I'd like to make a working pin tumbler lock out of LEGO bricks. I have already designed a key I'd like to use that should be compatible with five cylinder lock.

Technic Key

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    I must admit I have some doubts on the key design - the idea of the tumbler lock is that the key is a series of flats and gentle slopes so that the key pins can be pushed gently one way out of the way (against the strength of a spring, no less). I'd rather suggest two layers of 1xn plates, with 1x1 slopes above it or something. – Joubarc Nov 7 '11 at 19:40
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    Are you married to that key design? I don't see a good way to get that to slide into anything - the angle is too large and would catch the tumblers rather than push through. I would look at trying pieces like 54200 and 3044 instead, which still gives you 3 options per 2 studs = 243 possible 10 stud keys. – user23 Nov 7 '11 at 19:42
  • @Joubarc: The key is half the problem. I can see why it wouldn't work. I tried your advice, but the cheese slopes don't align themselves. – Ambo100 Nov 7 '11 at 20:15

This would push the pins up and down like a normal key would.

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Here is the basic system. I don't have time to build to whole thing but this resolves the main problem and proves the feasibility.

The main problem was to reproduce the pins system with LEGO bricks since each pins needs to have different lengths. Early in this project, I wanted to have a 'analog' approach of setting the pins length so to not be constrained by only stacking plates. For that I used axle perpendicular-joiner (6536) on an axle to build the driver pins (top pins):

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The key pins (lower pins) are caped with angles connectors (32013) creating the needed round tips on which the key can push.

In a standard pin tumbler lock system, if the right key is not pushing on the pins, both the driver pins and the key pins can prevent the rotation motion. If the key tooth is too low, the driver pins is blocking and, if the key tooth is too high, the key pin is blocking. In my system the driver pins are doing both functions.

In the prototype the red rounded beam and the driver pins would be fixed while the rest would rotating with the key. In the following picture you can see the lock without the key. In that state all the driver pins go through the black Technic beam (under the red rounded beam). This would prevent the key from turning.

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In the following picture the key is now inserted and all the driver pins are now flushed. In this position ther driver keys are not engaged into the beams that are part of the rotating module. This enables the key to turn.

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If the wrong key is used or the key is not inserted correctly, the pins would be either too low or too high engaging into the beams that are part of the rotating module and thus preventing rotation.

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Movie time! Here's a video demonstrating the mechanism.

The biggest downsides of this system are the size and the fact that the driver pins are not pushed down by spring but by gravity. Both of those troubles are put to shame by the total awesomeness of having a functioning pin tumble lock made of LEGO bricks.

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    Good demonstration, but I'd try to align the tumblers with the spot between two studs. Then you can use 3044 for a full brick height and 54200 (which you've used) for a 2/3 height, and pack 50% more tumblers in the same space. – user23 Nov 8 '11 at 0:15
  • That's the kind of design I had in mind (maybe not multicolor though ;-)). @JoeWreschnig I was assuming there was one tumbler per brick, every 8mm thus — which seems reasonable enouch to me. But a 1x1 plate instead of tile might be gentle enough to work, depending on the design of the pins. – Joubarc Nov 8 '11 at 5:11
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    @Ambo100 if you build your cylinders with rounded ends they will accept the imperfections. you could use Technic axles and cap them with a Axle Towball (2736) – pcantin Nov 8 '11 at 11:17
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    @JoeWreschnig yes, that's certainly going to be an important factor, and as a matter of fact the key and the tumbler should be designed together — even if one has ideas for keys, it's only when building the tumbler that it's possible to see if the idea will be practical or not. I'm curious enough to try it too, honestly, but I don't know when I'll find the time. – Joubarc Nov 8 '11 at 18:53
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    @Ambo100 There you go, I added an edit. – pcantin Nov 20 '11 at 16:31

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