Magnetic Gearbox Design Improvements Are Toothless But Still Cool

October 8, 2022 by Dan Maloney 9 Comments

Any project that contains something called a “flux modulator” instantly commands our attention. And while we’re pretty sure that [Retsetman] didn’t invent it after hitting his head on the toilet, this magnetic gearbox is still really cool.

Where most gearboxes have, you know, gears, a magnetic gearbox works by coupling input and output shafts not with meshing teeth but via magnetic attraction. [Retsetman]’s version has three circular elements nested together on a common axis, and while not exactly a planetary gear in the traditional sense, he still uses planetary terminology to explain how it works. The inner sun gear is a rotor with four pairs of bar magnets on its outer circumference. An outer ring gear has ten pairs of magnets, making the ratio of “teeth” between the two gears 10:2. Between these two elements is the aforementioned flux modulator, roughly equivalent to the planet gears of a traditional gearbox, with twelve grub screws around its circumference. The screws serve to conduct magnetic flux between the magnets, dragging the rotating elements along for the ride.

This gearbox appears to be a refinement on [Retsetman]’s earlier design, and while he provides no build files that we can find, it shouldn’t be too hard to roll your own designs for the printed parts.

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Iron Nitrides: Powerful Magnets Without The Rare Earth Elements

September 1, 2022 by Dan Maloney 39 Comments

Since their relatively recent appearance on the commercial scene, rare-earth magnets have made quite a splash in the public imagination. The amount of magnetic energy packed into these tiny, shiny objects has led to technological leaps that weren’t possible before they came along, like the vibration motors in cell phones, or the tiny speakers in earbuds and hearing aids. And that’s not to mention the motors in electric vehicles and the generators in wind turbines, along with countless medical, military, and scientific uses.

These advances come at a cost, though, as the rare earth elements needed to make them are getting harder to come by. It’s not that rare earth elements like neodymium are all that rare geologically; rather, deposits are unevenly distributed, making it easy for the metals to become pawns in a neverending geopolitical chess game. What’s more, extracting them from their ores is a tricky business in an era of increased sensitivity to environmental considerations.

Luckily, there’s more than one way to make a magnet, and it may soon be possible to build permanent magnets as strong as neodymium magnets, but without any rare earth metals. In fact, the only thing needed to make them is iron and nitrogen, plus an understanding of crystal structure and some engineering ingenuity.

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Falling Down The Labyrinth With Wooden Microphone Design

May 17, 2022 by Dan Maloney 7 Comments

It used to be that when we featured one of [Frank Olson]’s DIY ribbon microphone builds, it was natural to focus on the fact that he was building them almost exclusively from wood. But despite how counterintuitive it may seem, and for as many comments as we get that his microphones shouldn’t work without metal in the ribbon motors, microphones like this wooden RCA Model 77 reproduction both look and sound great.

But ironically, this homage features a critical piece that’s actually not made of wood. The 77’s pickup pattern was cardioid, making for a directional mic that picked up sound best from the front, thanks to an acoustic labyrinth that increased the path length for incoming sound waves. [Frank]’s labyrinth was made from epoxy resin poured into a mold made from heavy paper, creating a cylinder with multiple parallel tunnels. The tops and bottoms of adjacent tunnels were connected together, creating an acoustic path over a meter long. The ribbon motor, as close to a duplicate of the original as possible using wood, sits atop the labyrinth block’s output underneath a wood veneer shell that does its best to imitate the classic pill-shaped windscreen of the original. The video below, which of course was narrated using the mic, shows its construction in detail.

If you want to check out [Frank]’s other wooden microphones, and you should, check out the beautiful Model 44 replica that looks ready for [Sinatra], or the Bk-5-like mics he whipped up for drum kit recording.

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stages of moving a wire and enveloping an object

Attack Of The Magnetic Slime Robots

May 14, 2022 by Anne Ogborn 6 Comments

[Li Zhang] and his colleagues at the Chinese University of Hong Kong (CUHK) have developed a blob of goo that can navigate complex surroundings, grow an ‘arm’, grasp a wire and move it, encapsulate a small object and carry it. As explained in the research paper, the secret is in the non-Newtonian material the bots are made of.

You can make a similar concoction at home, usually called “slime”, with corn starch and water. Deformed slowly, it will move like a fluid. Deformed rapidly, it behaves like an elastic solid. CUHK’s version is polyvinyl alcohol, glass coated NdFeB microparticles (neodymium magnets), and borax.

This dual behavior lets the robot do amazing things. Placed on a surface, they made the blob extend pseudopods by dragging underneath with a magnet, then used a circular field to make it grasp and transport a wire. They used a similar technique in the other axis to swallow an object. The CUHK group are promoting this as a way to retrieve foreign objects in the body (like an accidentally swallowed button cell).

