Overview

Prerequisites:

Make a Mobile Robot

Make a Simple Gripper

This tutorial explains how to create a composite robot from existing robot parts, i.e. mobile base, simple arm and simple gripper.

Robot Components

Start up gazebo and make sure you can load the models from the two previous tutorials.

Mobile Base

1. Per instructions in Make a Mobile Robot tutorial, you should have a mobile base robot at your disposal:

   

2. For this exercise, modify ~/.gazebo/models/my_robot/model.sdf to make the model larger so it can accommodate the gripper we are about to append to it:

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

   update the contents to make the model body larger and re-position the wheels accordingly:

   <?xml version='1.0'?>
   <sdf version='1.5'>
     <model name="mobile_base">
       <link name='chassis'>
         <pose>0 0 .25 0 0 0</pose>
   
         <inertial>
           <mass>20.0</mass>
           <pose>-0.1 0 -0.1 0 0 0</pose>
           <inertia>
             <ixx>0.5</ixx>
             <iyy>1.0</iyy>
             <izz>0.1</izz>
           </inertia>
         </inertial>
   
         <collision name='collision'>
           <geometry>
             <box>
               <size>2 1 0.3</size>
             </box>
           </geometry>
         </collision>
   
         <visual name='visual'>
           <geometry>
             <box>
               <size>2 1 0.3</size>
             </box>
           </geometry>
         </visual>
   
         <collision name='caster_collision'>
           <pose>-0.8 0 -0.125 0 0 0</pose>
           <geometry>
             <sphere>
               <radius>.125</radius>
             </sphere>
           </geometry>
   
           <surface>
             <friction>
               <ode>
                 <mu>0</mu>
                 <mu2>0</mu2>
               </ode>
             </friction>
           </surface>
         </collision>
   
         <visual name='caster_visual'>
           <pose>-0.8 0 -0.125 0 0 0</pose>
           <geometry>
             <sphere>
               <radius>.125</radius>
             </sphere>
           </geometry>
         </visual>
       </link>
       <link name="left_wheel">
         <pose>0.8 0.6 0.125 0 1.5707 1.5707</pose>
         <collision name="collision">
           <geometry>
             <cylinder>
               <radius>.125</radius>
               <length>.05</length>
             </cylinder>
           </geometry>
         </collision>
         <visual name="visual">
           <geometry>
             <cylinder>
               <radius>.125</radius>
               <length>.05</length>
             </cylinder>
           </geometry>
         </visual>
       </link>
   
       <link name="right_wheel">
         <pose>0.8 -0.6 0.125 0 1.5707 1.5707</pose>
         <collision name="collision">
           <geometry>
             <cylinder>
               <radius>.125</radius>
               <length>.05</length>
             </cylinder>
           </geometry>
         </collision>
         <visual name="visual">
           <geometry>
             <cylinder>
               <radius>.125</radius>
               <length>.05</length>
             </cylinder>
           </geometry>
         </visual>
       </link>
   
       <joint type="revolute" name="left_wheel_hinge">
         <pose>0 0 -0.03 0 0 0</pose>
         <child>left_wheel</child>
         <parent>chassis</parent>
         <axis>
           <use_parent_model_frame>true</use_parent_model_frame>
           <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>
           <use_parent_model_frame>true</use_parent_model_frame>
           <xyz>0 1 0</xyz>
         </axis>
       </joint>
   
     </model>
    </sdf>
   

   

Assembling a Composite Robot

1. To create a mobile robot with a simple gripper attached, create a new models directory

   mkdir ~/.gazebo/models/simple_mobile_manipulator
   

   And edit the model config file:

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

   populate it with the following contents:

   <?xml version="1.0"?>
   <model>
     <name>Simple Mobile Manipulator</name>
     <version>1.0</version>
     <sdf version='1.5'>manipulator.sdf</sdf>
   
     <author>
       <name>My Name</name>
       <email>me@my.email</email>
     </author>
   
     <description>
       My simple mobile manipulator
     </description>
   </model>
   

2. Next, create the model SDF file:

   gedit ~/.gazebo/models/simple_mobile_manipulator/manipulator.sdf
   

   and populate with following contents:

   <?xml version="1.0" ?>
   <sdf version="1.5">
     <model name="simple_mobile_manipulator">
   
       <include>
         <uri>model://my_gripper</uri>
         <pose>1.3 0 0.1 0 0 0</pose>
       </include>
   
       <include>
         <uri>model://my_robot</uri>
         <pose>0 0 0 0 0 0</pose>
       </include>
   
       <joint name="arm_gripper_joint" type="fixed">
         <parent>mobile_base::chassis</parent>
         <child>simple_gripper::riser</child>
       </joint>
   
       <!-- attach sensor to the gripper -->
       <include>
         <uri>model://hokuyo</uri>
         <pose>1.3 0 0.3 0 0 0</pose>
       </include>
   
       <joint name="hokuyo_joint" type="fixed">
         <child>hokuyo::link</child>
         <parent>simple_gripper::palm</parent>
       </joint>
   
     </model>
   </sdf>
   

3. Make sure the model.config and manipulator.sdf files above are saved, start Gazebo and spawn the model above by using the insert tab and choosing Simple Mobile Manipulator model. You should see something similar to: