Unit_4 Exercise_4_3 launch file doubt

Course Support ROS Basics In 5 Days (Python)
1

Respected Prof,
I ran the following code before making .launch file

#! /usr/bin/env python

import rospy
from my_custom_srv_msg_pkg.srv import MyCustomServiceMessage, MyCustomServiceMessageResponse # you import the service message python classes generated from my_custom_srv_msg_pkg.srv.
from geometry_msgs.msg import Twist

def my_callback(request):
    rospy.loginfo("The Service move_bb8_in_circle_custom has been called")
    move_circle.linear.x = 0.2
    move_circle.angular.z = 0.2
    
    i = 0
    while i <= request.duration:
        my_pub.publish(move_circle)
        rate.sleep()
        i=i+1
    
    move_circle.linear.x = 0
    move_circle.angular.z = 0
    my_pub.publish(move_circle)

    my_response = MyCustomServiceMessageResponse()
    my_response.success = True
    rospy.loginfo("Finished service move_bb8_in_circle_custom")
    return my_response # the service Response class, in this case MyCustomServiceMessageResponse

rospy.init_node('service_move_bb8_in_circle_custom_server') 
my_service = rospy.Service('/move_bb8_in_circle_custom', MyCustomServiceMessage , my_callback) # create the Service called move_bb8_in_circle_custom with the defined callback
my_pub = rospy.Publisher('/cmd_vel', Twist, queue_size=1)
move_circle = Twist()
rate = rospy.Rate(1)
rospy.loginfo("Service /move_bb8_in_circle_custom Ready")
rospy.spin() # mantain the service open.

Result: The robot moved for the given time, but it didn’t stop after that.
But…When I created .launch file and ran the code again, the robot stopped after the specified amount of time. Would you please tell me why so ?

2

When you ran it as a script, the publisher latches on to the my_pub = rospy.Publisher(’/cmd_vel’, Twist, queue_size=1), so you would need to update the cmd_vel message so it stops. Once you ran it as a launch file, the service can look at the request.duration to make sure that the movement stays within the specified parameter.

3

The request.duration is taken from .srv file. So does that mean that, the pythonfile.py without having launchfile.launch will not take the service_message.srv file into consideration ?

4

It should. I’ll check with your code to see what the issue is

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