实操 | Simulating a Fetch robot in Gazebo

Installation

Before installing the simulation environment, make sure your desktop is setup with a standard installation of ROS Indigo on Ubuntu 14.04. Once your APT repositories are configured, you can install the simulator:

$ sudo apt-get update
$ sudo apt-get install ros-indigo-fetch-gazebo-demo

Warning

Never run the simulator on the robot. Simulation requires that the ROS parameter use_sim_time be set to true, which will cause the robot drivers to stop working correctly. In addition, be sure to never start the simulator in a terminal that has the ROS_MASTER_URI set to your robot for the same reasons.

Starting the Simulator

The fetch_gazebo and fetch_gazebo_demo packages provide the Gazebo environment for Fetch. fetch_gazebo includes several launch files:

• simulation.launch spawns a robot in an empty world.
• playground.launch spawns a robot inside a lab-like test environment. This environment has some tables with items that may be picked up and manipulated. It also has a pre-made map which can be used to test out robot navigation and some simple demonstrations of object grasping.

To start the simplest environment:

$ roslaunch fetch_gazebo simulation.launch

Note that all of the environments will prepare the robot by tucking the arm and giving the head an initial command.

Note: Possibly you don't see the lidar scan as in the above picture. That is because the default set of visibility of lidar scan is false. You can manually modify it in its .xacro file.

$ roscd fetch_gazebo

$ cd robots

$ gedit fetch.gazebo.xacro

locate "laser_link" block:

modify this line:

<visualize>false</visualize>

as

<visualize>true</visualize>

Visualizing with RVIZ

Even though Gazebo has a graphical visualization, RVIZ is still the preferred tool for interacting with your robot.

$ rosrun rviz rviz

You can now manually set up your RVIZ visualization or re-run RVIZ with a configuration file using the command line. The default .rviz configuration file for Fetch can be loaded using:

$ roscd fetch_navigation/config
$ rviz -d navigation.rviz

 To start with playground.launch:

$ roslaunch fetch_gazebo playground.launch

Check it in rviz:

Running the Mobile Manipulation Demo

There is a fully integrated demo showing navigation, perception and MoveIt! working together on the robot in simulation. To run the demo, start Gazebo simulator with the playground:

>$ roslaunch fetch_gazebo playground.launch

Wait until the simulator is fully running and then run the demo launch file:

>$ roslaunch fetch_gazebo_demo demo.launch

This will start:

• fetch_nav.launch - this is the navigation stack with a pre-built map of the environment.
• move_group.launch - this is the MoveIt configuration which can plan for the movement of the arm.
• basic_grasping_perception - this is a simple demo found in the simple_grasping package which segments objects on tables and computes grasps for them.
• demo.py - this our specific demo which navigates the robot from the starting pose in Gazebo to the table, raises the torso, lowers the head to look at the table, and then runs perception to generate a goal for MoveIt. The arm will then grasp the cube on the table, tuck the arm and lower the torso. Once the robot is back in this tucked configuration, the navigation stack will be once again called to navigate into the room with the countertop where the robot will place the cube on the other table.

Reference:

Fetch Robotics: Tutorial: Gazebo Simulation