The Egg-laying Wool-Milk Pig

September 12, 2020 by Elliot Williams 32 Comments

Last week, I wrote about two recent projects of mine that serve as cautionary tales in keeping projects simple — you probably can’t simplify everything, so it’s worth the time to find out which simplifications have the most bang for the buck. This week, I’d like to share a tale of lack of design focus.

German has the eierlegende Wollmilchsau: a mystical animal that lays eggs, while producing wool, milk, and meat to boot. It’s a little bit like the English “jack of all trades, master of none” except that the eierlegende Wollmilchsau doesn’t do each job badly, it plainly can’t exist. This is obviously a bad way to start a design.

The first surfboard that I made by myself was supposed to be an eierlegende Wollmilchsau. It was going to be a longboard, because we had months with smaller waves that just weren’t all that suitable for shortboarding, but it was also going to turn sharply off the rails like a shortboard. To help it turn, it was going to have tons of camber (bend like a banana), and small fins. And along the way, I thought I’d make it thin to cut through the water.

Of course what I ended up with, not helped by my heavy fiberglassing hand, was a plow that dug into the water, would turn unexpectedly when you managed to get it onto the rails, and couldn’t pick up a small wave to save its life due to the camber and aforementioned plowing. I surfed it anyway, as a matter of pride, but I had no illusions of it being anything but the the worst board I owned. And that’s comparing it to the $30 used rasta-graphic plank that had been taking on water for at least five years, unrepaired, and was rotting out from the inside. At least it had design focus.

My surfboard didn’t suffer from feature creep, where you start piling on features until the project crumbles from overload, but rather from wanting to have my cake and eat it too. Or from failing to realize that certain design goals were necessarily tradeoffs. The “raily” behavior that I wanted when it was in bigger waves was necessarily “diggy” in small waves. Good boards trade off these features, and getting the balance between them is the art of shaping a board.

So when you start up a new project, think about which facets of your design are jointly achievable, and which are necessarily tradeoffs. Ignoring tradeoffs is a recipe for disaster, designing an eierlegende Wollmilchsau. But viewed constructively, it’s exactly these nuanced decisions that separates the simply possible from the truly marvelous. May you identify your trades, and make them well!

PLA-F Blends PLA And ABS

September 12, 2020 by Al Williams 31 Comments

In the early days of 3D printing, most people used ABS plastic. It is durable and sticks well to simple surfaces. However, it smells and emits fumes that may be dangerous. It also tends to warp as it cools which causes problems when printing. PLA smells nicer and since it is made from corn is supposed to be less noxious. However, PLA isn’t as temperature resistant and while it will stick better to beds without heat, it also requires more airflow to set the plastic as it prints. [Kerry Stevenson] recently reviewed PLA-F which is a blend of the two plastics. Is it the best of both worlds? Or the worst?

[Kerry] did several tests with interesting results. He did a temperature test tower and found the material printed well between 190 and 240 °C. He did note some stringing problems, though.

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3D POV Display Has The Shakes

September 12, 2020 by Danie Conradie 6 Comments

Persistence of vision projects are a dime a dozen, but by adding a third dimension [Madaeon] succesfully created one to stand out from the crowd. Instead of waving around a single line of LEDs, he is moving a 2D grid of them vertically to create a volumetric POV display.

The display consists of oscillating 3D printed piston, powered by a small geared motor, on top of which sits a 8 x 8 RGB LED grid and diffusing film. The motor drives a cylindrical cam, which moves a piston that sits over it, while an optical end stop detects the bottom of the piston’s travel to keep the timing correct. [Madaeon] has not added his code to the project page, but the 3D files for the mechanics are available. The current version creates a lot of vibration, but he plans to improve it by borrowing one of [Karl Bugeja]’s ideas, and using flexible PCBs and magnets.

He also links another very cool volumetric display that he constructed a few years ago. It works by projecting images from a small DLP projector onto an oscillating piece of fabric, to created some surprisingly high definition images.

POV displays are good projects for learning, so if you want to build your own, take a look a simple POV business card, or this well-documented POV spinning top.

Infinity Mirror At Warp Speed

September 11, 2020 by Brian McEvoy 10 Comments

Inventing often combines more than one old ideas into a new one. Even when the fused things are similar, the result can be more valuable than the sum of its parts. Unlike those analog watches with a digital clock below the face, when [Mojoptix] combined the re-reflecting properties of an infinity mirror with the image twisting qualities of a funhouse mirror, we get more than just a pair of mirrors. The resulting images look like a lot of fun. Warping one surface of two parallel mirrors doesn’t just alter the result a bit, because the planes feed off each other’s view, the final product is an exponentially skewed show.

