
    <child link="antebrazo_link_B"/>  
    <origin xyz="0 0 0" rpy="0 0 0" />
	<axis xyz="1 0 0" />    
  </joint>  
  
<base nombre="antebrazo" />
  
  <joint name="servo_arti2_D" type="fixed">
    <parent link="antebrazo_link"/>
    <child link="antebrazo_link_SI"/>  
    <origin xyz="0 0 0" rpy="0 0 0" />
	<axis xyz="1 0 0" />    
  </joint>  
  
<soporte nombre="antebrazo" simetrico="1" lado="I" />  
  
  <joint name="servo_arti2_I" type="fixed">
    <parent link="antebrazo_link"/>
    <child link="antebrazo_link_SD"/>  
    <origin xyz="0 0 0" rpy="0 0 0" />
	<axis xyz="1 0 0" />    
  </joint>  
  
<soporte nombre="antebrazo" simetrico="-1" lado="D" />     

  <joint name="arti3" type="revolute">
    <parent link="antebrazo_link"/>
    <child link="muneca_link"/>
    <origin xyz="0 0 0.104" rpy="0 0 0" />
    <axis xyz="1 0 0" />
	<default_limit />
	<default_dynamics />             
  </joint>
  
<!--Muñeca-->
  
  <link name="muneca_link">
    <visual>
      <geometry>
        <box size="0.05 0.04 0.032"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0.00625 0 0.06"/>
      <material name="black" />
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0.00625 0 0.06"/>		
	  <geometry>
        <box size="0.05 0.04 0.032"/>
      </geometry>
    </collision>
    <inertial>
      <origin rpy="0 0 0" xyz="0.00625 0 0.06"/>			
      <mass value="0.055"/>
	  <default_inertia_servos />
    </inertial>            
  </link>  
  
  <joint name="servo_arti3_B" type="fixed">
    <parent link="muneca_link"/>
    <child link="muneca_link_B"/>  
    <origin xyz="0 0 0" rpy="0 0 0" />
	<axis xyz="1 0 0" />    
  </joint>  
  
  <link name="muneca_link_B">    
	<visual>
      <geometry>
        <box size="0.05325 0.04 0.005"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0.004625 0 0.0415"/>
      <material name="white">
		<color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0.004625 0 0.0415"/>		
	  <geometry>
        <box size="0.05325 0.04 0.005"/>
      </geometry>
    </collision>
    <inertial>
      <origin rpy="0 0 0" xyz="0.004625 0 0.0415"/>		
      <mass value="0.0005"/>
	  <default_inertia />
    </inertial>              
  </link>
  
  <joint name="servo_arti3_D" type="fixed">
    <parent link="muneca_link"/>
    <child link="muneca_link_SI"/>  
    <origin xyz="0 0 0" rpy="0 0 0" />
	<axis xyz="1 0 0" />    
  </joint>  
  
  <link name="muneca_link_SI">    
	<visual>
      <geometry>
        <box size="0.002 0.032 0.0555"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0.021 0 0.01625"/>
      <material name="white">
		<color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0.021 0 0.01625"/>		
	  <geometry>
        <box size="0.002 0.032 0.0555"/>
      </geometry>
    </collision>
    <inertial>
      <origin rpy="0 0 0" xyz="0.021 0 0.01625"/>		
      <mass value="0.0005"/>
	  <default_inertia />
    </inertial>           
  </link>
  
  <joint name="servo_arti3_I" type="fixed">
    <parent link="muneca_link"/>
    <child link="muneca_link_SD"/>  
    <origin xyz="0 0 0" rpy="0 0 0" />
	<axis xyz="1 0 0" />    
  </joint>  
  
  <link name="muneca_link_SD">    
	<visual>
      <geometry>
        <box size="0.002 0.032 0.0555"/>
      </geometry>
      <origin rpy="0 0 0" xyz="-0.021 0 0.01625"/>
      <material name="white">
		<color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="-0.021 0 0.01625"/>		
	  <geometry>
        <box size="0.002 0.032 0.0555"/>
      </geometry>
    </collision>
    <inertial>
      <origin rpy="0 0 0" xyz="-0.021 0 0.01625"/>			
      <mass value="0.0005"/>
	  <default_inertia />
    </inertial>            
  </link>
  
  <joint name="servo_arti3_P" type="fixed">
    <parent link="muneca_link"/>
    <child link="muneca_link_P"/>  
    <origin xyz="0 0 0" rpy="0 0 0" />
	<axis xyz="1 0 0" />    
  </joint>  

