vinchuco 9 years ago

There's a one-line formula that is supposed to capture most of these motions. https://en.wikipedia.org/wiki/Hypotrochoid

What always struck me as interesting is how some of them 'seem' like they're a projection of a surface onto the plane.

Edit: In fact, it would be nice to see a 3d version where the z-axis is the angle of incidence between gears (taking one as reference).

Especially in crazier patterns with gears that are not perfect circles. Too sad this is far in the past: https://www.kickstarter.com/projects/465068187/wild-gears-20...

Note: in the starting position when you open the page, fixed 96, rotating 52. 13 revolutions for the curve to close. 52=4x13=gcd(52,96)x13

  • greeneggs 9 years ago

    You could also have a 3D spirograph where you rotate an object with an embedded "pen" around the inside of a sphere, say. It draws a 3D shape. This would be very hard to construct, but easy to simulate. Would it give you anything interesting, either as a line drawing or a surface?

    • MereInterest 9 years ago

      I'm not sure, because you would have an additional degree of freedom that needs to be constrained. With a 2D spirograph, you only have one axis of rotation. You can rotate forwards or backwards, but there are no other options. With a 3D object, there are always two possible axes of rotation. The simplest way to handle it would be to only rotate around one axis, but then you are back to just a normal 2D spirograph. There would need to be some non-linear correlation between the rotations, which adds a great deal of complexity.

      • vinchuco 9 years ago

        I think the commenter meant to have it "keep going forward" in the same manner as 2D but with some rotation involved. It's doable.

mathgenius 9 years ago

In case you think this is just a toy, have a look at what the professionals do:

https://johncarlosbaez.wordpress.com/2013/12/03/rolling-hypo...

  • ourcat 9 years ago

    Amazing. Spinors are now my new favourite things. https://en.wikipedia.org/wiki/Spinor#Introduction

    • ourcat 9 years ago

      After seeing the Spinor 'belt' animations on that page, something in my gut is screaming at me that there's some great use for this phenomenon in EMF power generation.

  • wingerlang 9 years ago

    Without more than skimming, what exactly are they doing with them? It looks just like they're making cool images without any practical purpose.

    • vinchuco 9 years ago

      "I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me."

      Isaac Newton

amelius 9 years ago

This is nice. I wrote a spirograph simulator when I was 14 years old, but of course it didn't have such nice UI (basically it was just a couple of calls of sin(x) and cos(x) in a loop, and some graphics calls, it was much fun nonetheless).

Some ideas:

- Animate the rotation of the gears more smoothly for more realism.

- Add an automatic mode, where the gears keep on moving until it reaches the point when the path starts overlapping itself.

cantrevealname 9 years ago

I like physical things and I liked the original Spirograph. But that simulator is so much easier, quicker, and more flexible. You can't even mess up by popping your pen or slipping gears.

Really, there's no reason to own a real Spirograph anymore. You might still want a Spirograph for the same reason you'd want a Curta or an Enigma, i.e., for nostalgia or as a collector's item or to behold the sheer coolness of it. But you or your kid would never play with a Spirograph today, or calculate with a Curta, or encrypt with an Enigma.

I say all this with a bit of sadness because I miss things that I could hold with my hand.

  • japhyr 9 years ago

    I completely disagree; kids learn a lot by using physical devices, that they won't learn from digital simulations. I think the best we can offer them is a mix of both.

    Physical devices develop dexterity and attention to detail. For example, drawing a circle with a compass develops a number of physical abilities. Some kids love the challenge of making neat circles of different sizes, and they'll get something out of using a compass that they'll never get from a digital circle-making tool. And keep in mind, there are different kinds of compasses. There are the pointy-tipped kind that we all think of, and there are flat ruler-types that have a spinning pivot point. Someone who's used these kinds of devices can develop a very concrete understanding of what a radius and a diameter is, among other things. I believe some of the same benefits come from working with a physical spirograph.

    Digital simulations allow people to try out many more variations in a short period of time than they could with a physical device. Digging into the code behind these simulations pushes people to understand the mathematical concepts that underlie these tools and patterns.

    Our young people can have the best of both worlds; it's our job to help them enjoy the variety of tools that are available to them today.

  • edsouza 9 years ago

    My daughter (7 years old) still plays with one, but not that often. She still enjoys it.

    We have the "Spiral Draw" by Klutz.

  • developer2 9 years ago

    >> your kid would never play with a Spirograph today

    That just represents AFK parenting. If your 5-8 year old is being babysat by the television or iPad, it is hardly their fault that they aren't experiencing anything hands-on.

  • oliyoung 9 years ago

    “you or your kid would never play with a Spirograph today”

    yeah, we would …

    • illys 9 years ago

      My daughter also spent months using one when she was 7-8, not so long ago!

Jill_the_Pill 9 years ago

I love that it will let you mess up and over-draw a line just like the real thing.

cordite 9 years ago

This would be really cool and fun for children if it worked on an iPad

nvr219 9 years ago

Couldn't stop playing with this, awesome.

sizzzzlerz 9 years ago

Very nice. A couple of suggestions:

- Add ability to move the gear by shifting its position without rotating

- Allow multiple pens

- Shift colors randomly for a pen

- Add elliptical gears

krylon 9 years ago

I had one of these as a kid, this brings up fond memories! :)

mrcactu5 9 years ago

this spirograph simulator has a really great UI.

countless, otherwise thoughtful, developers consider the User Interface as a mere "finishing touch"

Exuma 9 years ago

All my childhood nightmares come rushing back.

Kenji 9 years ago

I loved these as a kid! This brings back memories. I've never thought about the math behind it but maybe I should, this is awesome.

frozenport 9 years ago

Can you add a button that rotates the gear automatically?

  • Toadsoup 9 years ago

    The arrow keys move it. Not quite automatic but easier than the mouse.

photogrammetry 9 years ago

INB4 no meta discussions.

How long is it until literally every comment on HN is just "this is unrelated, but x."

  • DanBC 9 years ago

    In this case, however, it's a fascinating bit of work from Disney Research, and well worth watching.

  • dang 9 years ago

    The difference is that those tangents were interesting and unpredictable, where this one is unsubstantive.

    We detached this subthread from https://news.ycombinator.com/item?id=13256464 and marked it off-topic.

    • photogrammetry 9 years ago

      You're a little late. The great-grandparent post was long gone from the front page by the time you detached mine.