Remember the Spirograph--that drawing toy from your youth that would let you draw spiral patterns? If you have a Spirograph kit and some Lego sets sitting around, you can build a machine that will draw Spirograph patterns for you.
YouTube user Pg5200 built a Spirograph creator out of Lego Technic parts and a motor. It's super simple to use: Place a sheet of paper on an A6-sized board, insert a pen in the Lego arm, and sit back as the machine gets to work.
The Spirograph machine uses a four-speed gearbox to turn both the paper base and the arm holding the pen. The two moving pieces of hardware are adjustable, so you can alter the spiral pattern you're going for, too.
The machine is mesmerizing to watch, and the intricate patterns are almost perfectly drawn. It's easy to see why you'd get this machine to draw with a Spirograph instead, regardless of how fun it is to do yourself.