Pen-Dragon Mechanical Fractal-Drawing Device

[aeh5040]

Thank you very much for all the nice comments! Here are a few answers to questions.

JGW3000: I will indeed try to produce instructions at some point soon. The paper is actually an annoying issue. In the video I am using two rolls of width 3ft taped together. This is not really big enough to complete the entire 256-step curve, and it is already a nuisance to handle and to get flat enough. Really I should perhaps redesign it to make the drawing smaller, although that would require putting the wheels "inside", near the middle of the vehicle.

Gilbert Despathens, captainmib: The basic idea of a mechanical fractal-drawing machine definitely came first, and a dragon curve seemed a particularly natural choice because of the simple description, and because it looks interesting even without too many iterations. The lego implementation was by far the hardest and most time-consuming part. The Geneva mechanisms came first. There are several designs out there, but none of them quite worked well enough here - they need to be very precise and reliable, and yet have little enough friction to be able to have 6 turn each other in sequence and still have power to lift the side-arm. I'm happy with the final design for these. The motion is silky-smooth, and the 45-degree offset was achieved in a neat way. The other very hard part was the mechanism for turning a wheel by precisely one turn when triggered. I tried many many things here, including many which looked good in theory but simply didn't work, and others which worked fine "on the bench" but not under load. One just has to keep on trying different approaches. The "Armatron" design does work, and is just about reliable enough, but this in one area that could probably be improved further.

legolijnte, Mestari: As will be apparent from my youtube channel, I have a strange obsession with doing mechanically what other more more sane individuals would do with Mindstorms....

Philo: Yes, Wikipedia is your friend here - I have now added some links. You are right about the way it works: when the k-th bit of Gray code changes, exactly the first k Geneva wheels make a turn, and only the k-th one triggers the arm mechanism. Since each axle has two cams at opposite ends pointing in opposite directions, at the times when this happens it is alternately the left and right sides that get triggered. So we get a left turn or a right turn according to whether the Gray code bit is changing to a 0 or a 1, exactly as in the wikipedia description. The last axle is different - it has 3 cams on one end (at 90 degree offsets) and 1 on the other, in order to get the "twin dragon".

TinkerBrick: Yes, I think a few other curves might be possible with minimal changes - haven't thought about this properly yet. Definitely with some more extensive redesigns...

D3K: the motor is indeed working hard. It is better than the many previous designs where it would stall completely!

Victor Kojenov: it was definitely BrickCon 2012 (I didn't make it to 2013)

Edited February 18, 2014 by aeh5040

[N-4K0]

Cool machine, and cool pattern.