# Are there any mechanical PID computers?

#### strantor

Joined Oct 3, 2010
5,968
My latest curiosity has me researching old mechanical devices, clockworks and such. Old mechanical computers; the Antikythera mechanism and old fire control computers. Check this out for a taste of what I'm talking about:

I want to see a mechanical implementation of PID, using the above methods (gears, shafts, cams, etc.) but I can't find much. I am aware of early pneumatic PID controllers and have posted about them before. That's not really what I'm after. I am aware of Sperry's PID controller for ships, but can't seem to find any specific information on it.

Reading up on the history of PID, I begin to wonder if by the time PID was an understood science (as opposed to an intuited one) maybe we were past the time of mechanical computing. So maybe what I want to see doesn't exist. But I thought I'd ask.

#### atferrari

Joined Jan 6, 2004
4,599
Not PID actually, but mechanical devices solving a huge amount of functions were the "tables" used to run the calculations associated with gunnery in warships. Lot of human operators (basically one for each input).

Joined Jul 18, 2013
25,232
PID for automatic steering for ships was the origins of PID control.

#### atferrari

Joined Jan 6, 2004
4,599
PID for automatic steering for ships was the origins of PID control.
Not sure if they were mechanical in any way.

#### nsaspook

Joined Aug 27, 2009
9,754
They didn't call it PID but it's the basic method of "pointer following" control inside most of the older analog computers connected to electromechanical drive systems with variable speed gearing.

https://en.wikipedia.org/wiki/Rangekeeper#Implementations_of_mathematical_functions
The implementation methods used in analog computers were many and varied. The fire control equations implemented during World War II on analog rangekeepers are the same equations implemented later on digital computers. The key difference is that the rangekeepers solved the equations mechanically. While mathematical functions are not often implemented mechanically today, mechanical methods exist to implement all the common mathematical operations. Some examples include:

Differential gears, usually referred to by technicians simply as "differentials", were often used to perform addition and subtraction operations. The Mk. 1A contained approximately 160 of them. The history of this gearing for computing dates to antiquity (see Antikythera mechanism).
Gear ratios were very extensively used to multiply a value by a constant.
• Multiplication of two variables
The Mk. 1 and Mk.1A computer multipliers were based on the geometry of similar triangles.
• Sine and cosine generation (polar-to-rectangular coordinate conversion)
These mechanisms would be called resolvers, today; they were called "component solvers" in the mechanical era. In most instances, they resolved an angle and magnitude (radius) into sine and cosine components, with a mechanism consisting of two perpendicular Scotch yokes. A variable crankpin radius handled the magnitude of the vector in question.
• Integration
Ball-and-disk integrators[23] performed the integration operation. As well, four small Ventosa integrators in the Mk. 1 and Mk. 1A computers scaled rate-control corrections according to angles.The integrators had rotating discs and a full-width roller mounted in a hinged casting, pulled down toward the disc by two strong springs. Twin balls permitted free movement of the radius input with the disk stopped, something done at least daily for static tests. Integrators were made with discs of 3, 4 and 5 inch (7.6, 10 and 12.5 cm) diameters, the larger being more accurate. Ford Instrument Company integrators had a clever mechanism for minimizing wear when the ball-carrier carriage was in one position for extended periods.
• Component integrators
Component integrators were essentially Ventosa integrators, all enclosed. Think of a traditional heavy-ball computer mouse and its pickoff rollers at right angles to each other. Underneath the ball is a roller that turns to rotate the mouse ball. However, the shaft of that roller can be set to any angle you want. In the Mk. 1/1A, a rate-control correction (keeping the sights on target) rotated the ball, and the two pickoff rollers at the sides distributed the movement appropriately according to angle. That angle depended upon the geometry of the moment, such as which way the target was heading.
Differentiation was performed by using an integrator in a feedback loop.
• Functions of one variable
Rangekeepers used a number of cams to generate function values. Many face cams (flat discs with wide spiral grooves) were used in both rangekeepers. For surface fire control (the Mk. 8 Range Keeper), a single flat cam was sufficient to define ballistics.
• Functions of two variables
In the Mk. 1 and Mk 1A computers, four three-dimensional cams were needed. These used cylindrical coordinates for their inputs, one being the rotation of the cam, and the other being the linear position of the ball follower. The radial displacement of the follower yielded the output.
The four cams in the Mk. 1/1A computer provided mechanical time fuse setting, time of flight (this time is from firing to bursting at or near the target), time of flight divided by predicted range, and superelevation combined with vertical parallax correction. (Superelevation is essentially the amount the gun barrel needs to be raised to compensate for gravity drop.)
The Mk.1 and Mk.1A computers were electromechanical, and many of their mechanical calculations required drive movements of precise speeds. They used reversible two-phase capacitor-run induction motors with tungsten contacts. These were stabilized primarily by rotary magnetic drag (eddy-current) slip clutches, similar to classical rotating-magnet speedometers, but with a much higher torque. One part of the drag was geared to the motor, and the other was constrained by a fairly stiff spring. This spring offset the null position of the contacts by an amount proportional to motor speed, thus providing velocity feedback. Flywheels mounted on the motor shafts, but coupled by magnetic drags, prevented contact chatter when the motor was at rest. Unfortunately, the flywheels must also have slowed down the servos somewhat. A more elaborate scheme, which placed a rather large flywheel and differential between the motor and the magnetic drag, eliminated velocity error for critical data, such as gun orders.

