Turtlebot Linear Y has no response

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Hi,

I am trying to do Turtlebot Simulation. I am giving Linear x & Linear y . But it seems like linear Y has no effect.

Then i tried below simple code to check linear y effect. after code run there is no movement in Y direction. Please tell reason-

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#!/usr/bin/env python 

import rospy
from geometry_msgs.msg import Twist

def Move():
        Pub = rospy.Publisher('mobile_base/commands/velocity' , Twist , queue_size=20)

        command = Twist()
        command.linear.x = 0
        command.linear.y = 1
        command.linear.z = 0
        command.angular.x = 0
        command.angular.y = 0
        command.angular.z = 0

        r = rospy.Rate(100)

        while not rospy.is_shutdown():
                Pub.publish(command)

                r.sleep()

if __name__ == '__main__' :
        rospy.init_node('TurtleControl')
        Move()

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