Mechanic Prince Of Tides

Lord Kelvin’s name comes up anytime you start looking at the history of science and technology. In addition to working on transatlantic cables and thermodynamics, he also built an early computing device to predict tides. Kelvin, whose real name was William Thomson, became interested in tides in a roundabout way, as explained in a recent IEEE Spectrum article.

He’d made plenty of money on his patents related to the telegraph cable, but his wife died, so he decided to buy a yacht, the Lalla Rookh. He used it as a summer home. If you live on a boat, the tides are an important part of your day.

Today, you could just ask your favorite search engine or AI about the tides, but in 1870, that wasn’t possible. Also, in a day when sea power made or broke empires, tide charts were often top secret. Not that the tides were a total mystery. Newton explained what was happening back in 1687. Laplace realized they were tied to oscillations almost a century later. Thomson made a machine that could do the math Laplace envisioned.

We know today that the tides depend on hundreds of different motions, but many of them have relatively insignificant contributions, and we only track 37 of them, according to the post. Kelvin’s machine — an intricate mesh of gears and cranks — tracked only 10 components.

In operation, the user turned a crank, and a pen traced a curve on a roll of paper. A small mark showed the hour with a special mark for noon. You could process a year’s worth of tides in about 4 hours. While Kelvin received credit for the machine’s creation, he acknowledged the help of many others in his paper, from craftsmen to his brother.

We actually did a deep dive into tides, including Kelvin’s machine, a few years ago. He shows up a number of times in our posts.

Computer Gear With — Um — Gears

Analog computers have been around in some form for a very long time. One very obvious place they were used was in military vehicles. While submarine fire computers and the Norden bombsight get all the press, [msylvain59] has a lesser-known example: an M13A1 ballistic computer from an M48 tank that he tears down for us in the video below.

The M48, known as a Patton, saw service from 1952 to 1987. Just looking at the mechanical linkage to the tank’s systems is impressive. But inside, it is clear this is a genuinely analog computer. The thing is built — quite literally — like a tank. What was the last computer you opened that needed a hammer? And inside, you’ll find gears, bearings, and a chain!

We don’t pretend to understand all the workings. These devices often used gears and synchros (or selsyns, if you prefer) to track the position of some external thing. But we are guessing there was a lot more to it than that. It’s probably an exciting process to see something like that designed from scratch.

We did think of the Norden when we saw this. Hard to imagine, but there were “general purpose” analog computers.

Continue reading “Computer Gear With — Um — Gears”

Reverse-Engineering The Mechanical Bendix Central Air Data Computer

Before the era of digital electronic computers, mechanical analog computers were found everywhere. From the relative simplicity of bomb sights to the complexity of fire control computers on 1940s battleships, all the way to 1950s fighter planes, these mechanical wonders enabled feats which were considered otherwise impossible at the time.

One such system that [Ken Shirriff] looked at a while ago is the Bendix Central Air Data Computer. As the name suggests, it is a computer system that processes air data. To be precise, it’s the mechanism found in airplanes that uses external sensor inputs to calculate parameters like altitude, vertical speed, Mach number and air speed.

Continue reading “Reverse-Engineering The Mechanical Bendix Central Air Data Computer”

A Modular Analogue Computer

We are all used to modular construction in the analogue synth world, to the extent that there’s an accepted standard for it in EuroRack. But the same techniques are just as useful wherever else analogue circuits need to be configured on the fly, such as in an analogue computer. It’s something [Rainer Glaschick] has pursued, with his Flexible Analog Computer, an analogue computer made from a set of modules mounted on breadboard strips.

Standard modules are an adder and an integrator, with the adder also having inverter, comparator, and precision rectifier functions. The various functions can be easily configured by means of jumpers, and there are digital switches on board to enable or disable outputs and inputs. he’s set up a moon landing example to demonstrate the machine in practice.

We’re not going to pretend to be analogue computer experts here at Hackaday,but we naturally welcome any foray into analogue circuitry lest it become a lost art. If you’d like to experiment with analogue computing there are other projects out there to whet your appetite, and of course they don’t even need to be electronic.

A set of solderless breadboards with op amps and their functions annotated

Op-Amp Challenge: Virtual Ball-in-a-Box Responds To Your Motions

With the incredible variety of projects submitted to our Op-Amp Contest, you’d almost forget that operational amplifiers were originally invented to perform mathematical operations, specifically inside analog computers. One popular “Hello World” kind of program for these computers is the “ball-in-a-box”, in which the computer simulates what happens when you drop a bouncy ball into a rigid box. [wlf647] has recreated this program using a handful of op amps and a classic display, and added a twist by making the system sensitive to gravity.

