timed_out_and_back.py

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#!/usr/bin/env python

""" timed_out_and_back.py - Version 0.1 2012-03-24

    A basic demo of the using odometry data to move the robot along
    and out-and-back trajectory.

    Created for the Pi Robot Project: http://www.pirobot.org
    Copyright (c) 2012 Patrick Goebel.  All rights reserved.

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.5
    
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details at:
    
    http://www.gnu.org/licenses/gpl.html
      
"""

#import roslib; roslib.load_manifest('rbx1_nav')
import rospy
from geometry_msgs.msg import Twist
from math import pi

class OutAndBack():
    def __init__(self):
        # Give the node a name
        rospy.init_node('out_and_back', anonymous=False)

        # Set rospy to exectute a shutdown function when exiting       
        rospy.on_shutdown(self.shutdown)
        
        # Publisher to control the robot's speed
        self.cmd_vel = rospy.Publisher('/cmd_vel', Twist)
        
        # How fast will we update the robot's movement?
        rate = 50
        
        # Set the equivalent ROS rate variable
        r = rospy.Rate(rate)
        
        # Set the forward linear speed to 0.2 meters per second 
        linear_speed = 0.2
        
        # Set the travel distance to 1.0 meters
        goal_distance = 1.0
        
        # How long should it take us to get there?
        linear_duration = goal_distance / linear_speed
        
        # Set the rotation speed to 1.0 radians per second
        angular_speed = 1.0
        
        # Set the rotation angle to Pi radians (180 degrees)
        goal_angle = pi
        
        # How long should it take to rotate?
        angular_duration = goal_angle / angular_speed
     
        # Loop through the two legs of the trip  
        for i in range(2):
            # Initialize the movement command
            move_cmd = Twist()
            
            # Set the forward speed
            move_cmd.linear.x = linear_speed
            
            # Move forward for a time to go the desired distance
            ticks = int(linear_duration * rate)
            
            for t in range(ticks):
                self.cmd_vel.publish(move_cmd)
                r.sleep()
            
            # Stop the robot before the rotation
            move_cmd = Twist()
            self.cmd_vel.publish(move_cmd)
            rospy.sleep(1)
            
            # Now rotate left roughly 180 degrees  
            
            # Set the angular speed
            move_cmd.angular.z = angular_speed

            # Rotate for a time to go 180 degrees
            ticks = int(goal_angle * rate)
            
            for t in range(ticks):           
                self.cmd_vel.publish(move_cmd)
                r.sleep()
                
            # Stop the robot before the next leg
            move_cmd = Twist()
            self.cmd_vel.publish(move_cmd)
            rospy.sleep(1)    
            
        # Stop the robot
        self.cmd_vel.publish(Twist())
        
    def shutdown(self):
        # Always stop the robot when shutting down the node.
        rospy.loginfo("Stopping the robot...")
        self.cmd_vel.publish(Twist())
        rospy.sleep(1)
 
if __name__ == '__main__':
    try:
        OutAndBack()
    except:
        rospy.loginfo("Out-and-Back node terminated.")