Services Quiz grader doubt

I have submitted the Services Quiz. I failed to pass the condition: BB8 did not move enough. Can anyone explain what this means and what I can do to rectify it?

Hello @somikdhar327 ,

It sounds like the square performed by the robot is not big enough. Try making the robot perform a bigger square (bigger radius).

I have been trying but it is still showing the same.
Here is my server code:
#! /usr/bin/env python

import rospy

from services_quiz.srv import BB8CustomServiceMessage, BB8CustomServiceMessageResponse

from geometry_msgs.msg import Twist

pub = None

def my_callback(request):

move_square = Twist()

move_square.linear.x = 0

move_square.angular.z = 0

distance = request.side

repeat = request.repetitions

wait_time = distance

while repeat > 0:


    while j < 4:

        move_square.linear.x = 0.2

        move_square.angular.z = 0



        move_square.linear.x = 0

        move_square.angular.z = 0



        move_square.linear.x = 0

        move_square.angular.z = 1.57



        move_square.linear.x = 0

        move_square.angular.z = 0



        j += 1



    repeat -= 1


my_response = BB8CustomServiceMessageResponse()

my_response.success = True

return my_response

def main():

global pub


my_service = rospy.Service('/move_bb8_in_square_custom', BB8CustomServiceMessage , my_callback) # create the Service called move_bb8_in_circle with the defined callback

pub = rospy.Publisher('/cmd_vel',Twist,queue_size = 1)

if name == ‘main’:


Is there any fault in the logic?
In the client side I have give sides as 1 and 4 for small and big square respectively.

This is my error showing in the grader

Can you share the actual behavior of the robot working with your program?
I see that the wait_time you define is the distance specified by your server. If you specify a short distance (say 0.5 meters), then the robot will only move for 0.5 seconds per side. This means that The square is probably too small.

My robot is completing the square. As you have mentioned the square may be too small. So how can I decide what time to select to make the square move for a sufficient distance?

The small square needs to be 1 sqm, and the big one 2 sqm. This is specified in the instructions. You need to figure out how much time to publish your messages in order to satisfy those dimensions.

Can you please help me out… I am stuck on the quiz related to services in ROS Basics in 5 days C++ course… Upon submission of quiz, I got “BB8 did not move enough”… I couldn’t find anything in the instructions like you have mentioned that “The small square needs to be 1 sqm, and the big one 2 sqm.” Can you please elaborate or give clear instructions for this quiz. I need this certificate badly.

Hi @talhawahab1947 , you are correct. This specification was not stated in the C++ course. I have just added it. Please let me know if you need an extra submission attempt.

@roalgoal Yes please… If you can please give back my 4 wasted submissions because i tried the same code for 4 times… And can you please confirm that the big square needs to be of 2 sqm (1.414mX1.414m)? Thank you…

I have replied you on this post:

BB8 did not move enough (Services Quiz in - Course Support / ROS Basics In 5 Days (C++) - The Construct ROS Community (

1 Like