All the physics simulation work is performed by a set of TL072 JFET input op amps. Four are configured as integrators that simulate the motion of the ball in the X and Y directions, while four others serve as comparators that detect the ball’s collisions with the edges of the box and give it a push in the opposite direction. Three more op amps are connected to form a quadrature oscillator, which makes a set of sine and cosine waves that draw a circle representing the ball.

A miniature CRT viewfinder showing a small circleThe simulator’s output signals are connected to a tiny viewfinder CRT as well as a speaker that makes a sound whenever the ball hits one of the screen’s edges. This makes for a great ball-in-box display already, but what really makes this build special is the addition of an analog MEMS accelerometer that modifies the gravity vector in the simulation.

If you tilt or shake the sensor, the virtual box experiences a similar motion, which gives the simulation a beautiful live connection to the real world. You can see the result in a demo video [wlf647] recently posted.

The whole setup is currently sitting on a solderless breadboard, but [wlf647] is planning to integrate everything onto a PCB small enough to mount on the viewfinder, turning it into a self-contained motion simulator. Analog computers are perfect for this kind of work, and while they may seem old-fashioned, new ones are still being developed.

Inside Globus, A Soviet-Era Analog Space Computer

Whenever [Ken Shirriff] posts something, it ends up being a fascinating read. Usually it’s a piece of computer history, decapped and laid bare under his microscope where it undergoes reverse engineering and analysis to a degree that should be hard to follow, but he still somehow manages to make it understandable. And the same goes for this incredible Soviet analog flight computer, even though there’s barely any silicon inside.

The artifact in question was officially designated the “Индикатор Навигационный Космический,” which roughly translates to “space navigation indicator.” It mercifully earned the nickname “Globus” at some point, understandable given the prominent mechanized globe the device features. Globus wasn’t actually linked to any kind of inertial navigation inputs, but rather was intended to provide cosmonauts with a visual indication of where their spacecraft was relative to the surface of the Earth. As such it depended on inputs from the cosmonauts, like an initial position and orbital altitude. From there, a complicated and absolutely gorgeous gear train featuring multiple differential gears advanced the globe, showing where the spacecraft currently was.

Those of you hoping for a complete teardown will be disappointed; the device, which bears evidence of coming from the time of the Apollo-Soyuz collaboration in 1975, is far too precious to be taken to bits, and certainly looks like it would put up a fight trying to get it back together. But [Ken] still manages to go into great depth, and reveals many of its secrets. Cool features include the geopolitically fixed orbital inclination; the ability to predict a landing point from a deorbit burn, also tinged with Cold War considerations; and the instrument’s limitations, like only supporting circular orbits, which prompted cosmonauts to call for its removal. But versions of Globus nonetheless appeared in pretty much everything the Soviets flew from 1961 to 2002. Talk about staying power!

Sure, the “glass cockpit” of modern space vehicles is more serviceable, but just for aesthetics alone, we think every crewed spacecraft should sport something like Globus. [Ken] did a great job reverse-engineering this, and we really appreciate the tour. And from the sound of it, [Curious Marc] had a hand in the effort, so maybe we’ll get a video too. Fingers crossed.

Thanks to [saintaardvark] for the tip.

Circuit VR: The Wheatstone Bridge Analog Computer

We are always impressed with something so simple can actually be so complex. For example, what would you think goes into an analog computer? Of course, a “real” analog computer has opamps that can do logarithms, square roots, multiply, and divide. But would it surprise you that you can make an analog device like a slide rule using a Wheatstone bridge — essentially two voltage dividers. You don’t even need any active devices at all. It is an old idea and one that used to show up in electronic magazines now and again. I’ll show you how they work and simulate the device so you don’t have to build it unless you just want to.

A voltage divider is one of the easiest circuits in the world to analyze. Consider two resistors Ra and Rb in series. Voltage comes in at the top of Ra and the bottom of Rb is grounded. The node connecting Ra and Rb — let’s call it Z — is what we’ll consider the output.

Let’s say we have a 10 V battery feeding A and a perfect voltmeter that doesn’t load the circuit connected to Z. By Kirchoff’s current law we know the current through Ra and Rb must be the same. After all, there’s nowhere else for it to go. We also know the voltage drop across Ra plus the voltage drop across Rb must equal to 10 V. Kirchoff, conservation of energy, whatever you want to call it.  Let’s call these quantities I, Va, and Vb. Continue reading “Circuit VR: The Wheatstone Bridge Analog Computer”