My node won't stop publishing

Question

I am following the ROS in 5 days course. I am running a basic node which is publishing movement to the turtlebot. The bot behaves as I expect, however when I kill the instance that is publishing the node (ctrl+C), the robot keeps on spinning. I have no idea why nor how to kill the process... Here is my code:

#! /usr/bin/env python

import rospy
import signal
from std_msgs.msg import Int32 
from geometry_msgs.msg import Twist
from nav_msgs.msg import Odometry
from sensor_msgs.msg import LaserScan

rospy.init_node('guide_robot')
sub = rospy.Subscriber('/kobuki/laser/scan', LaserScan)

# rospy.spin()
rate = rospy.Rate(2)
rate.sleep()
count = Int32()
count.data = 0
pub = rospy.Publisher('/cmd_vel', Twist, queue_size=1)

var = Twist()
while not rospy.is_shutdown(): 
  var.angular.z = 1
  var.linear.x = 0
  pub.publish(var)
  count.data += 1

The only way I've found to stop the robot is by running the code again, but publishing var.angular.z = 0. What am I missing?

Thank you

Answer 1

Hello,

Actually the problem is that the robot uses the last message you sent in the /cmd_vel topic. Even if you stop the node, the last message was a non-zero value, that's the reason it keeps moving.

I suggest two possibilities:

1: ROS node on_shutdown callback You can use the rospy.on_shutdown event callback to send a twist message equals to zero. Take a look at this reference: http://wiki.ros.org/rospy/Overview/Initialization%20and%20Shutdown

The code would be like that:

def myhook():
  print "shutdown time!"
  msg = Twist()
  publisher.publish(msg)

rospy.on_shutdown(myhook)

But ROS does not guarantee the messages are going to be publish (Yes, it is written in their documentation)

Python sigint detector

You can use python sigint detector. It would be something like: There is a topic discussing about this (https://stackoverflow.com/questions/1112343/how-do-i-capture-sigint-in-python)

#!/usr/bin/env python
import signal
import sys
def signal_handler(signal, frame):
        print('You pressed Ctrl+C!')
        sys.exit(0)
signal.signal(signal.SIGINT, signal_handler)
print('Press Ctrl+C')
signal.pause()

My node won't stop publishing

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