Core77

Wrap Your Head Around These Gears

By Rain Noe - February 17, 2012

in Object Culture

Whether I listen to my brain, or my heart, I still
don't understand how these damn things work

When I told my Graphic Design professor that I wanted to transfer to a school offering Industrial Design, she warned me "Well, if you're going to study ID you're going to have to be able to flip things around in your head, you'll need a strong grasp of 3D." Luckily I had it, and after I made my transfer, orthographics became second nature.

That was years ago, and orthographics, of course, are not true 3D. And looking at things like cube gears makes me realize how mediocre my 3D processing abilities are.

Cube gears and heart gears, which first made a YouTube splash in 2008, have more recently been propagated by 3D-printing Thingiverse guys like emmett and faberdasher. And just when I think I'm getting my head around how they work, I come across "paradoxical gears:"

They're side by side, and yet they all turn in the same freaking direction. My brain almost broke looking at them. I figured that the guy who invented these surely used some sophisticated 3D software that artificially boosted his capabilities, like some engineering version of steroids. Then I found out it was patented way back in 1988 by a Renault engineer named Mercier. Not a lot of 3D workstations around back then (though it's possible).To make myself feel better, I dug up some videos of innovative gears that I actually can understand, as these operate in a more comprehensible two-dimensional way. Check out this gear system that changes speed:

Simple but clever. Along the same lines is this gear system that changes direction:

While I can't understand the in-video Mandarin commentary, I can understand the English comments written beneath the video. "How the f___ do you end up on videos like this?" writes one presumably bemused viewer. "I don't even remember why I came to YouTube."

o

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chris

11 years ago

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FYI: Renault has been using CAD/CAM systems since the 60's. They pretty much invented them. Search wikipedia for Pierre Bezier.

Cool article, though. Thanks!
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Pete Kirkham

12 years ago

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If you read the explanations on Jacques Maurel's website, paradoxical gears work by the teeth being on the involute of a non-crossing pulley, so are pushed in the plane not wedged by a worm out of the plane. They only mesh through some of their cycle, so you need either to layer them - http://www.youtube.com/watch?v=AwzL7Z_50zc - or build continuous layers into a helix, giving smoother operation. They aren't using the worm effect.
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Lyle

13 years ago

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The gearbox in a washing machine that makes the agitator change directions always baffled me. I wonder if it works like the "gear system that changes direction"?

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Dimitrios

13 years ago

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As with many mechanisms, it is extremely hard to understand how they work by a "top-down" approach. The shape they have becomes rather obvious when you develop them "bottom-up".
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50an6xy06r6n

13 years ago

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Yeah, the paradoxical gears are basically multi-toothed worm gears... Also for the box/heart gears it seems like they're just really beveled, and the excess part is trimmed away to form the shape.
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Andrew

13 years ago

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Looks like there might be alot of loss via friction in these?
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lin

13 years ago

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a quick translation of the chinese video (the voice over in the vid is just describing the mechanism):

this is a direction changing gear.
let's take a look.
the inner gear would first be engaged by the inner teeth, then the outer teeth, then the inner teeth again.
so hence this causes the inner gear to change its direction of rotation.
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Luke

13 years ago

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I'm no mechanical engineer, but those paradoxical gears don't look that weird. They look a lot like screws, with the one actively spinning trying to pull the other ones forward. The direction the gears spin would then be a matter of handedness. You probably only really need to take care not to have the threads lock up against each other, which I wager is why it there video isn't showing one with 20 teeth.

Here are paradoxical gears that move like regular ones:
http://www.youtube.com/watch?v=7h_Q3GmwShQ&feature

It's all probably really damn weird if you'd try and calculate their properties like ordinary toothed gears, but intuitively, they seem just fine. But then, maybe I'm completely wrong and these gears are a wisp of black magic.
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Sam E.

13 years ago

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So, I sketched and 3d-printed those paradoxical gears last week. I figured I'd get around to putting them on Thingiverse eventually. When I saw this post, I freaked out a little: "oh no, now someone is going to beat me to posting them!" So my stupid competitive spirit means you can get those paradoxical gears off Thingiverse now. http://www.thingiverse.com/thing:17746
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eren

13 years ago

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that paradoxical gear is pretty simple. think of it as if they are forcing each other down. you don't need sophisticated skills for it but it's damn cool.
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