Researchers will need to develop a non-toxic coating before it can be used in the body.

Nd magnets are made by sintering Nd2O3 or NdFeB in a strong magnetic field. Nd2O3 is available from SigmaAldrich at only slightly eye watering prices. Polyvinyl alcohol and borax are easily available. This seems like a hobbyist do-able project (Nd is toxic, use precautions).

We’ve been covering micro robots for some time. Back in 2014 we covered swarm micro robots. This project uses an external field to move a small Nd magnet, and all the way back in 2014 we covered early work in this field.

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A New Wrinkle On Wooden Ribbon Microphones

March 30, 2022 by Dan Maloney 13 Comments

Not too many people build their own microphones, and those who do usually build them out of materials like plastic and metal. [Frank Olson] not only loves to make microphones, but he’s also got a thing about making them from wood, with some pretty stunning results.

[Frank]’s latest build is a sorta-kinda replica of the RCA BK-5, a classic of mid-century design. Both the original and [Frank]’s homage are ribbon microphones, in which a thin strip of corrugated metal suspended between the poles of magnets acts as a transducer. But the similarities end there, as [Frank] uses stacked layers of walnut veneer as the frame of his ribbon motor. The wood pieces are cut with a vinyl cutter, stacked up, and glued into a monolithic structure using lots of cyanoacrylate glue. The video below makes it seem easy, but we can imagine getting everything stacked neatly and lined up correctly is a chore, especially when dealing with neodymium magnets. Cutting and corrugating the aluminum foil ribbon is no mean feat either, nor is properly tensioning it and making a solid electrical contact.

The ribbon motor is suspended in a case made of yet more wood, all of which contributes to a warm, rich sound. The voice-over for the whole video below was recorded on a pair of these mics, and we think it sounds just as good as [Frank]’s earlier wooden Model 44 build. He says he has more designs in the works, and we’re looking forward to hearing them, too. Continue reading “A New Wrinkle On Wooden Ribbon Microphones” →

One Stepper Plus A Whole Bunch Of Magnets Equals A Unique Seven-Segment Display

March 5, 2022 by Dan Maloney 23 Comments

Sometimes the cost of simplicity is extra complexity. It seems counterintuitive, but it seems to be true. And this single-motor mechanical seven-segment display seems to be a perfect example of this paradox.

On second thought, [aeropic]’s mechanism isn’t really all that mechanically complicated, but there sure was a lot of planning and ingenuity that went into it. The front has a 3D-printed bezel with the familiar segment cutouts, each of which is fitted with a pivoting segment, black on one side and white on the other.

Behind the bezel is a vertical shaft with three wheels, one behind each horizontal segment, and a pair of horizontal shafts, each with two wheels behind each vertical segment. The three shafts are geared to turn together by a single stepper in the base. Each wheel has ten magnets embedded in the outer circumference, with the polarity oriented to flip the segment in front of it to the right orientation for the current digit. It’s probably something that’s most easily understood by watching the video below.

We’ve seen quite a few of these mechanical seven-segment displays lately — this cam-and-servo mechanism comes to mind. We love them all, of course, but the great thing about [aeropic]’s display is how quiet it is — the stepper is mostly silent, and the segments make only a gentle clunk when they flip. It’s very satisfying.

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Magnetic Bearings Put The Spin On This Flywheel Battery

July 22, 2021 by Dan Maloney 35 Comments

[Tom Stanton] is right about one thing: flywheels make excellent playthings. Whether watching a spinning top that never seems to slow down, or feeling the weird forces a gyroscope exerts, spinning things are oddly satisfying. And putting a flywheel to work as a battery makes it even cooler.

Of course, using a flywheel to store energy isn’t even close to being a new concept. But the principles [Tom] demonstrates in the video below, including the advantages of magnetically levitated bearings, are pretty cool to see all in one place. The flywheel itself is just a heavy aluminum disc on a shaft, with a pair of bearings on each side made of stacks of neodymium magnets. An additional low-friction thrust bearing at the end of the shaft keeps the systems suitably constrained, and allows the flywheel to spin for twelve minutes or more.

[Tom]’s next step was to harness some of the flywheel’s angular momentum to make electricity. He built a pair of rotors carrying more magnets, with a stator of custom-wound coils sandwiched between. A full-wave bridge rectifier and a capacitor complete the circuit and allow the flywheel to power a bunch of LEDs or even a small motor. The whole thing is nicely built and looks like a fun desk toy.

This is far from [Tom]’s first flywheel rodeo; his last foray into storing mechanical energy wasn’t terribly successful, but he has succeeded in making flywheels fly, one way or another.

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