Progressive Or Thrash? How Metal Detectors Discriminate

November 26, 2019 by Kristina Panos 37 Comments

Metal detecting is a fun pastime, even when all you can find is a little bit of peace and a whole lot of pop tabs. [Huygens Optics] has a VLF-based metal detector that offers much more feedback than just a beep or no beep. This thing is fancy enough to discriminate between types of metal and report back a numerical ID value from a corresponding range of conductivity.

Most pop tabs rated an ID of 76 or 77, so [Huygens Optics] started ignoring these until the day he found a platinum wedding band without looking at the ID readout. Turns out, the ring registered in the throwaway range. Now thoroughly intrigued by the detector’s ID system, [Huygens Optics] set up a test rig with an oscilloscope to see for himself how the thing was telling different metals apart. His valuable and sweeping video walk-through is hiding after the break.

A Very Low-Frequency (VLF) detector uses two coils, one to emit and one to receive. They are overlapped just enough so that the reception coil can’t see the emission coil’s magnetic field. This frees up the reception coil’s magnetic field to be interrupted only by third-party metal, i.e. hidden treasures in the ground.

Once [Huygens Optics] determined which coil was which, he started passing metal objects near the reception coil to see what happened on the ‘scope. Depending on the material type and the size and shape of the object, the waveform it produced showed a shift in phase from the emission coil’s waveform. This is pretty much directly translated to the ID readout — the higher the phase shift value, the higher the ID value.

We’ve picked up DIY metal detectors of all sizes over the years, but this one is the ATtiny-ist.

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Microphone Isolation Shield Is A Great IKEA Hack; Definitely Not A Xenomorph Egg

November 25, 2019 by Lewin Day 20 Comments

As any content creator knows, good audio is the key to maintaining an audience. Having a high quality microphone is a start, but it’s also necessary to reduce echoes and other unwanted noise. An isolation shield is key here, and [phico] has the low down on making your own.

The build starts with an IKEA lampshade, so it’s a great excuse to head down to the flatpack store and grab yourself some Köttbullar for lunch while you’re at it (that’s meatballs for those less versed in IKEA’s cafeteria fare). This is really more of a powder-coated steel frame than a shade, perfect as the bones of an enclosure. [Phico] hacks it open with a Dremel to make room for the microphone. Cardboard soaked in wallpaper paste is then used to create a papier-mache-like shell, which is then stuffed with acoustic foam. A small opening is left to allow the narrator’s voice to reach the microphone, while blocking sound from other directions. Finally, a stocking is wrapped around the whole assembly to act as an integral anti-pop filter.

Ikea BRUNSTA lampshadee

Completed ~~egg~~ isolation pod

It’s a tidy build, and while it looks a bit like a boulder to some, if you encounter a room full of ovomorphs that look just like this, tiptoe right out of there. IKEA hacks are always popular, and this laser projector lamp is a great example. If you’ve got your own nifty Swedish-inspired build, make sure you let us know!

Object Tracking Camera Slider Gets The Nice Shots

November 24, 2019 by Lewin Day 1 Comment

In this day and age, where all leisure activities must be duly captured and monetized online, camera sliders are hot items. Many start with a simple manual build, before graduating to something motorized for more flexibility. [Saral Tayal] took things a step further, implementing a basic tracking mode for even sweeter shots.

The build is mechanically simple, relying on 8mm steel rods and linear bearings more typically found in 3D printers. An Arduino Uno is pressed into service to run the show, outfitted with an OLED screen to run the interface. A RoboClaw motor controller is used to control the geared DC motors used, one controlling the linear motion, the other the rotation of the camera.

With encoders fitted to the motors, the RoboClaw controller enables the Arduino to track the position and rotation of the slider as it moves. The slider then can be given the position of an object relative to itself. With a little maths, it will rotate the camera to track the object as it moves along.

It’s a simple addition to the typical slider build that greatly increases the variety of shots that can be achieved. There are plenty of ways to go about building a slider, too, as we’ve seen before. Video after the break.
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Dambusting, R/C Style

November 23, 2019 by Dan Maloney 22 Comments

Disclaimer: no dams were actually busted in the making of the video below. But that doesn’t mean that a scale-model homage to the WWII Dam Busters and their “Bouncing Bombs” isn’t worth doing, of course.

In a war filled with hacks, [Barnes Wallis]’ Bouncing Bomb concept might just be the hackiest. In the video below, [Tom Stanton] explains that [Wallis] came up with the idea of skipping a bomb across the surface of a lake to destroy enemy infrastructure after skipping marbles across the water. Using barrel-shaped bombs, he built a rig that could give them the proper amount of backspin and release them at just the right time, letting them skip across the surface of the lake while the bomber made an escape. Upon hitting the rim of the dam, the bomb would sink to explode near the base, maximizing damage.

