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Python ros multiple publisher

asked 2017-06-06 08:54:40 -0500

Hdifsttar gravatar image

updated 2017-06-06 08:55:46 -0500

Hello,

I'm working on two pioneer 3dx, and i'm trying to make one follow the other. To do that I must first publish a cmd_vel/Twist to my master robot and then publish another cmd_vel/Twist to my slave (based on the space between the robots). The scripts work fine on their own but how can I publish to my master while publishing to my slave since both are using a transform on "twist.linear.x" ?

I wrote this script for the slave :

#!/usr/bin/env python
import getch
import roslib; roslib.load_manifest('p3dx_mover')
import sys
import rospy
import math


from geometry_msgs.msg import Twist
from sensor_msgs.msg import Range

#########Publisher

pub = rospy.Publisher('/r1/cmd_vel', Twist)
rospy.init_node('p3dx_mover')
twist = Twist()

########Variables
rate = rospy.Rate(rospy.get_param('~hz', 10))

s_min = 0.3                         #minimum space between slave & master
s_max = 2                           #maximum space between slave & master
v_max = 0.4                         #maximum velocity of slave
alpha = v_max / (s_max - s_min)     #slope of the velocity function
b = alpha*s_max - v_max             #intercept of the velocity function

#########Subscriber

def callback(msg):
    rospy.loginfo("Sonar 4 detects something at %s m" % round(msg.range,3))
    if msg.range < 0.22:
        rospy.loginfo("Obstacle too close ! Not normal, vehicule stopped (You might want to revise the code)")
        twist.linear.x = 0
        pub.publish(twist)
        rospy.signal_shutdown("Simulation end")

    beta = alpha*msg.range - b
    gamma = min(beta,v_max)
    twist.linear.x = max(0, gamma)

sub = rospy.Subscriber("/r1/sonar4/scan", Range, callback)

#########Loop

while not rospy.is_shutdown() :

    rospy.loginfo("Velocity is "+ str(round(twist.linear.x,3))+ " m/s" )
    pub.publish(twist)
    rate.sleep()

And for the master a simple one such as :

#!/usr/bin/env python
import getch
import roslib; roslib.load_manifest('p3dx_mover')
import sys
import rospy
import math


from geometry_msgs.msg import Twist
from sensor_msgs.msg import Range



#########Publisher

pub = rospy.Publisher('/r2/cmd_vel', Twist)
rospy.init_node('p3dx_mover')
twist = Twist()

########Variables

twist.linear.x = 0
i=0
rate = rospy.Rate(rospy.get_param('~hz', 10))

#########Loop

while not rospy.is_shutdown() :

    twist.linear.x = (math.cos(i) +2)/8
    i+=0.1
    rospy.loginfo("Velocity is "+ str(round(twist.linear.x,3))+ " m/s" )
    pub.publish(twist)
    rate.sleep()

While looking at multiple ros python code, I saw that many use classes and functions to do these sort of things. I tried but since i'm not at ease with these things, nothing worked.

If anyone could help me, feel free to contribute ! If more informations are needed, I remain at your disposal.

Hdifsttar

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Comments

You are on the right track, simply merge both scripts. One publishes to "'/r1/cmd_vel'" the other to '/r2/cmd_vel',

Humpelstilzchen gravatar imageHumpelstilzchen ( 2017-06-06 11:15:54 -0500 )edit

To merge them, simply rename pub to maybe pub1 and pub2 and the twist messages to twist1 and twist2 (or pub_master, pub_slave etc). You will only need one init_node call, so the one node will then be publishing two different twist messages to two different topics.

ufr3c_tjc gravatar imageufr3c_tjc ( 2017-06-06 18:00:33 -0500 )edit

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answered 2017-06-07 03:06:00 -0500

Hdifsttar gravatar image

Thanks @Humpelstilzchen and @ufr3c_tjc. It worked just fine. If anyone's interested here's the code :

#!/usr/bin/env python
import getch
import roslib; roslib.load_manifest('p3dx_mover')
import sys
import rospy
import math


from geometry_msgs.msg import Twist
from sensor_msgs.msg import Range

#########Publisher

pub_r1 = rospy.Publisher('/r1/cmd_vel', Twist)
pub_r2 = rospy.Publisher('/r2/cmd_vel', Twist)
rospy.init_node('p3dx_mover')
twist_r1 = Twist()
twist_r2 = Twist()

########Variables
i=0
rate = rospy.Rate(rospy.get_param('~hz', 10))

s_min = 0.3                         #minimum space between slave & master
s_max = 2                           #maximum space between slave & master
v_max = 0.4                         #maximum velocity of slave
alpha = v_max / (s_max - s_min)     #slope of the velocity function
b = alpha*s_max - v_max             #intercept of the velocity function

#########Subscriber

def callback(msg):
    rospy.loginfo("Sonar 4 detects something at %s m" % round(msg.range,3))
    if msg.range < 0.22:
        rospy.loginfo("Obstacle too close ! Not normal, vehicule stopped (You might want to revise the code)")
        twistr_r1.linear.x = 0
        pub_r1.publish(twist)
        rospy.signal_shutdown("Simulation end")

    beta = alpha*msg.range - b
    gamma = min(beta,v_max)
    twist_r1.linear.x = max(0, gamma)

sub = rospy.Subscriber("/r1/sonar4/scan", Range, callback)

#########Loop

while not rospy.is_shutdown() :

    twist_r2.linear.x = (math.cos(i) +2)/8
    i+=0.1
    rospy.loginfo("r1 velocity is "+ str(round(twist_r1.linear.x,3))+ " m/s" )
    rospy.loginfo("r2 velocity is "+ str(round(twist_r2.linear.x,3))+ " m/s" )
    pub_r1.publish(twist_r1)
    pub_r2.publish(twist_r2)
    rate.sleep()

It might not be the best one, but it works for me.

Hdifsttar

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Asked: 2017-06-06 08:54:40 -0500

Seen: 1,682 times

Last updated: Jun 07 '17