Retrotechtacular: The Fourier Series

Here’s a really quick video which takes a different approach to understanding the Fourier Series than we’re used to. If you’re a regular reader we’re sure you’ve heard of the Fourier Series (often discussed as FFT or Fast Fourier Transform), but there’s a good chance you know little about it. The series allows you to break down complex signals (think audio waves) into combinations of simple sine or cosine equations which can be handled by a microcontroller.

We’ve had that base level of understanding for a long time. But when you start to dig deeper we find that it becomes a math exercise that isn’t all that intuitive. The video clip embedded after the break changes that. It starts off by showing a rotating vector. Mapping the tip of that vector horizontally will draw the waveform. The Fourier Series is then leveraged, adding spinning vectors for the harmonics to the tip of the last vector. The result of summing these harmonics produces the sine-based square wave approximation seen above.

That’s a mouthful, and we’re sure you’ll agree that the video demo is much easier to understand. But the three minute clip just scratches the surface. If you’re determined to master the Fourier Series give this mammoth Stanford lecture series on the topic a try.

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Retrotechtacular: flying foot-soldiers are coming for you (sixty years ago)

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Pictured above is a remarkable piece of experimental technology from the 1950’s that never ended up going anywhere. The Hiller VZ-1 Pawnee is a single-rider vehicle that was supposed to provide a tactical advantage to US forces. The Office of Naval research spent a couple of years developing the aircraft, wich uses two rotors mounted inside the base of the platform. They spin opposite each other — which removes the need for a tail rotor like you’d find on a helicopter –to lift the platform a short distance off the ground. Although six of them were made only two survive. But the good news is you can go and see them at museums on the East or West coast of the US.

Now that the serious business is behind us, let’s talk about the video clip after the break. The narrative style is a gem of the newsreel era. We can’t tell what is going on with the accent, but we’re totally convinced that at least one general meeting per year at your local hackerspace should require all presenters to use their best impression of this talented gentleman’s voice.

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Retrotechtacular: Mechanical targeting computers

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The device that these seamen are standing around is a US Navy targeting computer. It doesn’t use electricity, but relies on mechanical computing to adjust trajectories of the ship’s guns. Setting up to twenty-five different attributes by turning cranks and other input mechanisms lets the computer automatically calculate the gun settings necessary to hit a target. These parameters include speed and heading of both the ship and it’s target, wind speed and bearing, and the location of the target in relation to this ship. It boggles the mind to think of the complexity that went into this computer.

The first of this seven part series can be seen after the break. The collection covers shafts,  gears, cams, and differentials. Sounds like it would be quite boring to sit through, huh? But as we’ve come to expect from this style and vintage of training film it packs a remarkable number of simple demonstrations into the footage.

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Retrotechtacular: Donner 3500 portable analog computer

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What if we told you we had a computer you can take with you? What if it only weighed 28 pounds? This is a pretty hard sell when today you can get a 1.5 GHz quad-core processor packing computer to carry in your pocket which weighs less than 5 ounces. But back in the day the Donner 3500 was something to raise an eyebrow at, especially for tinkerers like us.

The machine was unveiled in 1959 as an analog computer. Instead of accepting programs via a terminal, or punch cards, it worked more like a breadboard. The top of the case features a grid of connectors (they look like banana plugs to us but we’re not sure). The kit came with components which the user could plug into the top to make the machine function (or compute) in different ways.

We’re skeptical as to how portable this actually was. It used vacuum tubes which are not fans of being jostled. Still, coming during the days when most computers were taking up entire buildings we guess the marketing claim holds up. If you’d like to see a bit more about the machine’s internals check out this forum post.

Retrotechtacular: How a watch works

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Anyone who has ever tried to keep time with an electronic project will have respect for a timepiece that stays accurate over the span of months or more. We think it’s even more respectable when it comes to mechanical watches. This video was made by the Hamilton watch company back in 1949 to explain the basic processes behind a precision mechanical timepiece.

It takes several minutes to get to the meat of the presentation, but we think you’ll find the introduction just as entertaining as the explanation itself. When it does come time to look inside the watch a set of large pieces is used to help illustrate the workings of each part. The clip (which is also embedded after the break) does a great job with these demonstrations, but almost immediately you’ll come to realize the complexity wrapped up in an incredibly tiny package. It goes on to explain the low-friction properties that are brought to the table by the jewel bearings. Enjoy!

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Retrotechtacular: The differential

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Any video that starts off with two minutes of motorcycle formation riding has got to be good. If the grainy black and white video didn’t tip you off that this was made in a different time the helmetless riders standing on the seats of moving motorcycles certainly would have. But there is a purpose to this exposition. A single line of motorcycles riding shoulder to shoulder as they go around a curve illustrates why a differential is necessary and soon after you’ll find out how one works.

Two wheels mounted on one axle need to turn at different speeds as a vehicle goes around a corner or one of the wheels must slip to accommodate the speed difference. The differential is necessary to allow for these different turning rates while still letting both wheels connect to the power train. We were surprised to learn from the video after the break that early automobiles got around this issues by powering only one of the four wheels.

This instructional video is a prefect compliment to the fluid coupling video we saw in the last installment of Retrotechtacular.

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Retrotechtacular: Fluid Coupling

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We realize the transmission fluid of an automobile’s automatic transmission is used to transfer the power from the engine to the drive shaft. But after watching this Department of Defense video from 1954 we now have a full understanding of the principles involved in fluid coupling. Like us, you probably have seen a diagram of a transmission which shows the fan-like blades that are affected by the moving fluid. But it’s worth watching the 12-minute clip after the break to understand how that liquid is moving and why that matters so much in the design. The motion of the rotors, along with the design of the enclosure, causes the fluid to move in a continual corkscrew —  the shape of slinky whose ends have been attached to each other. This type of illustration leads to an intuitive understanding of how it’s possible to facilitate an efficient power transfer using a liquid.

Check out some of the comments left in the Reddit thread regarding this film. We agree with [Runxctry]; there’s something about the format of the presentation that makes these informative and engaging to an almost addictive level. But maybe it’s just the engineering geek deep inside that’s cause these feelings?

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