<!--Pinza fija-->
  
  <link name="muneca_link_P">    
	<visual>
      <geometry>
        <box size="0.002 0.04 0.092"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0.03425 0 0.090"/>
      <material name="white">
		<color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0.03425 0 0.090"/>		
	  <geometry>
        <box size="0.002 0.04 0.092"/>
      </geometry>
    </collision>
    <inertial>
      <origin rpy="0 0 0" xyz="0.03425 0 0.090"/>			
      <mass value="0.001"/>
	  <default_inertia />
    </inertial>           
  </link>
  
  <joint name="servo_arti3_PS" type="fixed">
    <parent link="muneca_link"/>
    <child link="muneca_link_PS"/>  
    <origin xyz="0 0 0" rpy="0 0 0" />
	<axis xyz="1 0 0" />    
  </joint>
  
  <link name="muneca_link_PS">    
	<visual>
      <geometry>
        <box size="0.002 0.04 0.037"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0.03225 0 0.0575"/>
      <material name="white">
		<color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0.03225 0 0.0575"/>	
	  <geometry>
        <box size="0.002 0.04 0.037"/>
      </geometry>
    </collision>
    <inertial>
      <origin rpy="0 0 0" xyz="0.03225 0 0.0575"/>			
      <mass value="0.0005"/>
	  <default_inertia />
    </inertial>            
  </link>             
  
  <joint name="pinza" type="revolute">
    <parent link="muneca_link"/>
    <child link="pinza_link"/>
    <origin xyz="-0.00725 0 0.06" rpy="0 0 0" />
    <axis xyz="0 1 0" />
	<default_limit />
	<default_dynamics />     
  </joint>
  
<!--Pinza móvil-->
  
  <link name="pinza_link">    
	<visual>
      <geometry>
        <box size="0.002 0.04 0.092"/>
      </geometry>
      <origin rpy="0 0 0" xyz="-0.027 0 0.030"/>
      <material name="white">
		<color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="-0.027 0 0.030"/>		
	  <geometry>
        <box size="0.002 0.04 0.092"/>
      </geometry>
    </collision>
    <inertial>
      <origin rpy="0 0 0" xyz="-0.027 0 0.030"/>		
      <mass value="0.001"/>
 	  <default_inertia />
    </inertial>           
  </link>  
  
  <joint name="servo_pinza_B" type="fixed">
    <parent link="pinza_link"/>
    <child link="pinza_link_B"/>  
    <origin xyz="0 0 0" rpy="0 0 0" />
	<axis xyz="1 0 0" />    
  </joint>  
  
  <link name="pinza_link_B">    
	<visual>
      <geometry>
        <box size="0.002 0.04 0.032"/>
      </geometry>
      <origin rpy="0 0 0" xyz="-0.025 0 0"/>
      <material name="white">
		<color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="-0.025 0 0"/>		
	  <geometry>
        <box size="0.002 0.04 0.032"/>
      </geometry>
    </collision>
    <inertial>
      <origin rpy="0 0 0" xyz="-0.025 0 0"/>		
      <mass value="0.0005"/>
	  <default_inertia />
    </inertial>           
  </link>
  
  <joint name="servo_pinza_D" type="fixed">
    <parent link="pinza_link"/>
    <child link="pinza_link_SI"/>  
    <origin xyz="0 0 0" rpy="0 0 0" />
	<axis xyz="1 0 0" />    
  </joint>  
  
  <link name="pinza_link_SI">    
	<visual>
      <geometry>
        <box size="0.0375 0.002 0.032"/>
      </geometry>
      <origin rpy="0 0 0" xyz="-0.00725 0.021 0"/>
      <material name="white">
		<color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="-0.00725 0.021 0"/>		
	  <geometry>
        <box size="0.0375 0.002 0.032"/>
      </geometry>
    </collision>
    <inertial>
      <origin rpy="0 0 0" xyz="-0.00725 0.021 0"/>			
      <mass value="0.0005"/>
	  <default_inertia />
    </inertial>        
  </link>
  
  <joint name="servo_pinza_I" type="fixed">
    <parent link="pinza_link"/>
    <child link="pinza_link_SD"/>  
    <origin xyz="0 0 0" rpy="0 0 0" />
	<axis xyz="1 0 0" />    
  </joint>  
  
