Exercise 4.4: Code with input runs for turn, but not for move_straight_time when I use shortcuts

[Frysti]

I made a code for the robot Summit that allows me to test what parameters have to be used to let Summit run into the room by itself. Therefore I wrote a code which allows me to enter the parameters via “input” when I run the code.
Because I didn’t want to be forced to always write out the words ‘forward’, ‘backward’, ‘clockwise’ & ‘counter-clockwise’, I defined variables for them.
For some reason though, this works for the turn, but not for the straight movement. When I run the code, there comes no error, but the robot does not move straight, yet he does turn.
If I remove my variables for forward & backward and just write them completely, it works. If I use other variables (tried fk, bk, f, g) it also does not work.

What is wrong with my variables?

from robot_control_class import RobotControl

rc = RobotControl(robot_name="summit")

a = rc.move_straight_time
b = rc.turn

fw = "forward"
bw = "backward"
cw = "clockwise"
ccw = "counter_clockwise"

a(input("forward or backward? "), float(input("what speed? ")), int(input("for how long? ")))
print (a)
b(input("clockwise or counter-clockwise? "), float(input("what speed? ")), int(input("for how long? ")))
print (b)

[ralves]

Hi @Frysti,

not knowing the definition of the move_straight_time and turn methods, it is difficult to understand exactly what your code is supposed to do.

I would recommend you put here the body of the methods aforementioned.

You can also add prints for debugging on your methods, to better understand the input values, etc.

Also, we would need to know the command you used to launch the program, and the exact inputs.

A screenshot could also help us understand you better.

[Frysti]

beginning scene:

I launched the command with python test_methods3_input.py, the script above is saved in test_methods3_input.py . Pictures folow reply-by-reply, because I’m only allowed to post one picture at a time.

This is the code of the robot_control_class.py which includes the move_straight_time and the turn method. The complete code as well as the 2 methods seperately underneath:
move_straight_time

def move_straight_time(self, motion, speed, time):

        # Initilize velocities
        self.cmd.linear.y = 0
        self.cmd.linear.z = 0
        self.cmd.angular.x = 0
        self.cmd.angular.y = 0
        self.cmd.angular.z = 0

        if motion == "forward":
            self.cmd.linear.x = speed
        elif motion == "backward":
            self.cmd.linear.x = - speed

        i = 0
        # loop to publish the velocity estimate, current_distance = velocity * (t1 - t0)
        while (i <= time):

            # Publish the velocity
            self.vel_publisher.publish(self.cmd)
            i += 1
            self.rate.sleep()

        # set velocity to zero to stop the robot
        self.stop_robot()

        s = "Moved robot " + motion + " for " + str(time) + " seconds at " + str(speed) + "  m/s"
        return s

turn

def turn(self, clockwise, speed, time):

        # Initilize velocities
        self.cmd.linear.x = 0
        self.cmd.linear.y = 0
        self.cmd.linear.z = 0
        self.cmd.angular.x = 0
        self.cmd.angular.y = 0

        if clockwise == "clockwise":
            self.cmd.angular.z = -speed
        else:
            self.cmd.angular.z = speed

        i = 0
        # loop to publish the velocity estimate, current_distance = velocity * (t1 - t0)
        while (i <= time):

            # Publish the velocity
            self.vel_publisher.publish(self.cmd)
            i += 1
            self.rate.sleep()

        # set velocity to zero to stop the robot
        self.stop_robot()

        s = "Turned robot " + clockwise + " for " + str(time) + " seconds at " + str(speed) + "  radians/second"
        return s

robot_control_class.py

#!/usr/bin/env python

import rospy
from geometry_msgs.msg import Twist
from sensor_msgs.msg import LaserScan
import time


class RobotControl():

    def __init__(self, robot_name="turtlebot"):
        rospy.init_node('robot_control_node', anonymous=True)

        if robot_name == "summit":
            rospy.loginfo("Robot Summit...")
            cmd_vel_topic = "/summit_xl_control/cmd_vel"
            # We check that sensors are working
            self._check_summit_laser_ready()
        else:      
            rospy.loginfo("Robot Turtlebot...")      
            cmd_vel_topic='/cmd_vel'
            self._check_laser_ready()

        # We start the publisher
        self.vel_publisher = rospy.Publisher(cmd_vel_topic, Twist, queue_size=1)
        self.cmd = Twist()        

        self.laser_subscriber = rospy.Subscriber(
            '/kobuki/laser/scan', LaserScan, self.laser_callback)
        self.summit_laser_subscriber = rospy.Subscriber(
            '/hokuyo_base/scan', LaserScan, self.summit_laser_callback)
        
        self.ctrl_c = False
        self.rate = rospy.Rate(1)
        rospy.on_shutdown(self.shutdownhook)

    
    def _check_summit_laser_ready(self):
        self.summit_laser_msg = None
        rospy.loginfo("Checking Summit Laser...")
        while self.summit_laser_msg is None and not rospy.is_shutdown():
            try:
                self.summit_laser_msg = rospy.wait_for_message("/hokuyo_base/scan", LaserScan, timeout=1.0)
                rospy.logdebug("Current /hokuyo_base/scan READY=>" + str(self.summit_laser_msg))

