Levitating Magnet In A Spherical Copper Cage

October 13, 2024 by Danie Conradie 21 Comments

Lenz’s Law is one of those physics tricks that look like magic if you don’t understand what’s happening. [Seth Robinson] was inspired by the way eddy currents cause a cylindrical neodymium magnet to levitate inside a rotating copper tube, so he cast a spherical copper cage to levitate a magnetic sphere.

Metal casting is an art form that might seem simple at first, but is very easy to screw up. Fortunately [Seth] has significant experience in the field, especially lost-PLA metal casting. While the act of casting is quick, the vast majority of the work is in the preparation process. Video after the break.

[Seth] started by designing and 3D printing a truncated icosahedron (basically a low-poly sphere) in two interlocking halves and adding large sprues to each halve. Over a week, the PLA forms were repeatedly coated in layers of ceramic slurry and silica sand, creating a thick shell around them. The ceramic forms were then heated to melt and pour out the PLA and fired at 870°C/1600°F to achieve full hardness.

With the molds prepared, the molten copper is poured into them and allowed to cool. To avoid damaging the soft copper parts when breaking away the mold, [Seth] uses a sandblaster to cut it away sections. The quality of the cast parts is so good that 3D-printed layer lines are visible in the copper, but hours of cleanup and polishing are still required to turn them into shiny parts. Even without the physics trick, it’s a work of art. A 3d printed plug with a brass shaft was added on each side, allowing the assembly to spin on a 3D-printed stand.

[Seth] placed a 2″ N52 neodymium spherical magnet inside, and when spun at the right speed, the magnet levitated without touching the sides. Unfortunately, this effect doesn’t come across super clearly on video, but we have no doubt it would make for a fascinating display piece and conversation starter.

Using and abusing eddy currents makes for some very interesting projects, including hoverboards and magnetic torque transfer on a bicycle.

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That’ll Go Over Like A Cement Airplane

October 8, 2024 by Al Williams 37 Comments

Most of us have made paper airplanes at one time or another, but rather than stopping at folded paper, [VirgileC] graduated to 3D printing them out of PLA. Then the obvious question is: can you cast one in cement? The answer is yes, you can, but note that the question was not: can a cement plane fly? The answer to that is no, it can’t.

Of course, you could use this to model things other than non-flying airplanes. The key is using alginate, a natural polymer derived from brown seaweed, to form the mold. The first step was to suspend the PLA model in a flowerpot with the holes blocked. Next, the flowerpot gets filled with alginate.

After a bit, you can remove the PLA from the molding material by cutting it and then reinserting it into the flower pot. However, you don’t want it to dry out completely as it tends to deform. With some vibration, you can fill the entire cavity with cement.

The next day, it was possible to destroy the alginate mold and recover the cement object inside. However, the cement will still be somewhat wet, so you’ll want to let the part dry further.

Usually, we see people print the mold directly using flexible filament. If you don’t like airplanes, maybe that’s a sign.

Automated Pixel Art With Marbles

October 6, 2024 by Danie Conradie 11 Comments

Marble machines are a fun and challenging reason to do engineering for the sake of engineering. [Engineezy] adds some color to the theme, building a machine to create 16×16 marble images automatically. (Video embedded below.)

The core problem was devising ways to sort, lift, place, and dump marbles in their correct positions without losing their marbles—figuratively and literally. Starting with color detection, [Engineezy] used an RGB color sensor and Euclidian math to determine each marble’s color. After trying several different mechanical sorting mechanisms, he settled on a solenoid and servo-actuated dump tube to drop the marble into the appropriate hopper.

After sorting, he faced challenges with designing a mechanism to transport marbles from the bottom hoppers to the top of the machine. While paddle wheels seemed promising at first, they tended to jam—a problem solved by innovating with Archimedes screws that move marbles up smoothly without clogs. The marbles are pushed into clear tubes on either side of the machine, providing a clear view of their parade to the top.

Perhaps most ingenious is his use of constant-force springs as a flexible funnel to guide the marbles to a moving slider that drops them into the correct column of the display. When a picture is complete, sliding doors open on the bottom of the columns, dumping the marbles into a chain lift which feeds them into the sorting section. Each of the mechanisms has a mirrored version of the other side, so the left and right halves of the display operate independently.

The final product is slow, satisfying and noisy kinetic testament to [Engineezy]’s perseverance through countless iterations and hiccups.

Marble machines can range from minimalist to ultra-complex musical monstrosities, but never fail to tickle our engineering minds. Continue reading “Automated Pixel Art With Marbles” →

See The “Pause-and-Attach” Technique For 3D Printing In Action

October 5, 2024 by Donald Papp 7 Comments

[3DPrintBunny] is someone who continually explores new techniques and designs in 3D printing, and her latest is one she calls “pause-and-attach”, which she demonstrates by printing a vase design with elements of the design splayed out onto the print bed.

