Mechanical Analog Computers 10

[butelja]

I recently watched a documentary on battleships built during the 1930's-1940's. I was fascinated to learn that the fire control computers were 100% mechanical analog devices that considered 10 or more input variables to compute in real time the gun aiming. Does anyone know of any books that discuss mechanical analog computers? Aparently they were superior to electrical devices in the 1930's to 1950's time frame.

 

[zeitghost]

Just watched a documentary on HMS Belfast on Discovery.

It showed a reconstruction of the fire control mechanical computer in use, but without going into any detail, which was a pity.

The gunlaying information was relayed to the turrets electrically.

rgds
Zeit.

 

[zeitghost]

JAE: There was a short article on the ABC computer in the magazine "New Scientis" recently.

Very interesting and a truly prescient design.

rgds
Zeit.

 

[EnglishMuffin]

One of my favorite science fiction films of the fifties is "When Worlds Collide" (1951) - now available on DVD :

http://www.imdb.com/title/tt0044207/

There is a great shot in this film of a real differential analyzer doing the supposed orbit calculations which will confirm armageddon, and it seems to be hooked up to some sort of early pen plotter, complete with Barbara Rush in a white coat playing the obligatory "beautiful daughter of the professor" role. It's referred to as "D.A." ("send this data to D.A.&quot. It must have been state of the art for the time - possibly faster and more reliable than the digital computers of the day, and certainly far more visually impressive of course - especially for us mechanical guys. There are some other technically interesting talking points in this film, but that's another story.

 

[Aradohunter]

Does anyone have any information on the WW2 German Arado 234 jet bomber BZA computer (FuG 16zy). Code name "Egon" and used for automatic blnd bomb release during dive bombing operations. Was suppose to be quite complex for its day. Unsure if solely electronic or partly mechanical.
Regards

 

[unclesyd]

Did the Greeks invent the computer?
In the US is a show is coming on The History Channel about the "Antikythera Mechanism" discovered in Greek ship wreck.


Here is website for information on this mechanism

http://homepage.mac.com/casewright/essays/antikythera.html

 

[PSE]

The history channel show on the mechansism and a few other ancient technologies is a good one. It certainly makes you wonder where we would be now if the library in Alexandria had not been destroyed.

 

[rmw]

This thread started with the analog computers. I did my senior lab project of designing an automobile suspension that would hit a curb, and dampen the ride within an oscillation and a half on an analog computer. The "state of the art" digital computer across the campus was the size of a large room, the language was fortran, and the input was the hated punch cards. All of this was done with the trusty slide rule clipped on the hip, just in case there was a power failure. We have come a long way baby.

rmw

 

[EnglishMuffin]

Why do you say "hated punched cards" ? Of the several alternative input devices which were around at the time, (which I assume was the sixties or early seventies), cards were my favorite for programs. You could shuffle them around, add some in, leave some out etc., without having to redo the whole thing, which was not the case with paper tape or magnetic tape.

 

[SlideRuleEra]

Concur with EnglishMuffin - I was always taught to write stand alone Fortran II subroutines so that they (the cards)could be inserted into other programs "as is".
Interesting trivia on the cards themselves: When Mr. Hollerith developed the punch card system for the 1890 USA census he had to make a decision on the dimensions of the cards. He picked 7 3/8" x 3 1/4" which was the size of US paper money at that time. The money "shrank" to its' current size in 1929, but the cards are unchanged.

 

[rmw]

I just meant hated in the sense of; ever been on the way to the computer lab with a stack of text books under your arm, and on top of them a stack of punch cards, (maybe several stacks, depending upon how many problems you were working on) and somehow manage to lose your grip on all of the above, and then have to reassemble the cards (all of which happened only when you were late to the next class)???

Actually, I never used paper tape until much later, and not in computer situations, because computers were well past that, but in telex machines, which were still in vogue at the time. (ain't e-mail great??)

And, yes, it was the late '60's, and the early '70's.

rmw

 

[IRstuff]

Never touched the stuff.

Had only one class that used the IBM370, but found the WONDERFUL utility called RJE. Remote Job Entry from the PDP-10, allowing me to edit the program in a REAL editor and just shoot the stuff into the ether and get the printout from the computer desk minutes later.

