Cannot get turtle2 to move Ex2.3

I am working with the code provided as an example, no changes at all.

#!/usr/bin/env python
import sys
import rospy
import math
import tf
import geometry_msgs.msg

if __name__ == '__main__':

    listener = tf.TransformListener()

    if len(sys.argv) < 3:
        print("usage: follower_model_name model_to_be_followed_name")
        follower_model_name = sys.argv[1]
        model_to_be_followed_name = sys.argv[2]
        turtle_vel = rospy.Publisher(follower_model_name+'/cmd_vel', geometry_msgs.msg.Twist,queue_size=1)
        rate = rospy.Rate(10.0)
        ctrl_c = False
        follower_model_frame = "/"+follower_model_name
        model_to_be_followed_frame = "/"+model_to_be_followed_name
        def shutdownhook():
            # works better than the rospy.is_shut_down()
            global ctrl_c
            print "shutdown time! Stop the robot"
            cmd = geometry_msgs.msg.Twist()
            cmd.linear.x = 0.0
            cmd.angular.z = 0.0
            ctrl_c = True

        while not ctrl_c:
                (trans,rot) = listener.lookupTransform(follower_model_frame, model_to_be_followed_frame, rospy.Time(0))
            except (tf.LookupException, tf.ConnectivityException, tf.ExtrapolationException):
            angular = 4 * math.atan2(trans[1], trans[0])
            linear = 0.5 * math.sqrt(trans[0] ** 2 + trans[1] ** 2)
            cmd = geometry_msgs.msg.Twist()
            cmd.linear.x = linear
            cmd.angular.z = angular

All the topics needed are being published (turtle 1 and 2/cmd_vel).

I found out that the problem I am having is that my code gets caught in the except part in the loop, so I never get any data to work with. Now, I am not exactly sure why this is happening, or what am I missing.

Thank you in advance.


So the issue must have been that you werent launching the TF publisher. Remember that this code uses the TF published with the previous python script to then calcualte the cmd_vel t move the IRobot to the RealTurtle.

These should be the commands that you should launch and the code to make this work:


Now launch the moving based on the TF published with the previous launch

python turtle2 turtle1

It should move the irobot to the realturtle, I made a minor modification to detect when there is no transform between the two models, but it not necessary for this to work.