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Crank mechansm
When you turn one end either way the other end always turns clockwise - could be used for example in a pendulum clock.
About this creation
This device is built in two separate parts, and each sort of functions without the other. Originally there was just a bottom half, and I didn't originally intend to build a top half bacause I seemed complete. But with the two tegether it is definitely better.

What the bottom half did was that when the lever was turned anticlockwise (counterclockwise), the output gear turned anticlockwise. However, when the lever was turned clockwise, the output gear didn't move. Thus if the lever happened to be a pendulum the output gear would turn every 1/2 oscillation, and always anticlockwise.

With the top half added it ensured that it wasn't stationary when the input was clockwise - it went anticlockwise whichever way the lever turned (every 1/4 pendulum oscillation). I'll explain the whole lot below.

NOTE: When the input turns anticlockwise, the output turns in the opposite direction. However, in the description above I said the output went anticlockwise. This is because that's when you look at it from the opposite end. Looking from the input end, with the lever, the output actually goes clockwise. But looking at it from that end, you can't actually see the output turning, so you turn it round and it looks like it's going clockwise. You know, like right becomes left when you look the other way.



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   The L-draw version of the top half, rendered with LDView.



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   The whole thing (real version).



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   The four small cogs are the output, the two massive ones are the input.



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   For the purpose of the explanation, when I say clockwise or anticlockwise, I mean looking at it from the input end. I'll start by explaining just the bottom half...



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   The differential gear and the output gear are both prevented by the ratchets from turning anticlockwise. When the input is turned anticlockwise...



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   ...the differential can't turn, therefore the axle at the other end of it turns in the opposie direction (clockwise)...



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   When the input is turned clockwise, the differential gear is free to turn, but only turns at half speed due to the tendency of the output to try to remain stationary...



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   Therefore when the input is turned antclockwise the output turns the other way, but when the input goes clockwise, the output doesn't move.



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   It is important to note that the output is always free to turn clockwise, due to the nature of differential gears. It just can't turn anticlockwise, because it's on a ratchet...



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   The top half works in exactly the same way, and turns when the bottom isn't turning. But since the output can always be turned clockwise by an external force the two complement each other and ensure it turns whichever way you turn the lever.



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   I'll put the L-draw model on Brickshelf in a couple of days.



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   Please don't ask for instructions. I don't think there's any point, because it's actually so simple to build.



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   The pictures should suffice.



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   This might clarify it a bit. It's just the workings of the bottom half.



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   So is this. I hope these pictures and my explanation are good enough. I'm sorry if all the anticlockwises and clockwises confused you.



Comments

 I made it 
  November 15, 2013
I'm afraid to edit this page in case I lose my Brickshelf photo links - the edit page doesn't seem to let you keep them any more and it seems like a lot of effort to add the photos again manually... Anyway check out http://www.mocpages.com/moc.php/102616 for an improved version. I'm really flattered that this guy took the time to redesign this thing (which is completely inappropriately named by the way - now I'm a qualified but non-practising engineer, I know this has nothing to do with cranks). It's probably the MOC I'm most proud of - it feels like an invention more than a model, even though I'm sure many better versions of it have existed since the start of the industrial revolution!
 I made it 
  November 15, 2013
Quoting David Hyman Yeah, kinda makes sense - should be able to work it out from the pics. Does the output turn at the same velocity for both input directions? Nice work Tom :-D
Replying nearly 8 years late (sorry!)... Yeah same speed both ways. Turns out this guy Paul S made a more compact version here (6 years ago): http://www.mocpages.com/moc.php/102616
 I like it 
  January 3, 2006
Yeah, kinda makes sense - should be able to work it out from the pics. Does the output turn at the same velocity for both input directions? Nice work Tom :-D
 
By Tom E.
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Added November 16, 2005
 


LEGO models my own creation MOCpages toys shop Crank mechansmTechnic


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