# When Machinists Made Computers



## kquiggle (Mar 18, 2014)

Here's a link to a great article on mechanical "computers" which were used on Navy ships as recently as the 1990's. It also includes some nice videos on the mechanical principles involved.

http://arstechnica.com/information-...-mechanical-analog-computers-ruled-the-waves/

Some highlights:

" . . .the pinnacle of electromechanical analog computing: the Ford Instruments Mark 1 Fire Control computer. 

The Mark 1 weighed over 3,000 pounds. Like the Rangekeeper, it took  inputs from gun directorselectromechanically driven turret-like  barbettes with optical (and eventually radar) sensors that  continuously sent bearing and range information via electrical synchro  signals.


 The computer took into account parallax between the director and the  guns it was controlling. It also had to calculate fuse times for  mechanical fuses to ensure that the shell would explode near the target."


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## Philjoe5 (Mar 18, 2014)

Mechanical computers go wayyyyy back!  Check out 

http://en.wikipedia.org/wiki/Antikythera_mechanism

Cheers,
Phil


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## GWRdriver (Mar 18, 2014)

I didn't see a word about Charles Babbage.


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## kquiggle (Mar 19, 2014)

The article is about mechanical computers used by the U.S. Navy, so unsurprisingly there is no mention of the Antikythera mechanism or Charles Babbage, but these references do show that there is a long tradition of "mechanical computers." This could include clocks, orrerys, the Jacquard loom, adding machines, etc., depending upon your definition. However, I think few would disagree that the naval fire control computers in the article represent a pinnacle of mechanical analog computing.

What I thought might be of particular interest to members of this group is quality and variety of the machining that went into these computers, including gears, racks, cams, "slot cams," three dimensional cams (!), followers, shafts, etc., and the concepts that translate mathematical operations into mechanical movement (or vice versa).

P.S.

As an aside, I was in England recently and made a "pilgrimage" to the British Museum to see the reproduction Babbage machine there (along with many other interesting exhibits) - a beautiful piece of machinery. I understand there is a plan to connect the Babbage "difference engine" to a steam engine to drive the calculations - that will really be something to see.


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## Dale_Mahalko (Mar 27, 2016)

(I have no idea how this forum feels about digging up years-old posts, but, anyway.)

The data inputs for the early analog/mechanical computers were fed from remote data sources using a tiny type of 3-phase alternating current motor/generator known as a *Synchro motor* or *Selsyn*, which were typically about 6 inches long and about 2 inches in diameter.

Synchro motors are similar in design to modern huge 3-phase motors, but only the field coils were powered with alternating current. Depending on rotor position, the pulsating field coil induces a proportional current flow that is spread across the 3 rotor wires.

When connected to another synchro motor, whose field coils are also powered by the same AC source, the current in the 3 rotor wires in the first rotor will act to move the second rotor to exactly track and follow it.


From document cited below:






So by using a 5-wire cable system, to carry the 3-phase rotor position wires plus the single-phase field current, the rotary position of any device anywhere on a ship or submarine could be sent to anywhere else.

There isn't any particular design difference between the two synchro motors. Rotate either shaft and the other one will follow.

Turn them against each other and the current produces torque that can be "felt" across the drive wires. So it also provides a very simple form of force-feedback over the wires.


I have a couple of Synchro motors that I obtained as surplus a couple years ago. Some are still sealed in their original military steel shipping cans.


Here is a very detailed document with lots of illustrations on how Synchro motors work:

*U.S Navy Synchros - Dec 15, 1944*
Description and Operation, by RCA
http://www.maritime.org/doc/pdf/synchros.pdf


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## Tin Falcon (Mar 27, 2016)

> I have no idea how this forum feels about digging up years-old posts, but, anyway.)



As long as the post is still relevant and you are adding value to the thread it is encouraged. 
So I am guessing an early form of a servo motor? 
Tin


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## kquiggle (Mar 27, 2016)

Very interesting - and never too late to add to the discussion.

Out of curiosity, I looked on ebay: You can still buy self-synchronous motors (both new and surplus - just search for "selsyn"). Not to be confused with "synchronous motors" for clocks.


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