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resetting turtlesim programmatically in python

asked 2021-02-23 08:11:51 -0500

shiraz_baig gravatar image

I am writing a python code to control the turtlesim (turtlesim_node). I am using ubuntu 18.04 and ROS melodic. I am successfully moving the turtle as per my commands. But after some commands, I wish to reset the turtle. I have tried various options, but cannot find the right one.
Option 1:
from std_srvs.srv import Empty

rospy.wait_for_service('reset')
clear_bg = rospy.ServiceProxy('reset', Empty)
time.sleep(1)

Option 2:
Used this line instead:
clear_bg = rospy.ServiceProxy('/reset', Empty)

Option 3:
Used this line instead:
clear_bg = rospy.ServiceProxy('turtle1/reset', Empty)

The only option that works is:
import os
os.system('rosservice call /reset')

But Ido not like using system call. Is there any better way of resetting the turtle.

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Comments

Can you try to call your created Object:

resp1 = clear_bg()

Have a look again at the ROS Tutorials here.

turtleMaster20 gravatar image turtleMaster20  ( 2021-02-24 08:37:01 -0500 )edit

I did not create the object. The object is turtle1, created by command "rosrun turtlesim turtlesim_node" This is what I did after your suggestion.

def back_gr():
  rospy.wait_for_service('reset')
  resp1 = rospy.ServiceProxy('reset', Empty)

back_gr()

But neither it gives any error nor it resets the turtle.

shiraz_baig gravatar image shiraz_baig  ( 2021-02-24 23:17:09 -0500 )edit

Add resp1() at the end of def back_gr(). You are creating the Service Object but are yet to call it.

turtleMaster20 gravatar image turtleMaster20  ( 2021-02-25 00:51:40 -0500 )edit

---- here is my full and simplified code, plz tell me what I am doing wrong ---

pub = rospy.Publisher('/turtle1/cmd_vel', Twist, queue_size = 1)
rospy.init_node('turtle_controller', anonymous=True)
twist = Twist()

def back_gr():
   rospy.wait_for_service('reset')
   clear_bg = rospy.ServiceProxy('turtle1/reset', Empty)
   time.sleep(1)

while(True):
   atext = raw_input("next mesg: ")
   if atext[0]=='q': exit()
   if atext[0]=='c': #clear and reset system
      resp1 = back_gr()
      continue

   twist.linear.x = 1; twist.linear.y = 0; twist.linear.z = 0
   twist.angular.x = 0; twist.angular.y = 0; twist.angular.z = 0
   pub.publish(twist)

shiraz_baig gravatar image shiraz_baig  ( 2021-02-25 22:38:04 -0500 )edit

You have created a 'Service' but have not called it.

Between clear_bg = ... and time.sleep(1) add the code clear_bg() so the function back_gr() looks like this:

def back_gr():
 rospy.wait_for_service(`reset`)
 clear_bg = rospy.ServiceProxy('turtle1/reset', Empty)
 clear_bg()
 time.sleep(1)
turtleMaster20 gravatar image turtleMaster20  ( 2021-02-26 00:58:05 -0500 )edit

Thankyou very much. Very good suggestion. It worked very well.

First it did not work. And gave me the error that 'service [/turtle1/reset] unavailable'. I changed the service name from 'turtle1/reset' to 'reset'. Then it worked. I realised that 'reset' is a universal service and resets all turtles instead of just one turtle.

I also learnt, that in this statement clear_bg is not merely a variable. Instead it is a function call (service call) and has to be called to work. Thanks once again.

shiraz_baig gravatar image shiraz_baig  ( 2021-03-01 05:04:43 -0500 )edit

2 Answers

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answered 2021-03-02 00:44:13 -0500

Call the created service by adding clear_bg()

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answered 2021-03-01 05:12:29 -0500

shiraz_baig gravatar image

I was able to solve the problem as guided by turtlemaster20 in the comments. I wish to thank him. This is how it has to be done.
  clear_bg = rospy.ServiceProxy('reset', Empty)
  clear_bg()

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Asked: 2021-02-23 08:11:51 -0500

Seen: 245 times

Last updated: Mar 02