3pi not following line

I have pololu 3pi robot which is not following line on the arena drawn by the BLACK PERMANENT MARKER.

On contrary it is working pretty well on machine drawn course.

What’s wrong?
Is it reflection that affecting sensor readings?
I’m using PID code.


The line sensors on the 3pi do not detect the color of the surface directly; they measure IR reflectivity. I suspect your black permanent marker is reflecting too much of the IR light for the 3pi’s sensors to detect it properly. The 3pi-linefollower-pid example code displays the measured position on the 3pi’s LCD screen after calibration. You should be able to move the 3pi over your line and see if the displayed bar graph matches the actual position of the line (you can compare this to your machine drawn course to see the difference).

If your marker is not covering the surface well enough, you might be able to improve the performance by darkening the line. Alternatively, if that does not help, you might try using electrical tape on poster board to make your line following course, which is the way we typically prefer. You can find more information about doing this here:


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