Maybe to make sure that he is on the rank in the competition?

Because the first time it goes through, it doesn't know if it can slow down enough in time to not flip over if it takes a turn too fast. After the first run, it knows exactly how fast to go, and when it should go fast.

First run is to learn, runs afterwards are to race.

I am not an expert but based on other projects I've involved with. If you want only extremely low-speed track tracing, you probably only need several light sensors (to tell black and white) and some simple hard-coded logics (when to turn in which direction, how to navigate through the crosses). So a small customized PCB with several simple logic chips should be enough. If you want the performance in the video, you probably want to add the following functions: memory of the track, curvature calculation for maximum speed over the corners, denoising those dots at those turning points, and probably a little bit more. I don't think you need any extra sensor, but maybe a control unit similar to an Arduino is necessary to implement all these functions.

I would say some light sensor and/or something that works with reflection.

Its not necessary to be really accurate. The key is in the robot movements and memory. The first run it learns the path, the runs afterwards it races it.

array ir sensor

They are for begining and ending of the curves

@@viniciusfriasaleite8016 thank you !

The robot was designed by a Japanese, not me😅. Sorry.

我記得平井雅尊先生用的是瑞薩的微控制器。他的部落格 anikinonikki.cocolog-nifty.com/blog/