AWESOME



TTFN

 

[nicabod]

Folks, discovering this Forum is a landmark event in my life; I'm now retired. I could write for days (RSI would put a stop to that!) on this topic; will try to be concise and organized. I'm jumping in with both feet and both hands; I've passionately hoped to find such a site as this since about 1986.

After one term at Princeton, when to my horror I discovered that they weren't ready for me (they still don't have a counterpart to MIT's UROP! Hope to encourage them...)
and I wasn't ready for them, either, I licked my wounds and became a Navy fire control technician. At FT school (Bainbridge, Md.), I really thought Heaven had come to earth when, well ahead of the class, I saw something with custom transparent-plastic covers replacing the cast-Al-alloy ones: it was the...

[Mark 1A mechanical analog computer:]

<

http://dcoward.best.vwh.net/analog/ford.htm>

(Doug is traveling, and looking for work, btw!)

Those pages show the WW II version, the Mark 1. (Apparently, there were different Mark 1s?) The WW II version had a mechanical resolver working backwards that didn't work too well; sometimes needed operator help. Post-war, a design re-thinking fixed that. That was the Mark 1A.

As to specs: Current consumption is apparently worst-case, all synchro receivers locked at worst-case angle. (Educated guess). The computer, itself, ought to run easily on a 20 A. 120V 60 Hz circuit.

I have a mechanical schematic of that machine, bought from Doug, which is about 19in. by 48 in. or so. I still understand maybe 2/3 of it.

===

[Web page]

One really-good Web page on the Mk.1 is at the DE220 Web site:
<

http://tinyurl.com/ljv5>,

which came from:
<

http://www.de220.com/Armament/Fire Directors/Mk 1 Computer/Mk 1 Computer.htm>

I recall reading that page some time ago, and could make some comments about it, but iirc, it's solid. No silly quasi-religious nonsense about True North.

There are some splendid National Archives images of some of the innards, although not of the really interesting sections.
Chop off the right end of the full URL some, to read a lot of very good material. Thank the site's creator!

[Btw, the 1.1-ich gun mount, also described (photos, at least) at that site, has a traverse axis; apparently it doesn't develop gimbal lock when firing straight up. IIrc, its drive servos were maintenance nightmares.]

{Repairs!]

I was extremely lucky to have occasion to repair a Mark 1A; there was a fabulous two-volume set of very-detailed instructions on disassembly, field repair (iirc), and reassembly/realignment. (HELP! Does anyone remember/know the OP number?)

We took off about 15% of the top to get at the loose screw. It was a rare treat to gently exercise the individual mechanisms, clean and lube if needed, wrap them in quite-clean rags, and put them behind the fire control switchboard.

Despite their formidable complexity, these computers were remarkably reliable; they were designed and built by very capable engineers.

===

[Misinformation, elsewhere]

There's some misinformation on the Web, as well. The integrator discs were *not* an inch thick; more like 1/4 or 3/8 inch. (Also double-sided, so they could be reversed if worn.)

The original of the article, in the Annals of the History of Computing, about Ford and Newell, has an excellent photo of an integrator. However, copies of that article do simply wretched things to the gray scale on that photo.

Also, True North, mentioned in almost religious tones on one Web site, is simply bogus. Own Ships Course was a synchro input from the gyrocompass. There was no Coriolis Effect calculation, either.

See also earlier comments about power consumption -- not really misinformation, just incompletely-defined info. (The high current was probably part of a spec. for determining power requirements and wiring for the worst case.)

===

[Some details]

The Mk. 1A has four 3-D arbitrary-function cams that hold the ballistic information for the gun and projectile the machine was built for.

The integrator outputs (through a chain of servos) drove the sights in the gun director to help keep it on target (aided tracking); tracking errors went through clutches to position the integrator carriages.

[Electromech. servos]

There's a quite-detailed description (sorry, no images) of the electromechanical position servos in the Mk.1/1A in the YahooGroups archives on the Howthingwork list, which I have contributed a great deal of material to.
It was written roughly six months ago, I think. Sorry not to have a link, now.

Really briefly, bang-bang, tungsten contacts, reversible two-phase cap.-run motor, velocity-feedback stabilized by magnetic drag* and spring. (Think high-torque-output traditional speedometer.) Large errors were stored in intermittent gearing; null was like odometers at the all-nines/all-zeros carryover.
*PM and squirrel cage, really likely

Jitter at null was minimized by flywheels on the motor shafts, free to rotate on the shafts but coupled to them by magnetic drags.

