Thermal printer with a loop of thermochromic foil inserted in it, printing digits of Pi on the loop.The digits gradually disappear from the foil as it exits the printer.

Celebrating The Infinity Of Pi Day With Thermochromic Foil

March 21, 2022 by Arya Voronova 8 Comments

It might take you some time to understand what’s happening in the video that Hackaday alum [Moritz Sivers] shared with us. This is [Moritz]’s contribution for this year’s Pi Day – a machine that shows digits of Pi in a (technically, not quite) infinite loop, and shows us a neat trick we wouldn’t have thought of.

The two main elements of this machine are a looped piece of thermochromic foil and a thermal printer. As digits are marked on the foil by the printer’s heating element, they’re visible for a few seconds until the foil disappears from the view, only to be eventually looped back and thermally embossed anew. The “Pi digits calculation” part is offloaded to Google’s pi.delivery service, a π-as-a-Service endpoint that will stream up to 50 trillion first digits of Pi in case you ever need them – an ESP8266 dutifully fetches the digits and sends them off to the thermal printer.

This machine could print the digits until something breaks or the trillions of digits available run out, and is an appropriate tribute to the infinite nature of Pi, a number we all have no choice but to fundamentally respect. A few days ago, we’ve shown a similar Pi Day tribute, albeit a more self-sufficient one – an Arduino calculating and printing digits of Pi on a character display! We could’ve been celebrating this day for millennia, if Archimedes could just count a little better.

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Throttle Your Solid Rocket Motors With This One Simple Trick!

March 18, 2022 by Ryan Flowers 14 Comments

For decades, mankind was content to launch payloads into orbit and then watch hundreds of thousands of hours of blood sweat and tears just crash into the ocean. Then, partially because of huge advancements in being able to throttle rocket engines, we started landing our first stage boosters. [Joe] over at the BPS.space YouTube channel is tired of watching SpaceX have all the booster landing fun, but he’s not quite at the throttled liquid engine stage yet. So in the video below the break he asked the question: Can you throttle solid rocket motors? Yes. No. Sort of.

Throttling liquid rocket engines is actually not that different from throttling any other engine- by limiting the amount of fuel and oxidizer. This is challenging all on its own because well… it’s rocket science. With liquid rocket engines though, the concept is at least straightforward. But model rocketry hobbyists only use liquid fueled engines on the extreme high end. The vast majority instead use solid fueled rockets where the fuel is pre-mixed and isn’t variable at all.

These obvious hurdles didn’t stop [Joe] from trying. And trying again. Then, again. And once more for good measure. And then again for repeatability. There are definitely some failures along the way, and we applaud [Joe] for even admitting that he didn’t know how to use a drill properly. Hackers of any age can relate to the time when the didn’t know how to do something, although we also tend to not talk about that part too much.

We won’t spoil the ending except to say that the video is definitely worth a watch to see how [Joe] essentially solves the problem of limiting the effective thrust of a solid rocket engine without actually throttling the engine, and learns about a new issue he’d never seen before.

Of course you can also make rocket engines at home out of a plethora of ingredients, just be sure to do it in somebody else’s kitchen!

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3D Printed Molds For Casting Rose’s Metal

March 17, 2022 by Kristina Panos 21 Comments

Have you ever played with Rose’s metal? It’s a fusible alloy of bismuth, lead, and tin with a low melting point of around 100 °C. Historically, it’s been used as a solder for cast iron railings and things, and as a malleable pipe filler material to prevent crimping while a pipe is bent.

[Ben Healey] has been playing around with Rose’s metal and some PETG printed molds, making everything from Star Wars Imperial credits to chess pieces to leather stamping tools. In the video after the break, [Ben] takes us through the process, beginning with mold-making from STLs — something he picked up from another YouTuber.

He recommends adding registration marks to multi-part molds in order to keep everything lined up, and adding a small recess in the seam for easy separation with a flat-head screwdriver. So far, the molds have held up to multiple pours, though [Ben] did print them rather thick and is glad he did.

As far as making liquid metal, [Ben] used a cast iron pot with a convenient pour spout, and a blowtorch. He added graphite powder to the molds in an effort to make them give up the goods more easily. To finish the pieces, [Ben] cut the flashing with tin snips and used sandpaper and a Dremel to smooth the edges. Copper plating didn’t work out, but [Ben] is going to try it again because he thinks he screwed something up in the process. He’s also going to try printing with TPU, which we were just about to recommend for its flexibility.

