alex35748954:
And if it's impossible for knowing how far it goes without an encoder, I'll just try right(left) hand rule instead.
Thank you for answering my questions!
Since encoders are excluded try an ultrasonic or lidar distance sensor. If you're at X and the (current) wall is Y mm away and you know the cell size, you can calculate a distance to the next intersection/turning point.
90° turns: Are you allowed to place a reflector on the walls? If so, you could add four photosensors to orient to the walls.
Just spitballin'.