Ask Your Question
2

smach subscriber publisher

asked 2011-07-07 00:59:24 -0600

boy gravatar image

hello everyone,

I'm new to the ROS society, and I have some questions.

I've made a simple state machine,publisher and subscriber as was shown in the tutorials, but how can I use date obtained from the subscriber(e.g a simple String) to make a transition between two states in the state machine??

greetings

edit retag flag offensive close merge delete

3 Answers

Sort by » oldest newest most voted
4

answered 2011-07-07 09:55:01 -0600

Wim gravatar image

A smach state is simply a Python class (see the example in this tutorial), so you can add a normal ROS subscriber to that class if you want.

This means, in the subscriber callback you can store the message data (a string in your case) as a class memeber, and in the execute callback you can make decisions about outcomes based on tis class member.

edit flag offensive delete link more

Comments

Thanks for the answer Wim, but I still have some problems with it( Maybe its because I'm a rookie) . Could you(if it is not too much) give a small example??
boy gravatar imageboy ( 2011-07-07 21:48:21 -0600 )edit
4

answered 2011-07-07 22:39:43 -0600

Ugo gravatar image

Hi,

This small (and untested) example subscribes on a topic and return success if 2 is received on this topic in the next 30 seconds.

#!/usr/bin/env python
import roslib; roslib.load_manifest('smach_example')
import rospy
import smach
import smach_ros
from std_msgs.msg import Int16
import time
import threading

class WaitForTwo(smach.State):
    def __init__(self):
        smach.State.__init__(self, outcomes=['success', 'in_progress', 'failed'])

        self.mutex = threading.Lock()
        self.two_received = False

        self.subscriber = rospy.Subscriber('/test', Int16, self.callback)

    def callback(self, data):
        self.mutex.acquire()
        if data.data == 2:
            self.two_received = True
        self.mutex.release()

    def execute(self):
        #wait for a maximum of 30 seconds 
        for i in range(0, 300):
            self.mutex.acquire()
            if self.two_received:
                #ok we received 2
                return 'success'

            self.mutex.release()

            time.sleep(.1)
            #still waiting
            return 'in_progress'
        #we didn't get 2 in the 30 sec
        return 'failed'
edit flag offensive delete link more
1

answered 2013-01-31 02:37:00 -0600

felix k gravatar image

updated 2013-02-01 03:58:54 -0600

Based on the callback-and-loop-in-execute-with-mutex scheme Ugo mentioned in his answer I made a fully generic message receiver smach.State class that helps a lot for receiving messages in a SMACH machine, as I couldn't made use of the the MonitorState.

The current feature set includes waiting, timeout, userdata access and latching, of course optional.

Class WaitForMsgState in module util.py in unreleased package uashh_smach. The class CheckSmachEnabledState right underneath is a simple usage example

As the whole class has a lot of (docstring) lines I just post the up-to-date link to the module's file in the repository (and just for read only reference the commit-static link to its code line).

edit flag offensive delete link more

Comments

1

Felix, I just added this to a new page here to document 3rd party SMACH states: http://ros.org/wiki/executive_smach/AdditionalStateTypes

jbohren gravatar imagejbohren ( 2013-01-31 03:15:08 -0600 )edit

Thanks alot for that cornerstone, that's exactly what I have been missing since I started using SMACH, a way to find existing useful SMACH code. (And what I planned to do after final code and modules cleanup..) I'll add my other states soon!

felix k gravatar imagefelix k ( 2013-01-31 23:35:28 -0600 )edit

Hi, I am doing the same with my Smach machine.

Tony K gravatar imageTony K ( 2013-07-11 14:28:04 -0600 )edit

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Question Tools

3 followers

Stats

Asked: 2011-07-07 00:59:24 -0600

Seen: 4,057 times

Last updated: Feb 01 '13