  <link name="pinza_link_SD">    
	<visual>
      <geometry>
        <box size="0.0375 0.002 0.032"/>
      </geometry>
      <origin rpy="0 0 0" xyz="-0.00725 -0.021 0"/>
      <material name="white">
		<color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="-0.00725 -0.021 0"/>		
	  <geometry>
        <box size="0.0375 0.002 0.032"/>
      </geometry>
    </collision>
    <inertial>
      <origin rpy="0 0 0" xyz="-0.00725 -0.021 0"/>			
      <mass value="0.0005"/>
	  <default_inertia />
    </inertial>            
  </link>

</macro>
     
</robot>

For the macros file, we will create a file named "brazo-macros.xacro" within the folder "src" of our package with the content that is shown below: 

<?xml version="1.0"?>

<robot xmlns:controller="http://playerstage.sourceforge.net/gazebo/xmlschema/#controller">

<macro name="default_inertia">
      <inertia ixx="0.001" ixy="0.0" ixz="0.0" iyy="0.001" iyz="0.0" izz="0.001"/>
</macro>

<macro name="default_inertia_servos">
      <inertia ixx="0.01" ixy="0.0" ixz="0.0" iyy="0.01" iyz="0.0" izz="0.01"/>
</macro>

<macro name="default_limit">
    <limit effort="100.0" lower="-2.62" upper="2.62" velocity="3"/>
</macro>

<macro name="default_dynamics">
      <dynamics fricction="0" damping="0" />
</macro>

<macro name="servo" params="nombre">  
  <link name="${nombre}_link">
    <visual>
      <geometry>
        <box size="0.04 0.032 0.05"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0 0 0.0905"/>
      <material name="black" />
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 0 0.0905"/>		
	  <geometry>
        <box size="0.04 0.032 0.05"/>
      </geometry>
    </collision>
    <inertial>
      <origin rpy="0 0 0" xyz="0 0 0.0905"/>		
      <mass value="0.055"/>
	  <default_inertia_servos />
    </inertial>             
  </link>
</macro>

<macro name="base" params="nombre">    
  <link name="${nombre}_link_B">    
	<visual>
      <geometry>
        <box size="0.04 0.032 0.020"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0 0 0.0555"/>
      <material name="white">
		<color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 0 0.0555"/>		
	  <geometry>
        <box size="0.04 0.032 0.02"/>
      </geometry>
    </collision>
    <inertial>
      <origin rpy="0 0 0" xyz="0 0 0.0555"/>			
      <mass value="0.001"/>
	  <default_inertia />
    </inertial>           
  </link>
</macro> 

<macro name="soporte" params="nombre simetrico lado">    
  <link name="${nombre}_link_S${lado}">    
	<visual>
      <geometry>
        <box size="0.002 0.032 0.067"/>
      </geometry>
      <origin rpy="0 0 0" xyz="${simetrico*0.021} 0 0.022"/>
      <material name="white">
		<color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="${simetrico*0.021} 0 0.022"/>		
	  <geometry>
        <box size="0.002 0.032 0.067"/>
      </geometry>
    </collision>
    <inertial>
      <origin rpy="0 0 0" xyz="${simetrico*0.021} 0 0.022"/>			
      <mass value="0.001"/>
	  <default_inertia />
    </inertial>           
  </link>
</macro>

</robot>

For the placement file, we will create a file named "brazo.urdf.xacro" within the folder "src" of our package with the content that is shown below: 

<?xml version="1.0"?>

<robot name="MYRAbot-arm"
       xmlns:xi="http://www.w3.org/2001/XInclude"
       xmlns:gazebo="http://playerstage.sourceforge.net/gazebo/xmlschema/#gz"
       xmlns:model="http://playerstage.sourceforge.net/gazebo/xmlschema/#model"
       xmlns:sensor="http://playerstage.sourceforge.net/gazebo/xmlschema/#sensor"
       xmlns:body="http://playerstage.sourceforge.net/gazebo/xmlschema/#body"
       xmlns:geom="http://playerstage.sourceforge.net/gazebo/xmlschema/#geom"
       xmlns:joint="http://playerstage.sourceforge.net/gazebo/xmlschema/#joint"
       xmlns:interface="http://playerstage.sourceforge.net/gazebo/xmlschema/#interface"
       xmlns:rendering="http://playerstage.sourceforge.net/gazebo/xmlschema/#rendering"
       xmlns:renderable="http://playerstage.sourceforge.net/gazebo/xmlschema/#renderable"
       xmlns:controller="http://playerstage.sourceforge.net/gazebo/xmlschema/#controller"
       xmlns:physics="http://playerstage.sourceforge.net/gazebo/xmlschema/#physics">
	