The motors were modified squirrel-cage ball-bearing induction motors with linear torque/speed curves, just about sure. They were available from Ford Instrument Co. after WW II.

As to servo bandwidth, I have no figures, but I do know that from "playing" with them that it might be as good a 10 Hz; that's a crude guess, though!

There were also a few with more-sophisticated stabilization (free flywheel connected to a differential inserted into the feedback, iirc). These had no velocity error.

===

[Photo shoot?]

I have great hopes for arranging a session (or a few) to take the covers off one of the museum-ship machines (they're too big and heavy to remove!) and take some really-good photos (scanning digital camera?) of the innards. See above for a mention...

Once done, I'd put in a few bags of dry silica gel, button it up again, maybe leave a love note to future generations, and give it a blessing.

[Materials]

Stainless steel shafts (and most gears, I assume); most of the rest, Al alloy plates. Some major mechanism support plates (Al alloy) were an inch thick, as I recall.
Housing was big Al alloy castings.

[Sounds]

The sound of these machines was distinctive and memorable. Static, there was a tinkle of gears now and then as the servos fixed tiny errors. A servo that was suddenly enabled, with a big error, made gear-train noises as it slewed and settled; full scale might take a few seconds.

The unforgettable sound, though, was that of the time motor starting and running. It took a few seconds to accelerate, with a hint of siren-like whine. Once at speed, an interesting escapement, cam, and contacts, combined with a jewel-bearing spur-gear differential did effectively a pulse-width modulation (5 Hz?) of the AC power. The torque reversals happened twice per tick (power on, power off), and were rough on the gear reduction at the motor.

The combination of the very regular "chunk-chunk", some semi-random tooth noise, and a frosting of tinkling gears was memorable. In all, maybe 60 or so (very crude guess) meshes contributed to the sound. The cast-Al alloy covers muffled some of the sound, of course.

[Range and rangefinders]

Btw, before radar, range was determined by optical rangefinders. The r/f operator turned a knob to make the target seem to be the same apparent distance away as the little open lozenge-diamonds in the reticle. (These were not split-image types; those didn't work out, in practice.)

A central wide button on the knob told the computer when the rangefinder was on target.

The view through a rangefinder was stunning. Scenes miles away seemed to be like a tabletop scale-model diorama, because the sense of depth was so strong.

Those long ears that stick out of the sides of some older gun turrets and all earlier gun directors are the ends of the rangefinder.

[Hopes]

I dearly hope to write up these machines in lots more detail on a planned Web site -- <nbodley.us> is parked, for now; nothing there (end of March, 2004).

CLASSES OF M.A. F.C. COMPUTERS

[There were essentially two main classes of mechanical analog fire-control computers. One variety, such as the Mk. 8 Range Keeper, which did just fine in 1991 for battleship shore bombardment, and the Mk.1/1A, carries computational quantities from one place to another by way or rotating shafts. Typically, full scale implies many turns of a shaft.]

[These machines, called tachymetric (not "tachometric") (Greek: "tachys" = speed, iirc), effectively determined the target speed (implicitly, I'd say). Combined with one angle, and rate of change of altitude, they defined the target motion vector.]

(For the other class, linkage, please scroll down; I'm not quite organized! )

[Prediction]

From that target-motion vector, along with range to the target, the computer could predict where the target would be when the shell reached it. The gun lead angles aimed the shell to that point, and the mechanical time fuze setting made the round explode at that time.

Yes, there were prediction multipliers, thin things, in a stack, iirc, of four. Big, too; maybe a foot square?

A simplifying assumption was that the target vector wouldn't change. (An anti-sub machine (Belock?) was built with constant radius-of-turn, as well, but that was disabled because of serious reliability problems. Don't blame Harry(?) Belock! Not his fault!)

More fun was calculating the angles required to keep the guns on target as the ship's deck tilted. Exact calculations wer not passible in the Mk.1/A; there were too many terms.
The Mk 47 Computer, mentioned below, did exact calculations, using resolver chains.

Unfortunately, these tachymetric machines were not fast enough in converging to a solution when kamikazes (late-WW II suicide bombers) came in.

[Grace Hopper]

RAdm. Grace Murray Hopper apparently did some of the fundamental math. for the (post-WW II redesign?) of the Mk. 1(A?). The Mk. 1 (WW II) design started in the early 1930s, I'm told.

