Quiz corrector failed to see that I subscribed to the Topic (/kobuki/laser/scan)

Hello, I was doing the quiz (part 4 - obstacle avoidance)
I have passed the avoidance, but the quiz corrector failed to see that I subscribed to the topic required (/kobuki/laser/scan) and has deducted my points.

here is my snippet code for the subscription:

sub = rospy.Subscriber("/kobuki/laser/scan",LaserScan,callback)

What is wrong exactly?

Hey @thehitmanomar,

Sorry we somehow missed this question. Were you able to solve it?

If not, See a probably related problem (ensure you name everything as specified in the instructions):

everything is according to the instructions, I even changed the whole code structure but still the problem purists. The subscribe part is just one line of code, so I dont know how it is not getting it.

Just to chime in that I also face the same issue… I subscribed to the laser but I lost marks for “not subscribed to /kobuki/laser/scan”. Managed to avoid the obstacle.


This can happen if the node name in the launch file is not topics_quiz_node. Can you check that this is the case for you? If not, then make sure everything is named as the instructions say, it matters for the grading.


For me, the quiz corrector failed to see that I published to the /cmd_vel topic. Everything else was fine, including the obstacle avoidance. I checked using rostopic echo and saw that the program was indeed publishing to the /cmd_vel topic and reacting laser measurements of the robot. I couldn’t detect any significant difference between what I submitted and the solution that could account for this error. I named everything correctly as well.

Hi @roalgoal thanks for the tip. Not too concerned about getting everything correct right now, I am moving forward with the other units first. I will certainly be looking out for this when I review this later.

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This can happen if there’s a program running in your terminal that would be publishing to cmd_vel. Make sure you kill all programs before running the grader.

Had the same problem and this suggestion from @roalgoal fixed it for me.

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