[Tom]’s scale rig ended up being a clever design with spring-loaded arms to release a 3D-printed barrel after being spun up by a brushless motor. He teamed up with R/C builder [James Whomsley], who came up with a wonderful foam-board Lancaster bomber, just like RAF No. 617 Squadron used. With a calm day and smooth water on the lake they chose for testing, the R/C Lanc made a few test runs before releasing the first barrel bomb. The first run was a bit too steep, causing the bomb to just dive into the water without skipping. Technical problems and a crash landing foiled the second run, but the third run was perfect – the bomb skipped thrice while the plane banked gracefully away. [Tom] also tried a heavy-lift quadcopter run with the bomb rig, something [Barnes Wallis] couldn’t even have dreamed of back in the day.

Hats off to [Tom] and [James] for collaborating on this and getting the skipping to work. It reminds us a bit of the engineered approach to rock-skipping, though with less deadly intentions.

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Advanced Techniques For Realistic Baking Animations

November 19, 2019 by Lewin Day 6 Comments

Computer graphics have come a long way since the days of Dire Straits and their first computer animated music video in 1985. To move the state of the art forward has taken the labor of countless artists, developers and technicians. Working in just that field, a group from UCLA have developed an advanced system for simulating baking in computer graphics, and the results look absolutely delicious.

We propose a porous thermo-viscoelastoplastic mixture model.

The work is being presented at SIGGRPAH Asia, and being an academic paper, is dense in arcane terminology. To properly simulate baking, the team had to consider a multitude of interdependent processes. There’s heat transfer to consider, the release of carbon dioxide from leavening agents, the browning of dough due to evaporation of water, and all manner of other complicated chemical and physical interactions.

With a model that takes all of these factors into account, the results are amazingly realistic. The team have shown off renders of cookies in the oven, freshly baked loaves of bread being torn apart, and even muffins full of melted chocolate chips.

We imagine it would have been difficult not to work up an appetite during the research process. We’ve seen impressive work from SIGGRAPH before, like this method for printing photorealistic images on 3D surfaces. Video after the break.

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Used EDM Electrodes Repurposed As Air Bearings For Precision Machine Tools

November 18, 2019 by Dan Maloney 14 Comments

If you’ve ever played air hockey, you know how the tiny jets of air shooting up from the pinholes in the playing surface reduce friction with the puck. But what if you turned that upside down? What if the puck had holes that shot the air downward? We’re not sure how the gameplay would be on such an inverse air hockey table, but [Dave Preiss] has made DIY air bearings from such a setup, and they’re pretty impressive.

Air bearings are often found in ultra-precision machine tools where nanometer-scale positioning is needed. Such gear is often breathtakingly expensive, but [Dave]’s version of the bearings used in these machines are surprisingly cheap. The working surfaces are made from slugs of porous graphite, originally used as electrodes for electrical discharge machining (EDM). The material is easily flattened with abrasives against a reference granite plate, after which it’s pressed into a 3D-printed plastic plenum. The plenum accepts a fitting for compressed air, which wends its way out the micron-sized pores in the graphite and supports the load on a thin cushion of air. In addition to puck-style planar bearings, [Dave] tried his hand at a rotary bearing, arguably more useful to precision machine tool builds. That proved to be a bit more challenging, but the video below shows that he was able to get it working pretty well.

We really enjoyed learning about air bearings from [Dave]’s experiments, and we look forward to seeing them put to use. Perhaps it will be in something like the micron-precision lathe we featured recently.

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Harmonic Analyzer Does It With Cranks And Gears

November 17, 2019 by Lewin Day 5 Comments

Before graphic calculators and microcomputers, plotting functions were generally achieved by hand. However, there were mechanical graphing tools, too. With the help of a laser cutter, it’s even possible to make your own!

The build in question is nicknamed the Harmonic Analyzer. It can be used to draw functions created by adding sine waves, a la the Fourier series. While a true Fourier series is the sum of an infinite number of sine waves, this mechanical contraption settles on just 5.

This is achieved through the use of a crank driving a series of gears. The x-axis gearing pans the notepad from left to right. The function gearing has a series of gears for each of the 5 sinewaves, which work with levers to set the magnitude of the coefficients for each component of the function. These levers are then hooked up to a spring system, which adds the outputs of each sine wave together. This spring adder then controls the y-axis motion of the pen, which draws the function on paper.

It’s a great example of the capabilities of mechanical computing, even if it’s unlikely to ever run Quake. Other DIY mechanical computers we’ve seen include the Digi-Comp I and a wildly complex Differential Analyzer. Video after the break.

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