mechanical computation: with Merkle gates, height fields, and thread

[Ben Wiley Sittler]

Don't forget calendars and timekeeping. Those inspired several
complicated devices, including parts of the Antikythera mechanism:
https://secure.wikimedia.org/wikipedia/en/wiki/Antikythera_mechanism

On Fri, Jul 2, 2010 at 10:15, Kragen Javier Sitaker
<kragen at canonical.org> wrote:
> On Fri, Jul 02, 2010 at 03:49:55PM +0200, Dave Long wrote:
>> Le 28 juin 10 à 09:37, Kragen Javier Sitaker a écrit :
>>
>> >But braking can provide amplification. Imagine that you have a thread
>> >running along the surface of a cylinder; it can slide freely, as far
>> >as it as long as no force presses it against the cylinder. If another
>> >thread is wrapped loosely several times around the cylinder and the
>> >sliding thread, the sliding thread can still slide; but if the wrapped
>> >thread is then pulled taut, it presses the sliding thread against the
>> >cylinder, preventing it from sliding.
>>
>> if the cylinder is externally powered, a single thread suffices; when
>> it is wrapped loosely no power is coupled, but a little tension on
>> the input side produces a lot on the output side.
>
> Aha! I had forgotten about that!
>
> Considered as a part of the computation itself, it has some advantages
> and some disadvantages. The rotating cylinder won't exert much
> back-force on its drive if the thread doesn't catch, which is an
> advantage. On the other hand, it weighs thousands of times as much as a
> thread, which increases the force needed to move it at a given speed by
> thousands of times, and thus the energy at risk of dissipation.
>
> On the other hand, it may be highly practical for coupling the outputs
> from such a machine to things larger and heavier than threads. I think
> the gain of such an amplifier can be arbitrarily high, so you're limited
> only by noise.
>
>> cf differential analyzers (previous century) and capstans (previous
>> millennium) Friction-effect transhawsers?
>
> I had forgotten about C.W. Nieman's torque amplifiers used in the MIT
> differential analyzer. I never understood how they worked. Now I see, in
> the diagram here:
> <http://web.archive.org/web/20080302043939/http://www.dalefield.com/nzfmm/magazine/Differential_Analyser.html>
> Thanks for drawing the connection!
>
>> (early automated feedback applications were for windmills; I wouldn't
>> be surprised if the separation of power and control had also been
>> useful relatively early for animal-driven milling...)
>
> A friend of a friend constructed an analog automated feedback system out
> of rope and sails to keep their small sailboat on course while they were
> slept as they crossed the Caribbean.
>
> But what applications would justify a universal computing machine with
> hundreds of somewhat finicky parts before the 20th century, other than
> embedded control, even assuming you knew it could be built? Perhaps
> astrological ephemerides, cryptology, accounting, gambling, the
> computation of navigational tables, certain kinds of mathematical
> investigation such as tabulating prime numbers, perhaps long-distance
> communication.
>
> With some degree of embedded control, though, in addition to milling
> grain, you could imagine applications to the copying of books, the
> weaving of tapestries, process control in breweries and bakeries (not to
> mention other fermented foods like natto and yogurt), the irrigation of
> fields, the unattended recording of measurements, and the locking of
> doors — as well as some crude form of CNC manufacturing.
>
> How early could CNC manufacturing have been developed?
> <http://open3dp.me.washington.edu/2009/09/xtra-white-ceramic/> describes
> a recipe for 3-D printable clay: 1000 units of a white slip clay, 250
> units powdered sugar, 250 units maltodextrin.  Onto this powder you
> spray, or, presumably, drip water, to harden parts of it.  Apparently
> maltodextrin can be produced from starch by roasting with acid, by
> applying saliva, or, I think, by malting. You wouldn't need a great deal
> of dimensional accuracy or power to make useful articles out of ceramic
> in this way.
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