

K'nex Mechanical Computer (2011) [video] - mkirsche
https://www.youtube.com/watch?v=rdT1YT9AOPA

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erroneousfunk
A couple of students from Olin College did this back in 2006/2007 with a 4-bit
adder, no electricity, no motors:
[http://knexcomputer.blogspot.com/](http://knexcomputer.blogspot.com/)

It's up in the publicly-accessible library in Needham, MA if you live nearby
and want to check it out!

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gamegoblin
Seems like a slightly more complex (has a binary -> decimal decoder) of this
[1] which was made around the same time but is a bit easier to see how it
operates (since it isn't made of K'nex)

[1]
[https://www.youtube.com/watch?v=GcDshWmhF4A](https://www.youtube.com/watch?v=GcDshWmhF4A)

I guess the big difference is the ball-drop adders don't require electricity
or motors for one calculation, but you need some method (human or otherwise)
to move the balls back to the top. Also you can only carry out calculation
downwards, so your CPU might wind up being a few hundred meters tall!

Not to disparage the ball-drop adders at all, just pointing out the
differences.

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mdonahoe
I made that project. The main benefit of balls is that the friction doesn't
add up like it does with connected rods and gears.

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rumham
This is pretty impressive. I can't imagine how much my fingers would hurt
after building that thing.

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swordswinger12
I went to high school with this guy!