The splayed-out elements get peeled up and attached to the print during a pause.

At a key point, the print is paused and one peels up the extended bits, manually attaching them to sockets on the main body of the print. Then the print resumes and seals everything in. The result is something that appears to defy the usual 3D printer constraints, as you can see here.

Pausing a 3D print to insert hardware (like nuts or magnets) is one thing, but we can’t recall seeing anything quite like this approach. It’s a little bit reminiscent of printing foldable structures to avoid supports in that it prints all of its own self-connecting elements, but at the same time it’s very different.

We’ve seen [3DPrintBunny]’s innovative approaches before with intentional stringing used as a design element and like the rest of her work, it’s both highly visual and definitely it’s own thing. You can see the whole process in a video she posted to social media, embedded below.

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3D Printed Jellyfish Lights Up

September 27, 2024 by Al Williams 1 Comment

[Ben] may be 15 years old, but he’s got the knack for 3D printing and artistic mechanical design. When you see his 3D-printed mechanical jellyfish lamp, we think you’ll agree. Honestly, it is hardly fair to call it a lamp. It is really — as [Ben] points out — a kinetic sculpture.

One of the high points of the post is the very detailed documentation. Not only is everything explained, but there is quite a bit of background information on jellyfish, different types of gears, and optimizing 3D prints along with information on how to recreate the sculpture.

There is quite a bit of printing, including the tentacles. There are a few options, like Arduino-controlled LEDs. However, the heart of the operation is a geared motor.

All the design files for 3D printing and the Arduino code are in the post. There’s also a remote control. The design allows you to have different colors for various pieces and easily swap them with a screwdriver.

One major concern was how noisy the thing would be with a spinning motor. According to [Ben], the noise level is about 33 dB, which is about what a whisper sounds like. However, he mentions you could consider using ball bearings, quieter motors, or different types of gears to get the noise down even further.

We imagine this jellyfish will come in at well under $6 million. If you don’t want your jellyfish to be art, maybe you’d prefer one that creates art.

Is That A Coaster? No, It’s An LED Matrix!

September 19, 2024 by Julian Scheffers 4 Comments

I’m sure you all love to see some colorful blinkenlights every now and then, and we are of course no exception. While these might look like coasters at a distance, do not be deceived! They’re actually [bitluni]’s latest project!

[bitluni]’s high-fidelity LED matrix started life as some 8×8 LED matrices lying on the shelf for 10 years taunting him – admit it, we’re all guilty of this – before he finally decided to make something with them. That idea took the form of a tileable display with the help of some magnets and pogo pins, which is certainly a very satisfying way to connect these oddly futuristic blinky coasters together.

It all starts with some schematics and a PCB. Because the CH32V208 has an annoying package to solder, [bitluni] opted to have the PCB fab do placement for him. Unfortunately, though, and like any good prototype, it needed a bodge! [bitluni] had accidentally mirrored a chip in the schematic, meaning he had to solder one of the SMD chips on upside-down, “dead bug mode”. Fortunately, the rest was seemingly more successful, because with a little 3D-printed case and some fancy programming, the tiny tiles came to life in all of their rainbow-barfing glory. Sure, the pogo pins were less reliable than desired, but [bitluni] has some ideas for a future version we’re very much looking forward to.

Video after the break.
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Creating A Twisted Grid Image Illusion With A Diffusion Model

September 18, 2024 by Maya Posch 4 Comments

Images that can be interpreted in a variety of ways have existed for many decades, with the classical example being Rubin’s vase — which some viewers see as a vase, and others a pair of human faces.

Where things get trickier is if you want to create an image that changes into something else that looks realistic when you rotate each section of it within a 3×3 grid. In a video by [Steve Mould], he explains how this can be accomplished, by using a diffusion model to identify similar characteristics of two images and to create an output image that effectively contains essential features of both images.

Naturally, this process can be done by hand too, with the goal always being to create a plausible image in either orientation that has enough detail to trick the brain into filling in the details. To head down the path of interpreting what the eye sees as a duck, a bunny, a vase or the outline of faces.

Using a diffusion model to create such illusions is quite a natural fit, as it works with filling in noise until a plausible enough image begins to appear. Of course, whether it is a viable image is ultimately not determined by the model, but by the viewer, as humans are susceptible to such illusions while machine vision still struggles to distinguish a cat from a loaf and a raisin bun from a spotted dog. The imperfections of diffusion models would seem to be a benefit here, as it will happily churn through abstractions and iterations with no understanding or interpretive bias, while the human can steer it towards a viable interpretation.

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