chandyalex/pegasus_gazebo_plugins

gazebo_plugin to solve the issue that URDF not support Closed loop chains.

pegasus_gazebo_plugins

Overview

This is pegasus_gazebo_plugins package developed for our quadruped robot "Pegasus",which is used for Pegasus robots in gazebo simulation and ROS environment.closed_loop_plugin is one of the plugins that open here,to solve the issue that URDF not support Closed loop chains.

*Author: Angel_jj
*Department ：The Chinese University of Hong Kong,Shenzhen，IRIM(Institute of Robotics and Intelligent Manufacturing)
*Maintainer: Angel_jj, [email protected]

Introduction

Citing

Tutorial: Using a URDF in Gazebohttp://gazebosim.org/tutorials?tut=ros_urdf&cat=connect_ros

The Universal Robotic Description Format (URDF) is an XML file format used in ROS to describe all elements of a robot. To use a URDF file in Gazebo, some additional simulation-specific tags must be added to work properly with Gazebo. This tutorial explains the necessary steps to successfully use your URDF-based robot in Gazebo, saving you from having to create a separate SDF file from scratch and duplicating description formats. Under the hood, Gazebo will then convert the URDF to SDF automatically.

Background
While URDFs are a useful and standardized format in ROS, they are lacking many features and have not been updated to deal with the evolving needs of robotics. URDF can only specify the kinematic and dynamic properties of a single robot in isolation. URDF can not specify the pose of the robot itself within a world. It is also not a universal description format since it cannot specify joint loops (parallel linkages), and it lacks friction and other properties. Additionally, it cannot specify things that are not robots, such as lights, heightmaps, etc.

On the implementation side, the URDF syntax breaks proper formatting with heavy use of XML attributes, which in turn makes URDF more inflexible. There is also no mechanism for backward compatibility.

To deal with this issue, a new format called the Simulation Description Format (SDF) was created for use in Gazebo to solve the shortcomings of URDF. SDF is a complete description for everything from the world level down to the robot level. It is scalable, and makes it easy to add and modify elements. The SDF format is itself described using XML, which facilitates a simple upgrade tool to migrate old versions to new versions. It is also self-descriptive.
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Summary

The URDF served the ROS, it has several notable shortcomings.one is it does not support closed loop chains.
The SDF served the gazebo, support closed loop chains - this can be achieved by allowing two different joints to have the same child link but different parents
The closed_loop_plugin works after the robot model is converted from urdf to sdf, inserting a new joint into the SDF.

Building

In order to install the pegasus_gazebo_plugins, clone the latest version from this repository into your catkin workspace and compile the package using ROS.

cd catkin_workspace/src
git clone https://github.com/wojiaojiao/pegasus_gazebo_plugins.git
cd ../
catkin_make

Usage

This closed_loop_plugin just like a button that connects two links,
<joint> the name of the added joint
<child> the name that child coordinate of the added joint
<parent> the name that parent coordinate of the added joint
<position> the position where two links are connected,x,y,z．
<rotation> the rotation where two links are connected,roll,pitch,yaw．

add to your robot.urdf：

     <gazebo>
       <plugin name="Myrobot_ClosedLoopPlugin" filename="libpegasus_gazebo_closed_loop_plugin.so">
           <joint>add_joint</joint>
           <child>add_joint_child_link</child>
           <parent>add_joint_parent_link</parent>
           <position>0.0 0.0 0.0</position>
           <rotation>0.00 -0.00 0.00</rotation>
       </plugin>
     </gazebo>

exmaple

The following is a four-link closed-loop chain

     <gazebo>
       <plugin name="Myrobot_ClosedLoopPlugin" filename="libpegasus_gazebo_closed_loop_plugin.so">
           <joint>red_green_joint</joint>
           <child>red_link</child>
           <parent>green_link</parent>
           <position>0.0 0.0 0.0</position>
           <rotation>0.00 -0.00 0.00</rotation>
       </plugin>
     </gazebo>

Here is the plugin version for gazebo 9.0.0

pegasus_gazebo_plugins_Gv9_v2.zip

Related reference：https://github.com/wojiaojiao/pegasus_gazebo_plugins/issues/3

Bugs & Feature Requests

Please report bugs and request features using the Issue Tracker.