The Mk. 1 and Mk. 1A computer integrator discs required a particularly elaborate system to provide constant and precise drive speeds. They used a motor with its speed regulated by a clock escapement, cam-operated contacts, and a jeweled-bearing spur-gear differential. Although the speed oscillated slightly, the total inertia made it effectively a constant-speed motor. At each tick, contacts switched on motor power, then the motor opened the contacts again. It was in effect slow pulse-width modulation of motor power according to load. When running, the computer had a unique sound as motor power was switched on and off at each tick—dozens of gear meshes inside the cast-metal computer housing spread out the ticking into a "chunk-chunk" sound.

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#### MrChips

Joined Oct 2, 2009
26,154
A steam engine governor is some kind of controller.

#### GetDeviceInfo

Joined Jun 7, 2009
2,096
Fluidics was a growing field many years ago. The Monica was an early machine that had seen some applications. It appears that at a micro level, fluidics have a bright future.

#### strantor

Joined Oct 3, 2010
5,968
Not PID actually, but mechanical devices solving a huge amount of functions were the "tables" used to run the calculations associated with gunnery in warships. Lot of human operators (basically one for each input).
PID for automatic steering for ships was the origins of PID control.
I referred to these things in the OP. I can't find any info for the ship steering PID. Maybe there are some specific keywords I don't know to use. For the fire control (ship guns) computers I don't know that they are actually using PID, but I will dig deeper, as @nsaspook says it's basically PID; maybe PID from before they knew to call it PID.

#### atferrari

Joined Jan 6, 2004
4,599
They solved several functions.

I recall seen the integrator in action.

The old movies used for training in the US Navy had some flashes of those mechanisms. They still should be available in YT.

#### k1ng 1337

Joined Sep 11, 2020
544
That Periscope Films youtube channel is awesome. So many good videos. Fire control is a crazy thing to consider without electronics. Its interesting how the problem can be solved mechanically with high precision. They should bring back them WW2 training videos, the way they spoke back then is comedy gold. *German dummy gets shot in the head* - "He'll need more than aspirin for that head". Lol.

#### strantor

Joined Oct 3, 2010
5,968
Fire control is a crazy thing to consider without electronics. Its interesting how the problem can be solved mechanically with high precision.
I was a Fire Control Technician ("FT") on Submarines 2004-2008, so I had some familiarity with the topic before watching the video, but I still learned much from it. I had not considered that the fire control solutions for those big guns would be so much more complex than those for torpedoes. Of course it is obvious why they are, but I just hadn't given it much thought. The Fire Control system I used was all electronic. It was an old system, analog 1960s-70s tech, with patches on patches on patches until Unux computer terminals finally got installed as the front end some time before I joined (back end still banks of racks of analog cards). This Frankenstein system did very little of the work for you. I'm sure it was worlds easier to use than the system in the video, but today's newest Submarines probably track everything for you, and my old job is probably on the path to obsolescence if not already there. "Alexa, kill the bad guys."

#### k1ng 1337

Joined Sep 11, 2020
544
I was a Fire Control Technician ("FT") on Submarines 2004-2008, so I had some familiarity with the topic before watching the video, but I still learned much from it. I had not considered that the fire control solutions for those big guns would be so much more complex than those for torpedoes. Of course it is obvious why they are, but I just hadn't given it much thought. The Fire Control system I used was all electronic. It was an old system, analog 1960s-70s tech, with patches on patches on patches until Unux computer terminals finally got installed as the front end some time before I joined (back end still banks of racks of analog cards). This Frankenstein system did very little of the work for you. I'm sure it was worlds easier to use than the system in the video, but today's newest Submarines probably track everything for you, and my old job is probably on the path to obsolescence if not already there. "Alexa, kill the bad guys."
Ever have any emergencies on the vessels or seen action?

