Roomba like car
Looking to make something to clean the glass on my fishtank. My thought is to get a small car 4" large maybe? and have it act like a Roomba vacuum does. In that it would turn on for xxx amount of time during the day and drive around until it hit an edge and then it would turn and go another random direction. I would then put a magnet on the car and have a brush/scaper on the other (wet) side of the glass with a magnet of the opposite poll. This would clean the glass for me every day. Can someone point me in the right direction for this? Is there something premade out there that is a small car that moves like a roomba or can someone give me some direction on how to get there? Thanks