[Evolution]

These tachymetric machines did evolve, however; the Computer Mk. 47, another magnificent machine, was an hybrid. It did multiplication with precision pots, and trig functions with electrical resolvers (similar to synchros). That computer was part of the GFCS Mk. 68, iirc.

The whole gun director was gyro-stabilized in one axis; it sat in a huge yoke. Trunnions were toward and away from the target. The USS Wilkinson, DL5, had that system.

A further evolution was the Computer Mk. 100 (?), for the Terrier (probably) ship-borne missile. IIrc, that computer did mostly electronically what the disk-ball-roller integrator did mechanically.

THE OTHER KIND ==================
at last

If the rotary-shaft/tachymetric variety are hard to find out about, even more obscure are the phenomenal linkage analog computers. One good look at their mechanisms, and you'll never, ever forget it.

I can only compare these to a sofa-bed linkage, or some linkages for an auto. convertible top. However, a fire control computer has more elements, and each is
by no means anywhere near to being as complicated as the two examples I cite.

I have seen two linkage computers, open to my eyes; one was in the Mk. 56, and the other was a Librascope sonar fire control computer.

[Kamikazes and the GFCS Mk.56]

The Mk 56 Gun Fire Control System was a real masterpiece. I'm essentially sure it was a very-fast-reacting system that was developed to cope with kamikazes. There are illustrations on the Web of its critical innards, very clever, and the most not-to-scale drawings I've ever seen...

However, scale drawings of its linkage computer seem exceedingly difficult to find; that's my current viewpoint. Not the least-remarkable aspect is that the ballistic calculations were done by linkages, not 3-D cams!

The Mk. 56 system's linkage computer (it had its own Mk. no.) consisted of an upper "tray" (in a casting, iirc), maybe 4 or 5 inches deep, maybe a yard (meter) wide or a little more, and maybe 20 inches from front to back. The linkage components moved sidewise; all pivot axes were straight up and down.

At the bottom of the tray were high-precision racks and pinions for rotary mechanical input and output. A substantial space below the "tray" held servos and synchros for the I/O.

There was a remarkable 3-D mechanism ('dummy gun", loosely speaking, that had a rod pointing straight down (home position). The rod fitted into a ball with a hole through it (ball: likely).

The ball moved an x-y carriage with linear-pot pickoffs, and the whole x-y assembly rotated through a limited angle as the gun director rotated around the line of sight as the deck tilted.

The assembly was nicknamed the finger of Omar.

The system design was by Ivan Getting; oral history transcripts, iirc by the IEEE, were on the Web and probably still are. One of those transcripts has the U.S. patent number on the Mk. 56 system, although there is no mention of "Mk. 56" in the patent, which was long classified. IIrc, the patent number is in the 3,400,000..3.6M range. It contains a detailed mechanical schematic, using symbols you won't easily forget.

Detailed linkage design was apparently by Antonin Svoboda, one of the authors in the MIT Radiation Lab. Series.

[Sonar linkage computer]

The sonar computer was mounted on a bulkhead (wall), and linkage movement was in a vertical plane. It was smaller than that of the Mk 56 system's computer. It contained enclosed disc-ball-roller integrators; they were on the market, once, as mechanical components.

Its sine (or cosine, but not both!) mechanisms were hypocycloidal (iirc) gears, exact 2:1 ratio between a ring gear with internal teeth, and a smaller gear on a disc crankpin, so to speak.

The inner gear rotated Spirograph fashion inside the ring, but the 2:1 ratio meant that any point on its pitch circle moved in a straight line. The output was a pivot exactly coincident with the pitch circle.

These mechanisms were also offered commercially. They were theoretically perfect, neglecting tooth errors and backlash. (This mechanism was used on some early steam engines. Don't confuse it with another somewhat-related scheme that made several flywheel rotations for one stroke.)

For just a little taste, a computer that probably did only scaled addition and subtraction, see <

http://dcoward.best.vwh.net/analog/libra.htm>.

That machine converts rotary knob inputs to linear motion, and uses cascaded "whiffletree" linkages to do scaled addition and subtraction, with the results displayed on the two large pointer dials.
(Love that spare parts collection )

Linguists will see where Librascope got its name; remember the astrological sign for Libra? Balance? ("skopein" (to see?) is Greek, iirc)

If you know the IBM Selectric mechanism (a good part of it is mechanical binary!), its tilt and rotate combining linkages are the same idea; identical in principle, except for binary inputs.

