The other day I saw a video of a guy who was pumped as hell to own a cycloid drawing machine. "What a cool thing!" I thought, "too bad it costs almost a thousands bucks!" This browser replica is free and almost identical, and that's the bad news.
This thing is ridiculously complicated! The letters at the bottom add extra gears, but there's no real pattern to where they show up or why. Moving the sliders or shrinking the gears never seems to provide the desired results. Nine times out of ten it draws stuff way outside the paper. Part way in I realised: if I can't even make a children's toy reliably draw a line, how many other things am I incapable of or totally oblivious to? So, thanks for that minor crisis, Cycloid Drawing Machine.
Despite having little to no clue how this contraption functions, I had fun screwing around with it for twenty minutes -- maybe you'll have better luck. If you give up, try messing around with this spirograph. Or don't. I'm not a cop.