There are many ways to cast metal on the (relatively) cheap. Have you considered Kinetic Sand?

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Building A Lego Paper Shredder

March 11, 2022 by Lewin Day 3 Comments

Sometimes we need to destroy documents before throwing them away for security reasons, and shredders are a primary way of achieving that. If you don’t have your own, you might consider building your own, like [Brick Experiment Channel] did using Lego.

First attempts at shredding a small slip of paper with interlocking gears were a failure, merely crumpling the paper in an attractive rippled manner. As the “Top Secret” piece of paper says, “If you can read this, the shredder didn’t work.” Adding more gears managed to gouge a couple holes in the paper, but it was still far from effective. Continuing down this path further only stalled the Lego motor.

A redesign with different sized gears did eventually manage to tear the paper into large chunks. One set of gears would hold on to the paper while a following set would tear away a section. A further modification combined this method with using bevel gears as a sort of blade, and improved shredding performance further, to the point where the paper was torn into satisfyingly tiny fragments.

It’s a fun little build, even if it won’t come close to taking on a full page of A4. It’s a great example of what can be achieved when you set a simple goal with readily measurable outcomes, in this case, the legibility of the original message on the paper.

We’ve seen a few shredders around here before too. Video after the break.
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Making A Locket From A Coin

March 11, 2022 by Lewin Day 9 Comments

Some countries have strict laws around the destruction or alteration of issued currency, but then again, some countries don’t. Citizens of those in the latter category may enjoy undertaking a build similar to this locket created by [Elier Olivos], crafted from a large coin.

A compass is first used to mark out a line on the coin’s perimeter, before it is cut in half with a fret saw. Once the two halves of the coin are smoothed out, it’s then time to heat them and quench them so they’re more malleable for pounding into a slightly domed shape. Metal rings are then fabricated and added to each half to give the locket some depth.

A hinge is then carefully made and fixed into the edges of the coin halves, giving the closed coin an almost seamless outside appearance. A small latch installed on the inside helps hold the locket closed. The final touches are to attach a loop for affixing the locket to a chain for the wearer, and to polish the inside of the locket up to a mirror shine.

[Elier] makes the build look easy through a combination of his amazing skills with his hands and the help of a some esoteric tooling. It can be very relaxing to take in a video of a master at work, and we’ve seen some great examples recently. Video after the break.

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You Can Build Your Own Sushi Train

March 11, 2022 by Lewin Day 20 Comments

According to [Garage Avenger], in Norwegian culture it’s considered impolite to ask for things to be passed across a dinner table, so much standing and reaching is the course of the day. To assist in reducing the effort required, he set about building his own sushi train device to solve the problem, giving equal condiment access to all!

The system is capable of taking plenty of weight from heavy dinner bowls, altogether quite different than relatively-light sushi dishes on plastic plates.

The system is actually relatively simple, relying on a Wemos D1 Mini controlled by a Blynk app to run the show. Mechanically, a large drive gears is turned by a stepper motor to drive the wooden conveyor chain that actually makes up the “sushi train.” The chain links ride on a bed of Norwegian one krone coins acting as rollers.

The result is a working table-sized sushi train that really does carry plates around well. It didn’t stop people leaning over [Garage Avenger] at the dinner table, but it makes a great centerpiece on the dinner table for sharing dishes like tacos.

We’ve seen similar table technology, the Lazy Susan, around these parts before. Video after the break.
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Very Fancy Nail Is Actually A Secret Jewlery Stash

March 10, 2022 by Lewin Day 10 Comments

Typically, nails are purpose-built things made to hold bits of wood together, with their entire design focused on that purpose. However, [W&M Levsha] went in much the other direction, crafting one very fancy expensive nail in what we can only explain as a masterful demonstration of their skills.

The build starts with a piece of brass tube, which is engraved with a delicate pattern on an automated lathe. After clean up, the spiralling lines are attractive on the polished brass.A plug is then made for the end of the tube, which gets filed into a point to resemble a nail, hiding the seam between the plug and the tube.

The tube is then threaded to accept a nail head that screws into the top, allowing the “nail” to act as a fancy little stash, which [W&M Levsha] shows off by placing a bracelet inside. The project is finished by crafting a stunning wooden box to hold the fancy nail.

We’ve seen [W&M Levsha]’s handywork before; the cap-gun cigarette lighter was a similarly impressive feat of machining and craftsmanship. Video after the break.

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