Our host mounts a 3D printed ring with an hubward-facing strip of LEDs to an ordinary glass mirror. Over that, he designs four mated plates that hold semi-reflective film sheets in different shapes. The first is a hyperbolic paraboloid, but it’s probably easier to think of it as shaped like a Pringles chip (crisp). Once the light is applied, it looks like a bowtie made by a deranged god or the start of an infinite rabbit hole of light and reflection. To further the madness, he hits us with four shapes at once, so we hope you’ll take a moment to enjoy the video below.

This guy is no stranger to optics, and we’ve reported on a couple of other cool inventions that teach a concept through demonstration. His precision calipers demonstrate the Moiré effect, and his digital sundial capitalizes on parallel light beams.

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Give Me A Minute, My Eyes Are Busy

September 11, 2020 by Brian McEvoy 3 Comments

Social cues are tricky, but humans are very good at detecting where someone is looking; that goes a long way toward figuring out where someone is placing their attention. All of this goes right out the window though, when you’re talking with somebody who uses eye-tracking software to speak. [Matthew Oppenheim] with Lancaster University, UK wants to give listeners the message of Give Me a Minute with an easy-to-recognize indicator. His choice is a microBit, which displays a rotating arrow on the LED array while someone composes their speech. He chose the microBit because they are readily available, and you can get cases to fit people’s personalities. After the break, you can see a demonstration, but the graphic appears scrambled because of the screen flicker. The rotating arrow is a clear indicator that someone is writing, whereas a clock might suggest a frozen computer, and a progress bar could not be accurate.

[Matthew] wrote a program for the interpreting computer which recognizes when a message is forming by monitoring the number of black pixels in the composition field. If it changes, someone must be composing a sentence. Many people will try to peek over the speaker’s shoulder and see if they are working, but we’re sure that most readers would join the users of such tech in being unhappy if someone blatantly looks at theirr computer screen while they are typing.

Wheelchairs don’t always have to come from a hospital or supply store, and they don’t have to stay on the ground.

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Making Baseballs Go Supersonic

September 11, 2020 by Danie Conradie 31 Comments

When professional engineers are giggling like kids, you know something interesting is about to happen. [Destin Sandlin] of [Smarter Every Day], [Jeremy Fielding], and a few other like-minded individuals have built a very impressive air cannon, capable of launching baseballs at supersonic velocities.

Baseball execution. Not for sensitive viewers.

The muzzleloading canon consists of a large pressure chamber and vacuum chamber stuck together, with a plug and baseball separating the two. The barrel forms part of the vacuum chamber, and is sealed off at the muzzle end with plastic tape that ruptures when fired. The firing mechanism runs the entire length of the pressure chamber, exiting out the back where it is held in place by a large pneumatic sear mechanism. When the sear is released, it “pops the cork” between the two chambers, sending high-pressure nitrogen into the vacuum chamber, forcing the ball forward. This causes the plug rod to shoot out the back of the pressure chamber, where it is stopped by a pneumatic piston. The entire thing is permanently mounted on a trailer. A professional-looking control box is used to operate the beast from behind the safety of a steel blast shield.

Be sure to watch the videos after the break with subtitles turned on. The first is the highlights reel, and the second is a very entertaining hour-long behind the scenes look. To the surprise of the builders, they were able to shoot a baseball at Mach 1.38 (1050 mph or 1690 km/h) on the very first try, with only a partially pressurized system and a leaking vacuum chamber. When impacting the thick steel target, the ball disintegrates completely, imprinting its stitches on the target. [Destin] and co recorded the results with his usual high-speed cameras, but also included a Schlieren rig that allowed them to photograph the shock waves and Mach cones generated by the speeding ball. After a few shots, the bolts were stripped out of the pneumatic piston that stops the plug rod, which is no surprise judging by how much the steel frame flexes in that area. Continue reading “Making Baseballs Go Supersonic” →

TV Output From Arduino — 1980s Style!

September 11, 2020 by Al Williams 20 Comments

We’ll admit it, we’re all spoiled. A few bucks can now buy a computer that would have been the envy of everyone back in the late 1970s or early 1980s. So it’s no surprise that [krallja] was able to use an old-style video output chip to drive a TV with an Arduino. The TMS9918A is a venerable output device, and if the old computers could drive it then it makes sense that a modern computer could too. You can see a video of the whole experiment, below.

The Internet has also spoiled us, in that it’s dead simple to find datasheets for nearly anything, even these old chips. The only real problem with such aged silicon is that they typically expect a processor with a data and address bus, but most microcontrollers now keep all of that internal. But with enough fast I/O you can simulate a bus just fine. For now, the experiment just cycles through the color output.

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