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Print a msg from a Turtlebot3 subscriber

asked 2019-08-20 14:41:13 -0500

Tima1995 gravatar image

updated 2019-08-20 14:44:29 -0500


I am just trying to print a msg that is subscribed from the cmd_vel_rc100 message. Here is some of the code:

def moving(self):
        self.pub_cmd_vel = rospy.Publisher('cmd_vel', Twist, queue_size=5)
        while self.finish:
            vel_cmd = Twist()
            vel_cmd_received = Twist()
            vel_cmd.linear.x = 0
            vel_cmd_received = rospy.Subscriber('cmd_vel_rc100', Twist, queue_size=5)
            print vel_cmd_received
            self.finish = False

When I run the node, I see the following in the terminal for the cmd_vel_rc100:

<rospy.topics.Subscriber object at 0x7fd7a0436d50>

Normally, the node must be of type Twist(). My question is now, why don´t I see the normal Twist message?

Thanks for your help!

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answered 2019-08-20 17:24:29 -0500

You need to use a different method to receive just a single message without a callback as you're trying to in your code. The rospy.wait_for_message() will do what you expect, blocking execution until a message is received and returning that message.

A rospy.Subscriber object is used when you want to register a callback function to receive messages whenever the arrive on a topic. You normally create it once when your node is created and destroy it when it closes. This is described in the tutorial here.

Hope this helps.

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Worked well, thanks :)

Tima1995 gravatar image Tima1995  ( 2019-08-21 01:10:34 -0500 )edit

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Asked: 2019-08-20 14:41:13 -0500

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Last updated: Aug 20 '19