Retrotechtacular: Turn On the Magic of Colored Light

title cardChances are, you take color for granted. Whether or not you give it much thought, color is key to distinguishing your surroundings. It helps you identify fire, brown recluse spiders, and the right resistor for the job.

In the spotlight this week is a 1950s educational film called “This is Color“. It also happens to be a delightful time capsule of consumer packaging from the atomic age. This film was made by the Interchemical Corporation, an industrial research lab and manufacturer of printing inks. As the narrator explains, consistent replication of pigments is an essential part of mass production. In order to conjure a particular pigment in the first place, one must first understand the nature of color and the physical properties of visible light.

electromagnetic spectrumEach color that makes up the spectrum of visible rays has a particular wavelength. The five principal colors—red, yellow, green, blue, and violet—make possible thousands of shades and hues, but are only a small slice of the electromagnetic spectrum.

When light encounters a transparent material more dense than air, such as water or glass, it has to change direction and is bent by the surface. This is known as refraction. A straw placed in a glass of water will appear bent below the surface because the air and the water have different refractive indices. That is, the air and water will bend or refract different percentages of the light that permeates them. [Read more...]

RFID Audio Book Reader For the Visually Impaired

RFID audio book reader

When [Willem] visited home last year, he stopped in at his grandparents’ house and found that his very active 93-year-old grandfather had recently gone almost completely blind and was passing the days just sitting in a chair. [Willem] suggested that he listen to audio books, but his grandfather wasn’t receptive to the idea until [Willem] convinced him that the well-narrated ones can be very gripping and entertaining. Once his grandfather was on board, [Willem] knew that he needed a much more accessible solution than a tiny device with tiny controls, so he built an RFID audio reader using a Raspberry Pi.

[Willem] has posted the build details at his personal site. Essentially, the box you see above contains a Raspi and an RFID reader. He created different ‘books’ by placing RFID cards inside of DVD boxes, which makes them more tangible and accessible. When a book is placed on the box, the RFID reader tells the Pi which mp3 files to load. The large colored buttons let the user pause, rewind 20 seconds, and control the volume.

We love to see this kind of build. It’s simple, effective, and greatly enhances the user’s quality of life. [Willem]‘s grandfather loves it and uses it every day.

Retrotechtacular: Forces Acting On An Airfoil

floating film title We’ve probably all experimented with a very clear demonstration of the basic principles of lift: if you’re riding in a car and you put your flattened hand out the window at different angles, your hand will rise and fall like an airplane’s wing, or airfoil. This week’s Retrotechtacular explains exactly how flight is possible through the principles of lift and drag. It’s an Army training documentary from 1941 titled “Aerodynamics: Forces Acting on an Air Foil“.

What is an airfoil? Contextually speaking, it’s the shape of an airplane’s wing. In the face of pressure differences acting upon their surfaces, airfoils produce a useful aerodynamic reaction, such as the lift that makes flight possible. As the film explains, the ideas of lift and drag are measured against the yardstick of relative wind. The force of this wind on the airfoil changes according to the acute angle formed between the airfoil and the direction of the air flow acting upon it. As you may already know, lift is measured at right angles to the relative wind, and drag occurs parallel to it. Lift is opposed by the weight of the foil, and drag by tension.

wind tunnel testing

Airfoils come in several types of thicknesses and curvatures, and the film shows how a chord is derived from each shape. These chords are used to measure and describe the angle of attack in relation to the relative wind.

The forces that act upon an airfoil are measured in wind tunnels which provide straight and predictable airflow. A model airplane is supported by wires that lead to scales. These scales measure drag as well as front and rear lift.

In experimenting with angles of attack, lift and drag increase toward what is known as the stalling angle. After this point, lift decreases abruptly, and drag takes over. Lift and drag are proportional to the area of the wing, the relative wind velocity squared, and the air density. When a plane is in the air, drag is a retarding force that equals the thrust of the craft, or the propelling force.

monometer tubesAirfoil models are also unit tested in wind tunnels. They are built with small tubes running along many points of the foil that sit just under the surface. The tubes leave the model at a single point and are connected to a bank of manometer tubes. These tubes compare the pressures acting on the airfoil model to the reference point of atmospheric pressure. The different liquid levels in the manometer tubes give clear proof of the pressure values along the airfoil. These levels are photographed and mapped to a pressure curve. Now, a diagram can be made to show the positive and negative pressures relative to the angle of attack.

In closing, we are shown the effects of a dive on lift as an aircraft approaches and reaches terminal velocity, and that lift is attained again by pulling slowly out of the dive. Remember that the next time you fly your hand-plane out the window.

[Read more...]