#### k1ng 1337

Joined Sep 11, 2020
544

#### Delta Prime

Joined Nov 15, 2019
1,326
Wikipedia is hardly a source to rely on and to cite. Anyone can go in and write a Wikipedia article, and that's exactly what happens.

#### nsaspook

Joined Aug 27, 2009
9,754
Ever have any emergencies on the vessels or seen action?
We ran out of fresh water at GONZO Station, I still have PTSD from those salt water showers.

#### strantor

Joined Oct 3, 2010
5,968
Ever have any emergencies on the vessels or seen action?
If you're picturing stories like in the movies, all I have to offer is disappointment. I never fired a live weapon at an enemy and I never held a pipe wrench sealing leaks to save the ship. The "action" of Submarines (in this age) is less like John Wick and more like a ninja movie where the ninja follows a target for a month straight, close enough to smell his armpits, but never pouncing and never being detected. All while suffering on the verge of hypoxia due an overtaxed oxygen generator. If you had been there I think you would agree it was "action" (at least for the first few days) but action undeserving of a feature film.

#### k1ng 1337

Joined Sep 11, 2020
544
We ran out of fresh water at GONZO Station, I still have PTSD from those salt water showers.
Hard to imagine something like that could happen with that kind of supply.

If you're picturing stories like in the movies, all I have to offer is disappointment. I never fired a live weapon at an enemy and I never held a pipe wrench sealing leaks to save the ship. The "action" of Submarines (in this age) is less like John Wick and more like a ninja movie where the ninja follows a target for a month straight, close enough to smell his armpits, but never pouncing and never being detected. All while suffering on the verge of hypoxia due an overtaxed oxygen generator. If you had been there I think you would agree it was "action" (at least for the first few days) but action undeserving of a feature film.
No disappointment here. Employing military during peace time as a deterrent force only is the best thing for a nation and its allies. Its because of this I may live my life comfortably in relative freedom. All the stuff in the movies about glory and killing is nonsense. I live in Canada and I take it you served in the US Navy? Needless to say we have it pretty good. I was asking because ships are already complex systems historically prone to killing everyone on board. I'd hate to be caught in the path of a rouge wave much less the enemy!

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#### Ya’akov

Joined Jan 27, 2019
5,696
Wikipedia is hardly a source to rely on and to cite. Anyone can go in and write a Wikipedia article, and that's exactly what happens.
That is both irrelevant and wrong. First, the value of the two linked articles is to point out the existence of various mechanisms that may fit with the question, even if there were wrong details they don’t diminish that.

Second, you must not be familiar with Wikipedia. Errors and falsehoods do not last very long, particularly on technical topics where many experts read and edit important ones particularly. But eventually, and not very long after posting, all changes are reviewed for rigor and accuracy. The system works quite well and I challenge you to find an actual example of your baseless claim.

Additionally, articles have to cite sources or they are prominently flagged as unreliable. You can read the primary sources directly for yourself.

it would help if you’d educate yourself about things before trashing them from ignorance.

#### strantor

Joined Oct 3, 2010
5,968
No disappointment here. Employing military during peace time as a deterrent force only is the best thing for a nation and its allies. Its because of this I may live my life comfortably in relative freedom. All the stuff in the movies about glory and killing is nonsense.
Agreed. I was young when I chose my rate (job) and I don't think I gave much thought to the implications of it. At least I don't remember doing so. If I did, it wasn't burdened by any wisdom of age. I'm glad I didn't have to directly take any lives.
I live in Canada and I take it you served in the US Navy?
Yes. The boat I served on is being decommissioned right now following a 33 year career.
I was asking because ships are already complex systems historically prone to killing everyone on board.
Yep. Most men who could have told stories of fighting fires, flooding, or other casualties like in the movies, didn't live to tell the tale. The only modern major Submarine casualty I'm aware of that didn't kill everyone onboard was the USS San Francisco in 2005. There are embarrassingly frequent minor casualties though. My boat was hit by a cargo ship 2 years before I reported onboard. While I was in, 2 more were hit. Last year one ran into a seamount. I remember hearing of more over the years, it's not that uncommon.