	<include filename="$(find brazo_fer_modelo)/urdf/brazo.xacro" />
	
	<link name="world" />
	
	<brazo parent="world">
		<origin rpy="0 0 0" xyz="0 0 0"/>
	</brazo>

</robot>

Model analysis

As we have used xacro in order to simplify and to make the code more editable, we will execute the next commands in a terminal in order to obtain the URDF file processed: 

roscd brazo_fer_modelo
cd urdf
rosrun xacro xacro.py brazo.urdf.xacro > brazo.urdf

We will execute the next command in a terminal to check the model: 

rosrun urdf_parser check_urdf brazo.urdf

We must obtain something similar to the following: 

robot name is: MYRAbot_arm
---------- Successfully Parsed XML ---------------
root Link: world has 1 child(ren)
    child(1):  base_link
        child(1):  hombro_link
            child(1):  brazo_link
                child(1):  antebrazo_link
                    child(1):  muneca_link
                        child(1):  pinza_link
                            child(1):  pinza_link_B
                            child(2):  pinza_link_SI
                            child(3):  pinza_link_SD
                        child(2):  muneca_link_B
                        child(3):  muneca_link_SI
                        child(4):  muneca_link_SD
                        child(5):  muneca_link_P
                        child(6):  muneca_link_PS
                    child(2):  antebrazo_link_B
                    child(3):  antebrazo_link_SI
                    child(4):  antebrazo_link_SD
                child(2):  brazo_link_B
                child(3):  brazo_link_SI
                child(4):  brazo_link_SD

We will execute the next command in a terminal in order to see the graphic tree generated in a .pdf file: 

rosrun urdf_parser urdf_to_graphiz brazo.urdf

We must obtain something similar to the following:

Árbol de relaciones modelo URBF para el brazo del MYRAbot

Visual test of the model

We will create a file named "brazo_rviz.launch" within the folder "launch" of our package with the content that is shown below in order to display the model and to check the joints: 

<launch>

  <param name="robot_description" command="$(find xacro)/xacro.py '$(find brazo_fer_modelo)/urdf/brazo.urdf.xacro'" />

  <node name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher" />

  <param name="use_gui" value="true"/>

  <node name="robot_state_publisher" pkg="robot_state_publisher" type="state_publisher" />

  <node name="rviz" pkg="rviz" type="rviz" />

</launch>

We will execute the next command in a terminal in order to start the launcher: 

roslaunch brazo_fer_modelo brazo_rviz.launch

The launcher starts rviz and the GUI of joint_state_publisher. We have to set in "Global Options" the field "Fixed Frame" to "/world" link. We can change the position of the joints using the sliders of the GUI of joint_state_publisher. We must obtain something similar to the following:

Loaded model in rviz and the GUI of joint_state_publisher

Control of the joints for simulation

We have to add a controller to each mobile joint in order to simulate the servo motors Dynamixel AX-12A in gazebo

Previous steps

We will execute the next commands in a terminal in order to install the control stacks of the PR2 robot (pr2_simulator, pr2_mechanism and [http://wiki.ros.org/pr2_controllers pr2_controllers): 

sudo atp-get update
sudo apt-get install ros-VERSIÓN_ROS-pr2-simulator ros-VERSIÓN_ROS-pr2-mechanism ros-VERSIÓN_ROS-pr2-controllers

To add controllers to mobile joints

Modification of the URDF

We have to set the materials, properties, transmissions and controllers for our URDF model in gazebo.

We will add the next code lines before the tag "</robot>" within the file "brazo-macros.xacro": 

<macro name="gazebo_propiedades_link" params="nombre material">
  <gazebo reference="${nombre}">
	<mu1>0.5</mu1>
	<mu2>0.5</mu2>
	<material>Gazebo/${material}</material>
    <selfCollide>true</selfCollide>
    <turnGravityOff>false</turnGravityOff> 
  </gazebo>
</macro>

<macro name="gazebo_propiedades_joint" params="nombre">
 <gazebo reference="${nombre}">
    <erp>0.1</erp>
    <stopKd value="1000000.0" />
    <stopKp value="10000000.0" />
    <fudgeFactor value="0.5" />
 </gazebo>
</macro> 