Dampen Workshop Noise with Paper Pulp and Kool-Aid — OH YEAH!

noise dampener

If you’re fortunate enough to have a garage and a workshop, you probably also have neighbors. The truly blessed must work within the confines of an HOA that restricts noise, porch couches, and most types of fun. [Mike] is among the truly blessed, and when he decided to design a cabinet for his CNC equipment, he took noise dampening into consideration.

[Mike]‘s design isn’t a blanket noise dampener; it’s specifically designed for the high-pitch symphony of his router, compressor, and vacuum. He also sought to avoid vibrating the cabinet. To achieve this, the sound-dampening panels are hung on eye hooks with a 1/2″ gap between them and the frame. The backer boards are cut from 3/4″ plywood. [Mike] considered using cement board, but thought it might be overkill since he plants to shell the cabinet in a layer of 3/4″ plywood.

The deadening material is paper pulp made from various shredded papers. After soaking the shreds in water and blending the mixture to an oatmeal consistency, he drained most of the water through a cloth bag. Then he added just enough wood glue to hold the pulpy goo together. The tropical punch Kool-Aid powder isn’t just for looks; it provides visual confirmation of even glue distribution.

[Mike] made some tape walls around the edge of his backer boards to hold the mixture in place and painted on some wood glue to hold the pulp. He spread the tropical concoction to 1/2″ thickness with a tiling trowel to avoid compressing it. The peaks and valleys help scatter any sound that isn’t absorbed. Pudding awaits you after the jump.

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And So Castings Made of (Kinetic) Sand . . . Turn Out Pretty Well, Actually

sand castingThat kinetic sand stuff is pretty cool. It’s soft, it builds motor skills, and outside of sprinkling it on carpet, it’s not messy. If you don’t know, it’s 98% sand and 2% polydimethylsiloxane, which is a major component of Silly Putty, and according to a certain yellow and red clown, it’s safe enough to put in chicken nuggets. [Chris]‘s wife bought him some, probably because she wanted to see him play around with something that isn’t potentially deadly for a change. In the course of researching its magical properties, he found out that it doesn’t really have a thermal breakdown point, per se. At high enough temperatures, It vitrifies like a sand castle in a mushroom cloud. Between this property and its malleability, [Chris] thought he’d have a reasonable substitute for founding sand. As you can see in his latest experiment, he was right. As a bonus, he managed to turn the benign into the dangerous.

[Chris] had never cast aluminium before, so he decided to start small by making an offset cam for a rotary broach. He packed some magic sand in a wax paper cup and shoved the cam in to make the negative. Then he cut down some aluminium rod and put it in a graphite crucible. He stuck his DC arc welder’s electrode down into the crucible and cranked it up to 50A. That wasn’t enough, so he went to 110. The crucible was soon glowing orange. He carefully poured the molten aluminium into the mold. Make the jump to see how it panned out.

Spoiler alert: there’s no cussin’ this time!

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Retrotechtacular: The Voder from Bell Labs


This is the under-the-hood view of the keyboard for the Voder (Voice Operating Demonstrator), the first electronic device capable of generating continuous human speech. It accomplishes this feat through a series of keys that generate the syllables, plosives, and affricatives normally produced by the human larynx and shaped by the throat and tongue. This week’s film is a picture montage paired with the audio from the demonstration of the Voder at the 1939 World’s Fair.

The Voder was created by one [Homer Dudley] at Bell Laboratories. He did so in conjunction with the Vocoder, which analyzes human-generated speech for encrypted transfer and re-synthesizes it on the other end. [Dudley] spent over 40 years researching speech at Bell Laboratories. His development of both the Voder and the Vocoder were instrumental in the SIGSALY project which aimed to deliver encrypted voice communication to the theatres of WWII.

[Read more...]

Rolly Bot Puts a New Spin on Independent Wheel Control

rolly bot

All of [Darcy]‘s friends were making wheeled robots, so naturally, he had to make one too. His friends complicated theirs with h-bridges and casters for independent wheel maneuvering, but [Darcy] wanted something simpler. A couple of 9g servos later, the Rolly Bot was born.

Rolly Bot is self-balancing because of its low center of gravity. Should it hit a wall, the body will flip over, driving it back in the other direction. The BOM comes to a whopping $10, and that includes continuous rotation servos. It does not include the remote control capability he added later, or the cost of the CNC you would need to completely replicate this build. He even made a stand so he could test the wheels during programming.

[Darcy]‘s code is on his site along with some pictures of another version someone else built. Watch Rolly Bot roll around after the jump.

How would you make this build even simpler? Tell us in the comments.

[Read more...]


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