Is this thumbs-up thumbs-down mechanism real?

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About as “real” as this is…


The sliding gear/glass bit would work if there was a small groove to keep it centred. Otherwise looks pretty much buildable in real life if someone felt like it.


The same motion could have been achieved without the weird sliding gear arc. Just slot the connecting rod between the crank and the gear. The connecting rod would only push / pull the gear once the pin that joins the two reaches the end of the new slot. You’d need to add some friction to the thumb shaft though, to make sure it doesn’t turn early. Totally buildable (dare I say laser cut / 3D printable).


Friction would be a problem. The sliding gear would have to be really well lubricated or the thumb will shift a little bit as the motion reverses, which I think would spoil the effect. Or they could give the axle with the thumb on it more resistance to try and hold things in place.

But I bet someone who actually understands gearing could get the same result with standard solutions. Maybe a scotch yoke system?

Which would be funny because the example actually has one of those, just not used very well.


Exactly my thought, and I build crap like that for a living. Amazing how much “mechanical theater” there is, doing things harder than they need to be just to look impressive.


Are you sure it’s intentional?

I weep for the current generation of animators who waste so much effort on making a thumb go up and down instead of some other finger.


I am more concerned about the fact that there’s no bearing support on the top gear. Just a long, spindly rod with a 90 degree bend in it.

I spend every Saturday working with middle school and high school kids building Vex robots. We discuss such subjects as supporting any rotating thing near the load. The kids get to build it wrong first, to see just how it fails. Then they appreciate the proper arrangement of moving parts much better.


Let’s build one.

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You could make the entire pie-shaped component in one piece. Just cut the teeth on the outside radius, and leave a gap at either end to get the delay for the thumb in its terminal positions. You’d need some resistance to keep the thumb from flopping over when the smaller gear disengages, but a couple of O-rings around the “thumb shaft” where it passes through the bushing would give you what you need.

The lack of support for the free end of the thumb shaft means that in real parts, the shaft will probably flop and bounce, unless it’s quite a bit bigger in diameter.


Hey Mark… Unfortunately, I don’t think it is real. It’s from a short movie called “Endless” by a Buenos Aires group called Molistudio. You can watch the full video on their website. I saw it on Vimeo.

ENDLESS is a story about seeking and not finding. It’s the mechanized routine. It’s to get up, go to work, eat, fall in love, buy, throw, fall out of love, accept, sleep, wake up. ENDLESS is a story about seeking and (not) finding.

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Not quite the same, but here’s a sweet back-and-forth intermittent mechanism YouTube user denha calls a

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Or, instead of a friction device, use small magnets at the endstops to hold the thumb in position. Less energy wasted that way. Or maybe a small cam and spring. Or a pin (or a friction brake) held in place by a cam.


Two counter-rotating gears with teeth on a small portion of their circumference would do this very simply, right?

I lack the mechanical language to articulate some other solutions that I think will give a nice, smooth movement.

Disclaimer: i’m a software engineer but I’ve played with a lot of lego and mechano in my time :wink:

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