Philo made a great wall following LEGO bot, he writes – “As a direct application to my GP2D12 distance sensor, I built this wall follower. Its base is the Constructopedia RoverBot, I only added a turret bearing the sensor. The trick here is to direct sensor beam 45° away to also detect walls in front of vehicle. A simple program that maintains constant distance between wall and sensor creates a wall-following behaviour.” [via] – instructions and source on the site – Link.