            except:
                rospy.logerr("Current /hokuyo_base/scan not ready yet, retrying for getting scan")
        rospy.loginfo("Checking Summit Laser...DONE")
        return self.summit_laser_msg

    def _check_laser_ready(self):
        self.laser_msg = None
        rospy.loginfo("Checking Laser...")
        while self.laser_msg is None and not rospy.is_shutdown():
            try:
                self.laser_msg = rospy.wait_for_message("/kobuki/laser/scan", LaserScan, timeout=1.0)
                rospy.logdebug("Current /kobuki/laser/scan READY=>" + str(self.laser_msg))

            except:
                rospy.logerr("Current /kobuki/laser/scan not ready yet, retrying for getting scan")
        rospy.loginfo("Checking Laser...DONE")
        return self.laser_msg

    def publish_once_in_cmd_vel(self):
        """
        This is because publishing in topics sometimes fails the first time you publish.
        In continuous publishing systems, this is no big deal, but in systems that publish only
        once, it IS very important.
        """
        while not self.ctrl_c:
            connections = self.vel_publisher.get_num_connections()
            if connections > 0:
                self.vel_publisher.publish(self.cmd)
                #rospy.loginfo("Cmd Published")
                break
            else:
                self.rate.sleep()

    def shutdownhook(self):
        # works better than the rospy.is_shutdown()
        self.ctrl_c = True

    def laser_callback(self, msg):
        self.laser_msg = msg

    def summit_laser_callback(self, msg):
        self.summit_laser_msg = msg

    def get_laser(self, pos):
        time.sleep(1)
        return self.laser_msg.ranges[pos]

    def get_laser_summit(self, pos):
        time.sleep(1)
        return self.summit_laser_msg.ranges[pos]

    def get_front_laser(self):
        time.sleep(1)
        return self.laser_msg.ranges[360]

    def get_laser_full(self):
        time.sleep(1)
        return self.laser_msg.ranges

    def stop_robot(self):
        #rospy.loginfo("shutdown time! Stop the robot")
        self.cmd.linear.x = 0.0
        self.cmd.angular.z = 0.0
        self.publish_once_in_cmd_vel()

    def move_straight(self):

        # Initilize velocities
        self.cmd.linear.x = 0.5
        self.cmd.linear.y = 0
        self.cmd.linear.z = 0
        self.cmd.angular.x = 0
        self.cmd.angular.y = 0
        self.cmd.angular.z = 0

        # Publish the velocity
        self.publish_once_in_cmd_vel()

    def move_straight_time(self, motion, speed, time):

        # Initilize velocities
        self.cmd.linear.y = 0
        self.cmd.linear.z = 0
        self.cmd.angular.x = 0
        self.cmd.angular.y = 0
        self.cmd.angular.z = 0

        if motion == "forward":
            self.cmd.linear.x = speed
        elif motion == "backward":
            self.cmd.linear.x = - speed

        i = 0
        # loop to publish the velocity estimate, current_distance = velocity * (t1 - t0)
        while (i <= time):

            # Publish the velocity
            self.vel_publisher.publish(self.cmd)
            i += 1
            self.rate.sleep()

        # set velocity to zero to stop the robot
        self.stop_robot()

        s = "Moved robot " + motion + " for " + str(time) + " seconds at " + str(speed) + "  m/s"
        return s


    def turn(self, clockwise, speed, time):

        # Initilize velocities
        self.cmd.linear.x = 0
        self.cmd.linear.y = 0
        self.cmd.linear.z = 0
        self.cmd.angular.x = 0
        self.cmd.angular.y = 0

        if clockwise == "clockwise":
            self.cmd.angular.z = -speed
        else:
            self.cmd.angular.z = speed

        i = 0
        # loop to publish the velocity estimate, current_distance = velocity * (t1 - t0)
        while (i <= time):

            # Publish the velocity
            self.vel_publisher.publish(self.cmd)
            i += 1
            self.rate.sleep()

        # set velocity to zero to stop the robot
        self.stop_robot()

        s = "Turned robot " + clockwise + " for " + str(time) + " seconds at " + str(speed) + "  radians/second"
        return s


if __name__ == '__main__':
    
    robotcontrol_object = RobotControl()
    try:
        robotcontrol_object.move_straight()

    except rospy.ROSInterruptException:
        pass

[Frysti]

running script:

As you can see, the robot did not move forward (same happens if I change the variables to sth else than fw or bw)…

[Frysti]

further script:

… but turned.

[Frysti]

without shortcuts:

it moves.

[ralves]

Hi @Frysti,

thanks for the screenshots.

I see in the code that you are checking if the input value is “forward” or “backward”, not “fw” or “ccw”.

Instead of defining:

fw = "forward"

and checking

if motion == "forward"

what you would need is just:

if motion == "fw"

You are confusing the name of the variable with its value.

Again: you are confusing variable name with variable value

I’m sure you will understand what I mean. If not, please read this answer again and again.
And please let us know if you managed to make the robot move accordingly.