Dec. 30 2019: Topics Quiz error help, Publisher & Subscriber

Course Support ROS Basics In 5 Days (Python)
1

I am not getting points for publishing to the topic “/cmd_vel” nor am I getting credit for subscribing to “/kobuki/laser/scan” even though I am doing both. The following is the code I used to submit for the quiz.

#! /usr/bin/env python

import rospy
from std_msgs.msg import Int32
from geometry_msgs.msg import Twist
from sensor_msgs.msg import LaserScan
from robot_control_class import RobotControl
rospy.init_node('topics_quiz_node')


rate = rospy.Rate(2)
var = Twist()


def turn_direction(radians):
    var.linear.x = 0.0
    var.angular.z = radians
    pub.publish(var)

def move_straight():
    var.linear.x = 0.1
    #1.5708 radians in 90degrees
    var.angular.z = 0.0
    pub.publish(var)

def stop_evaluate(ranges):
    var.linear.x = 0.0
    #1.5708 radians in 90degrees
    var.angular.z = 0.0
    pub.publish(var)

def get_max_direction_distance(ranges):
    readings = {k: v for k, v in enumerate(ranges)}
    #direction, distance,
    maxim = [0,0]
    for k,v in readings.items():
        if v > maxim[1]:
            maxim[1] = v
            maxim[0] = k
return maxim


def evaluate_direction(ranges):
    left = ranges[:360]
    center_left = ranges[350:360]
    straight = ranges[360]
    right = ranges[361:]
    center_right = ranges[361:371]
    # if min(right) < 0.3):
    #     turn_direction(1.5708* 1.8)
    # elif min(left) < 0.3):
    #     turn_direction(-1.5708* 1.8)
    if straight > 1:
        if(abs(min(center_left) - min(center_right)) > 0.3 and  max(right) > 0.9):
        #if (max(right) > 0.9):
            turn_direction(1.5708* 1.8)
        elif(abs(min(center_left) - min(center_right)) > 0.3 and  max(left) > 0.9):
        #elif(max(left) > 0.9):
            turn_direction(-1.5708* 1.8)
        else:
            move_straight()
    elif straight < 1:
        if max(right) == max(left):
            #1.5708 radians in 90degrees
            #left is positive
            #right is negative
            #turn_left
            turn_direction(1.5708* 1.8)
        elif min(right) < 1: #right side
            #turn_left
            turn_direction(1.5708 * 1.8)
        elif min(left) < 1: #left side
            #turn right
            turn_direction(-1.5708 * 1.8)

def callback(msg):                                                          
    evaluate_direction(msg.ranges)


sub = rospy.Subscriber('/kobuki/laser/scan', LaserScan, callback) 
pub = rospy.Publisher('/cmd_vel', Twist, queue_size=1)
rospy.spin()
1 Like
2

Hello @robsrandhawa,

The problem is in this line:

from robot_control_class import RobotControl

If you remove it from your code, everything will go fine. In fact, you are not using it at all.

This is because in RIA, the environment setup allows to import this class without problems. However, for the autocorrection system (specifically in this Course), the setup is not prepared for it.

Hope this helps,

3 Likes