<gazebo>   
     <controller:gazebo_ros_controller_manager name="gazebo_ros_controller_manager" plugin="libgazebo_ros_controller_manager.so">
          <alwaysOn>true</alwaysOn>
          <updateRate>1000.0</updateRate>
     </controller:gazebo_ros_controller_manager>
</gazebo>

 <transmission type="pr2_mechanism_model/SimpleTransmission" name="base_trans">
    <actuator name="base_motor" />
    <joint name="base" />
    <mechanicalReduction>1.0</mechanicalReduction>
    <motorTorqueConstant>1.0</motorTorqueConstant>
 </transmission>

 <transmission type="pr2_mechanism_model/SimpleTransmission" name="arti1_trans">
    <actuator name="arti1_motor" />
    <joint name="arti1" />
    <mechanicalReduction>1.0</mechanicalReduction>
    <motorTorqueConstant>1.0</motorTorqueConstant>
 </transmission>              
 
 <transmission type="pr2_mechanism_model/SimpleTransmission" name="arti2_trans">
    <actuator name="arti2_motor" />
    <joint name="arti2" />
    <mechanicalReduction>1.0</mechanicalReduction>
    <motorTorqueConstant>1.0</motorTorqueConstant>
 </transmission>
 
 <transmission type="pr2_mechanism_model/SimpleTransmission" name="arti3_trans">
    <actuator name="arti3_motor" />
    <joint name="arti3" />
    <mechanicalReduction>1.0</mechanicalReduction>
    <motorTorqueConstant>1.0</motorTorqueConstant>
 </transmission>

 <transmission type="pr2_mechanism_model/SimpleTransmission" name="pinza_trans">
    <actuator name="pinza_motor" />
    <joint name="pinza" />
    <mechanicalReduction>1.0</mechanicalReduction>
    <motorTorqueConstant>1.0</motorTorqueConstant>
 </transmission>

We will add the next code lines before the tag "</macro>" within the file "brazo.xacro": 

<gazebo_propiedades_link nombre="base_brazo_link" material="Black" />

<gazebo_propiedades_link nombre="hombro_link" material="Black" />
  
<gazebo_propiedades_link nombre="brazo_link" material="Black" />  
  
<gazebo_propiedades_link nombre="antebrazo_link" material="Black" />
   
<gazebo_propiedades_link nombre="muneca_link" material="Black" />
  
<gazebo_propiedades_link nombre="brazo_link_B" material="White" />   
  
<gazebo_propiedades_link nombre="brazo_link_SI" material="White" /> 

<gazebo_propiedades_link nombre="brazo_link_SD" material="White" />     

<gazebo_propiedades_link nombre="antebrazo_link_B" material="White" />   

<gazebo_propiedades_link nombre="antebrazo_link_SI" material="White" />   

<gazebo_propiedades_link nombre="antebrazo_link_SD" material="White" />   
  
<gazebo_propiedades_link nombre="muneca_link_B" material="White" />   

<gazebo_propiedades_link nombre="muneca_link_SI" material="White" />   
  
<gazebo_propiedades_link nombre="muneca_link_SD" material="White" />   

<gazebo_propiedades_link nombre="muneca_link_P" material="White" /> 

<gazebo_propiedades_link nombre="muneca_link_PS" material="White" />     
  
<gazebo_propiedades_link nombre="pinza_link" material="White" />   
 
<gazebo_propiedades_link nombre="pinza_link_B" material="White" />   
  
<gazebo_propiedades_link nombre="pinza_link_SI" material="White" />   
   
<gazebo_propiedades_link nombre="pinza_link_SD" material="White" /> 

<gazebo_propiedades_joint nombre="base" />
  
<gazebo_propiedades_joint nombre="arti1" />

<gazebo_propiedades_joint nombre="arti2" />

<gazebo_propiedades_joint nombre="arti3" />
 
<gazebo_propiedades_joint nombre="pinza" />

Creation of the configuration file

We have used two controllers for each mobile joint, one for velocity control and one for position control. Each controller is a PID regulator. We will create a file named "controllers.yaml" within our package with the content that is shown below in order to configure the PID regulators of each mobile joint: 

base_pos_controller:
  type: robot_mechanism_controllers/JointPositionController
  joint: base
  pid: &base_pos
    p: 2.0
    i: 0.5
    d: 0.0
    i_clamp: 10.0

arti1_pos_controller:
  type: robot_mechanism_controllers/JointPositionController
  joint: arti1
  pid: &arti1_pos
    p: 2.0
    i: 0.5
    d: 0.0
    i_clamp: 10.0

