return turtlebot to initial position

asked 2016-04-11 18:22:16 -0600

toddwf
16 ●4 ●6 ●8

I have a turtlebot that is executing a simple movement. I'm using the odom message store the initial position. I'm trying to return to the initial position. I'm using some code I found online for navigation to move to a goal, with the goal being the initial odom position. This does not work. The code below ends in the goal failed mode (cancel_goal()). Any ideas?

Do I need tf? or am I just misunderstanding pose? I'm just getting the position from /odom. I don't know if /robot_pose_ekf is better (I would need to install and configure that.), but it's a simple motion--mostly rotation and small movement.

Code snippet:

    #'initial' is the odometry initial position
    goal = MoveBaseGoal()
    goal.target_pose.header.frame_id = 'map'
    goal.target_pose.header.stamp = rospy.Time.now()
    goal.target_pose.pose = Pose(Point(self.initial.position.x, self.initial.position.y, self.initial.position.z),
                             Quaternion(self.initial.orientation.x,self.initial.orientation.y,
                                self.initial.orientation.z, self.initial.orientation.w))

    # Start moving
    self.move_base.send_goal(goal)
    rospy.loginfo('after goal sent')

    # Allow TurtleBot up to 60 seconds to complete task
    success = self.move_base.wait_for_result(rospy.Duration(60))

    state = self.move_base.get_state()
    result = False

    if success and state == GoalStatus.SUCCEEDED:
        # We made it!
        result = True
    else:
        self.move_base.cancel_goal()

answered 2016-04-15 06:16:14 -0600

jorge

2284 ●40 ●71 ●78 https://github.com/corot

First of all, you must think that odom topic doesn't provide you the robot pose, just a dead-reckoning estimation of the robot motion since startup. The robot pose (not the real one, but the one robot "thinks" he is) is obtained by correcting the odom pose with a localization system, as amcl. See the bottom of amcl wiki for a better explanation.

So better you use the initial robot pose as provided by map -> base_footprint tf, e.g:

    try:
        now = rospy.Time.now()
        listener.waitForTransform('map', 'base_footprint', now, rospy.Duration(10.0))
        (bf_trans, bf_rot) = listener.lookupTransform('map', 'base_footprint', now)
    except (tf.LookupException, tf.ConnectivityException, tf.ExtrapolationException) as e:
        rospy.logerr(e)

and send it to move_base instead of the odom first message.

That said, we need more information to guess what is your problem. What error messages provides move_base? Are you using amcl for localizaiton, and if so, what is the initial pose? If not 0, 0, 0, this is a probable cause of your problem, because you are telling the robot to go back to the origin of the map, not to its initial position.

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thank you, this clarifies pose vs odometry for me. I took a simpler route (for now, just a dead reckoning return to position), but I may need to return to this approach.

Really for now, all I'm trying to do is rotate the robot back to an initial position. So no lateral movement.

toddwf ( 2016-04-21 11:02:53 -0600 )edit

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