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Very impressive! Does it really work that reliably, or did you select the best parts for the movie?

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That's sweet! Post some pictures too so that Jim can frontpage it :)

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Very impressive! Does it really work that reliably, or did you select the best parts for the movie?

It's a lot more reliable than I expected it to be, but could still do with improvement. "Everything" took two takes because of a stuck pixel.

Really amazing! Can you post more details how you did it?

I do need to do a proper writeup of it. I came up with a very satisfying pixel mechanism, and it sort of snowballed.

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Here's a static picture of the display, showing the letter R, and the card used to program that pattern. I used white and black cones to make it a bit clearer how the pattern on the card corresponds to the pattern on the display.

17179644016_73a77576de_c.jpg

Here's a quick overview of how it works.

Each pixel looks like this:

16998047397_919ea6bff4.jpg

The vertical axles at the back are the inputs. Raising the black axle pushes the red axle over to the right; raising the white axle pushes it over to the left. This flicks the blue angle piece up or down, showing or hiding the white disk. It takes very little force, and the transition is satisfyingly quick and positive. (I recommend building one and having a play with it.)

There are 25 of these in a grid, and they sit above a matrix of push rods. The rods progressively crank inwards, to bring the 19 stud span of inputs down in to 11 studs, so they can be driven by a 6x12 plate. (I put cones between the plate studs, so it has 5x11 bits, and I leave the middle column empty to keep things nice and symmetrical.)

17204906371_cfc7fbb131.jpg

The push rods use axles with stops at the bottom. This lets me pull them down between presses - if I leave it to gravity, they sometimes get stuck in the raised position and jam the mechanism on the next press.

The fun part is the crazy pile of linkages. Here they are colour-coded to make them clearer:

17179545796_500fe0af85.jpg

The blue linkage is Chebyshev's lambda mechanism. It moves in a straight line for about half the cycle, then drops down out of the way for the return stroke. This is the bit that carries cards from the feeder (on the right) into the mechanism to be pressed up against the push rods, and simultaneously takes the card that was in the mechanism, and ejects it out the front.

The green linkage is a dwell mechanism. It remains stationary for most of the cycle, then raises the press when the card is in position, and lowers it back onto the feed rails for ejection.

The purple linkage is just raising and lowering the plate at the bottom of the push rods in a roughly sinusoidal motion, to tamp them back down between presses.

Everything's driven from the same crankshaft, so there's no annoying timing adjustments required.

The press mechanism looks like this:

16583039464_4a41224d8d.jpg

It's a straightforward rack and pinion (I wanted a design with no gears at all, but this seemed the simplest solution). I'm really including this picture because it uses my favourite technic element that isn't: The One Ring. Four of them, in fact.

I'll update later with some more video.

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I never knew the ring could be used like that.

This is overall a brilliantly executed model.

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Four rings to rule them all ...

Isn't the ring simply used as a half-width spacer?

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