arti2_pos_controller:
  type: robot_mechanism_controllers/JointPositionController
  joint: arti2
  pid: &arti2_pos
    p: 2.0
    i: 0.5
    d: 0.0
    i_clamp: 10.0

arti3_pos_controller:
  type: robot_mechanism_controllers/JointPositionController
  joint: arti3
  pid: &arti3_pos
    p: 2.0
    i: 0.5
    d: 0.0
    i_clamp: 10.0

pinza_pos_controller:
  type: robot_mechanism_controllers/JointPositionController
  joint: pinza
  pid: &pinza_pos
    p: 2.0
    i: 0.5
    d: 0.0
    i_clamp: 10.0

base_vel_controller:
  type: robot_mechanism_controllers/JointVelocityController
  joint: base
  pid: &base_vel
    p: 2.0
    i: 0.5
    i_clamp: 10.0
    
arti1_vel_controller:
  type: robot_mechanism_controllers/JointVelocityController
  joint: arti1
  pid: &arti1_vel
    p: 2.0
    i: 0.5
    i_clamp: 10.0         

arti2_vel_controller:
  type: robot_mechanism_controllers/JointVelocityController
  joint: arti2
  pid: &arti2_vel
    p: 2.0
    i: 0.5
    i_clamp: 10.0 
    
arti3_vel_controller:
  type: robot_mechanism_controllers/JointVelocityController
  joint: arti3
  pid: &arti3_vel
    p: 2.0
    i: 0.5
    i_clamp: 10.0   
    
pinza_vel_controller:
  type: robot_mechanism_controllers/JointVelocityController
  joint: pinza
  pid: &pinza_vel
    p: 2.0
    i: 0.5
    i_clamp: 10.0

Loading the model in gazebo

We will create a file named "brazo_gazebo.launch" within the folder "launch" of our package with the content that is shown below in order to start gazebo and to load the model and the controllers: 

<launch>

  <include file="$(find gazebo_worlds)/launch/empty_world.launch"/>

  <param name="robot_description" command="$(find xacro)/xacro.py '$(find brazo_fer_modelo)/brazo.urdf.xacro'" />

  <node name="robot_state_publisher" pkg="robot_state_publisher" type="state_publisher" />

  <node name="spawn_brazo" pkg="gazebo" type="spawn_model" args="-urdf -param robot_description -model MYRAbot_arm" respawn="false" output="screen" />
 
  <rosparam file="$(find brazo_fer_modelo)/controllers.yaml" command="load"/>

  <node name="spawn_controller" pkg="pr2_controller_manager" type="spawner" args="base_pos_controller arti1_pos_controller arti2_pos_controller arti3_pos_controller pinza_pos_controller base_vel_controller arti1_vel_controller arti2_vel_controller arti3_vel_controller pinza_vel_controller" respawn="false" output="screen" />
 
</launch>

We will execute the next command in a terminal in order to start the launcher: 

roslaunch brazo_fer_modelo brazo.gazebo.launch

We can see the arm model in vertical position placed in the point xyz=(0 0 0) of a empty world in gazebo.

MYRAbot's arm model in gazebo

We will execute the next command in a new terminal in order to check that the controllers have been loaded properly: 

rostopic echo

We must obtain something similar to the following, where the topic NAME_CONTROLLER/command is the set point and the topic NAME_CONTROLLER/status is the status data: 

/arti1_pos_controller/command
/arti1_pos_controller/state
/arti1_vel_controller/command
/arti1_vel_controller/state
/arti2_pos_controller/command
/arti2_pos_controller/state
/arti2_vel_controller/command
/arti2_vel_controller/state
/arti3_pos_controller/command
/arti3_pos_controller/state
/arti3_vel_controller/command
/arti3_vel_controller/state
/base_pos_controller/command
/base_pos_controller/state
/base_vel_controller/command
/base_vel_controller/state
/clock
/gazebo/link_states
/gazebo/model_states
/gazebo/parameter_descriptions
/gazebo/parameter_updates
/gazebo/paused
/gazebo/set_link_state
/gazebo/set_model_stat
/joint_states
/mechanism_statistics
/pinza_pos_controller/command
/pinza_pos_controller/state
/pinza_vel_controller/command
/pinza_vel_controller/state
/rosout
/rosout_agg
/tf

Interface program (gazebo-control programs)

We have create a program that communicates the arm's control programs with gazebo controllers. We will create a file named "control_modelo.cpp" within the folder "src" of our package with the content that is shown below:

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