ROS Turtlebot Control

Demo: Result of running these two commands:

rosservice call /turtle/move_to_pose -- -1 -1 -1.57 # (x, y, theta)
rosservice call /turtle/move_to_relative_point -- -1 1 # (x, y)
# Coordinate: +x is front, +y is left; +theta is x to y.

Contents:

• Introduction
• Example of usage
  • Installation
  • Check configuration
  • Start services' server
  • Call services from command line
  • Call services from python functions

Introduction

Main services:

# Control robot to pose.
#   The control algorithm will run in a new thread, 
#   and the service call is immediately finished.
#   If a new command is sent, the old one stops immediatly.
MoveToPose.srv   
MoveToRelativePose.srv   
MoveToPoint.srv  
MoveToRelativePoint.srv

# Get/Set state.
GetPose.srv
StopMoving.srv
IsMoving.srv
ResetPose.srv
SetPose.srv # Only for simulation.

Algorithm: The Move to Pose algorithm is adopted, which uses PID control to reduce the distance between robot pose (x, y, theta) and target pose (x*, y*, theta*). The code is implemented in turtle_lib.py and def _control_robot_to_pose.

Reference: For more details about the algorithm, please see Professor Peter Corke's book Robotics, Vision and Control, Chapter 4.1.1.4--Moving to a Pose.

Main files:

• turtle_lib.py
• turtlebot_server.py
• turtlebot_client.py
• config.yaml

System diagram:

Example of usage

Installation

Download my project:

cd ~/catkin_ws/src # Your catkin workspace
git clone https://github.com/felixchenfy/ros_turtlebot_control

Install Gazebo and Turtlebot related packages. See this: doc/dependencies.md. Make sure the simulated Turtlebot can run in Gazebo.

Check configuration

Open config.yaml, check the section ROS topics/services name used by this package. Make sure the ROS topic/service/tf names are same as yours.

Especially these keywords:

• model_name: It should be one of the turtlebot3_waffle_pi, turtlebot3_waffle, turtlebot3_burger.
• base_frame: You can use $ rosrun tf view_frames to see the tf tree and know your base_frame name.

Start services' server

Launch your real Turtlebot3. Or start a simulation like this:

roscore
roslaunch turtlebot3_gazebo turtlebot3_empty_world.launch 

Start this turtlebot control server:

rosrun ros_turtlebot_control turtlebot_server.py   

Call services from command line

• Move to (x=-1, y=-1, theta=1.57):

rosservice call /turtle/move_to_pose -- -1 -1 1.57

(Notes: -- is a ROS default argument. It's used when the arguments have negative value.)

• Move to (x=1, y=1):

rosservice call /turtle/move_to_point 1 1

• Move to relative (x=1, y=0, theta=1.57):

rosservice call /turtle/move_to_relative_pose 1 0 1.57

• Move to relative (x=0, y=-1):

rosservice call /turtle/move_to_relative_point -- 0 -1

• Reset:

rosservice call /turtle/reset_pose

Call services from python functions

I wrote a class and some unittests in turtlebot_client.py:

class TurtleClient(object):
    def move_to_point(self, x, y):
    def wait_until_stop(self):
    def is_at(self, x, y, theta=None,
    ...

if __name__ == "__main__":
    rospy.init_node("turtlebot_client")
    test_set_pose_IN_SIMULATION_ONLY()  # Not for real robot.
    test_get_and_reset_pose()
    test_move_to_poses()
    test_move_to_points()
    test_change_target_and_stop()

Run it to test the ROS services:

$ rosrun ros_turtlebot_control turtlebot_client.py

You may also copy the file to your own project repo, and then import class TurtleClient to use the python API functions.