Btw, steam-engine valve gears (afaik, all) are low-accuracy analog multipliers. The Baker valve gear is closest to those used in linkage computers, although physically simpler; a Baker's castings are not the easiest to understand.

[Other personal interests; off-topic.]

Other extreme interests include mechanical calculators, with particular attention to the later Marchants, (Silent Speed) that used the proportional gears principle, essentially a 9-ratio preselector transmission for each of the ten columns(!), about 39 spur-gear differentials in the carriage, and a multi-digit *analog* magnitude comparator!!
They ran at 1,300 cycles/min. and were the speed champs for decades.

My apologies for some inconsistencies in style and editing; I'm tired, just now, and this was a piece of work! If someone as crazy as I am actually wants to edit/rearrange this, I won't mind, but I'd want to check the text.

As to factual reliability, this should be rather good. I try very hard to either be as correct as I can, or include some qualifying remarks (which, in other docs., I often do).

In closing, I am rather poor about replying to e-mail (I'd prefer to be different!), but one never knows. Try anyhow. If I'm not snowed under, I'll give my best.

Nicholas Bodley
Waltham, Mass.

 

[Skogsgurra]

Wonderful!

I'll be back to all your links many times.

 

[rmw]

Nicabod,

What a fascinating read. Thanks for sharing that with us. I did other jobs on ships, boilers, turbines, mundane things like that, and only observed the FC systems in passing. At that stage of my life, I did not have the mental capacity to understand what you just said. Now I do, and had no idea of the sophistication.

Thanks again.

rmw

 

[ScottyUK]

Nicabod,

Thanks for that epic post. It gives me an insight into things I've only seen in books or on the History Channel. Please keep posting.



-----------------------------------

Start each new day with a smile.

Get it over with.

 

[jmw]

Nicabod,
great post. Had you thought of posting it as an "FAQ"? This would be a good way to preserve your response in the fora without having to track down this thread (as mpore threads are added it will become displaced, then lost).

JMW

http://www.viscoanalyser.com

 

[nicabod]

My sincere thanks to the people who commented on that big one. You have confirmed that it's a tale worth telling. I rather hope that somebody will (unofficially?) copy it, so it doesn't get lost. (I should check Eng-Tips copyrights!)

If I ever get to the point of setting up my Web site (<nbodley.us>, which is parked at <

http://www.godaddy.com>

(it's also private, by proxy or such)), then I'll surely include at least this much.

If it's not hopelessly long, I could post this big one to FAQ, once I learn how; shouldn't be hard to do.

I do realize that a considerable amount of background has been omitted; the subject is just too big to explain in one article. I hope that the links I gave include some scanned and OCR-processed pages from a Naval training manual; that's the one that illustrates the basic F.C. mechanisms.

Best regards!

Nicholas Bodley || Eastern Mass.

 

[nicabod]

[Where did the four stars come from? I thanked the last four people for their posts...]

Anyhow, I took [jmw's] suggestion, and copied the article to the FAQ, worrying about using up space. I edited it some, fixing typos I was too tired to notice when I first wrote it. Also added some material, and restored some info (mechanical resolvers) that got lost somehow in numerous previews-and-edits in the original. However, the article is substantially the same.

My regards to all,
NB


Nicholas Bodley |*| Retired technician
Eastern Mass.

 

[PSE]

Nicabod,

The display "limit" for a posting is 4 stars, it is very likely that you have more than that from people who did not post a response directly. Enjoyable reading especially from an insider's view.

Regards,

 

[authorjim]

I am at work on my second book, about the heavy cruiser USS Houston (CA-30) lost in the Battle of Sunda Strait. Thanks to one and all for the great material on this thread. It has been tremendously useful and interesting.

In the DE220.com article linked to here

http://www.de220.com/Armament/Fire Directors/Mk 1 Computer/Mk 1 Computer.htm

it states that the Mk. 1 fire-control computer was installed in cruisers "after CL51 and CA68." This leaves me wondering about old CA-30, the Houston. Does anyone know what type of fire-control system was on the Houston? She was commissioned 17 Jun 1930.

Thanks very much.

James D. Hornfischer