3D Printing A Water-Cooled Jet Engine?

May 30, 2022 by 14 Comments

Everybody knows the trick to holding a candle flame to a balloon without it bursting — that of adding a little water before the air to absorb the heat from the relatively cool flame. So [Integza], in his quest to 3D print a jet engine wondered if the same principle could applied to a 3D printed combustion chamber. First things first, the little puddle of water was replaced with a pumped flow, from an external reservoir, giving the thin plastic inner surface at least a vague chance of survival. Whilst this whole plan might seem pretty bonkers (although we admit, not so much if you’ve seen any of other videos in the channel lately) the idea has some merit. Liquid cooling the combustion jacket is used in a great many rocket engine designs, we note, the German WWII V2 rocket used this idea with great success, along with many others. After all, some materials will only soften and become structurally weak if they get hot enough in any spot, so if it is sufficiently conductive, then the excess heat can be removed from the outer surface and keep the surface temperature within sensible bounds. Since resin is a thermoset plastic, and will burn, rather than melt, this behaviour will be different, but not necessarily better for this application.

The combustion chamber itself didn’t burn

The issue we can see, is balancing the thermal conductivity of the resin wall, with the rate of cooling from the water flow, whilst making it thick enough to withstand the pressure of combustion, and any shock components. Quite a complicated task if you ask us. Is resin the right material for the job? Probably not, but it’s fun finding out anyway! In the end [Integza] managed to come up with a design, that with the help of a metal injector separator plate, survived long enough to maintain some sort of combustion, until the plate overheated and burned the resin around its support. Better luck next time!

This isn’t the first time attempting to use 3D printed resin for such an application, here’s an attempt to use the air-multiplier type setup with a combustion chamber. Of course making a combustion chamber from a toilet roll holder is far more sensible, just as [colinfurze] will attest, don’t try this at home folks!

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picture of finished mp3 player that uses a cartridge to select songs

An MP3 Player That Gives Off Nintendo Vibez

May 30, 2022 by 3 Comments

We’re definitely pretty fond of the DIY MP3 players here at Hackaday, but we don’t think we’ve seen one like CartridgeMP3 from [jpet26] before.

All the electrical components are what we’ve come to expect. [jpet26] uses the popular VS1053 decoder to read MP3 files stored on an SD card. He also includes a potentiometer for adjusting volume, a USB C port for power and programming, a headphone jack for the audio output, a general-purpose status LED, and an on/off switch.

But what really caught our attention is the form factor [jpet26] selected for his MP3 player. Though the MP3 files are stored on an SD card, he uses a cartridge interface, similar to that of a Nintendo 64 or Game Boy of yesteryear, to choose which MP3 to play from the SD card. The cartridge interface is tied to a few GPIO pins and by reading the status of each pin, the device determines which MP3 to select.

You could say that the cartridge is a little unnecessary, and we wouldn’t argue with you. The cartridge doesn’t actually store the MP3 files, the SD card does. It might make a bit more sense if the cartridge housed the SD card itself with a few select MP3s stored on the card. That would be a quirky way of sharing your favorite playlists with your friends. So, yeah some clumsy handshaking there, but who isn’t guilty of that from time to time? We like it and thought you might appreciate it as well.

Cool MP3 player, [jpet26]! May we suggest a speaker for V2? And maybe some flex cables.

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Practical Wireless “Tele-Tennis” Build After Only 34 Years

May 30, 2022 by 8 Comments
Home-etched PCBs ready for drilling

Back in November 1974 the publication “Practical Wireless” produced a five-part article series showing the reader how to construct a version of the popular “pong” game that could be played on the television screen available in the typical British home. [Grant Searle] had wanted to build this project for years, but it took him until 2008 to find the opportunity to do so. The magazine article printed PCB layouts to 1:1 scale, with a bill of materials and assembly instructions. After each month, the reader would have an assembled the project a little more, with the final month dedicated to point-to-point wiring and final setup. Subsequent months contained some enhancements such as a scoring system and sound effects, but these are not yet part of the main build. In order to understand the build, you will need to download the PDF copy of the magazines prints. (And if you’re an electronics nerd like this scribe, you’ve already done that right?)

A tidy assembly job with an authentic retro style

The electronics are based upon pure discrete 7400-series logic, 741 opamp-based ramp generators and, you guessed it, 555 timers. The way the various boards have discrete functions is particularly interesting. For example, in part 3, the PCB described (board A) not only is the master field/line sync generator, but also generates the video signals for the ball, with its position and size determined in an analogue fashion. Signals coming into the board from Board C (top/bottom base) cause a discrete flip-flop to toggle, changing the ball’s direction as it ‘bounces’ off the edge of the screen. Each board generates its own video signal, which are then all combined in the final video mixer (board E) that simply wire-OR’s them all with the composite sync to generate the composite video needed. This would have been tapped off and fed to a UHF video modulator, but [Grant] chose not to install that for the build. The whole thing was wrapped up inside an MDF case, coated in that dubious fake-wood plastic wrap, for that very 70’s aesthetic some of us remember fondly.

Pong is such a popular classic game, that we’ve covered many, many variants over the years. Here’s one that’s purely mechanical, another that uses the original PCB with a visually appealing twist, and finally, a completely virtual simulation of the original arcade circuit, courtesy of Falstad. We’re sure there will be many more to come.

Thanks [JohnU] for the tip!

A small round NRF51822 board glued to the underside of a mailbox lid, with a small vibration sensor attached

Check Your Mailbox Using The AirTag Infrastructure

May 30, 2022 by 32 Comments

When a company creates an infrastructure of devices, we sometimes subvert this infrastructure and use it to solve tricky problems. For example, here’s a question that many a hacker has pondered – how do you detect when someone puts mail into your mailbox? Depending on the availability of power and wireless/wired connectivity options, this problem can range from “very easy” to “impractical to solve”. [dakhnod] just made this problem trivial for the vast majority of hackers, with the FakeTag project – piggybacking off the Apple’s AirTag infrastructure.

This project uses a cheap generic CR2032-powered NRF51822 board, sending the mailbox status over the FindMy system Apple has built for the AirTag devices. For the incoming mail detection, he uses a simple vibration sensor, glued to the flap lid – we imagine that, for flap-less mailboxes, an optical sensor or a different kind of mechanical sensor could be used instead. Every time someone with a FindMy-friendly iPhone passes by [dakhnod]’s mailbox, he gets an update on its status, with a counter of times the sensor has been triggered. [dakhnod] estimates that the device could run for up to a year on a single battery.

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A frosted glass disk with geometrical markers

Using A Laser Cutter To Replicate An Optical Comparator Screen

May 30, 2022 by 13 Comments

Precision instruments often contain specialized components that are essential to their function, but nearly impossible to replace if they fail. [Andre] had just such a problem with an optical comparator, which is an instrument typically used in machine shops to help check the tolerances of a finished part. It does this by projecting a magnified picture of an object onto a glass screen with markings showing angles and distances.

In the old comparator [Andre] bought on eBay, the markings on the glass had faded to such a degree that the instrument was almost unusable. So he contacted [James] over at Clough42, who was able to create a near-perfect replacement screen by using a laser cutter, as shown in the video embedded below.

The first step was to replicate the screen’s markings in a CAD program. [James] explains the process in Fusion 360, demonstrating how you can generate all the different scales nearly automatically through the proper use of constraints, variables and patterns. He then transferred the drawing to Lightburn, which drives the laser cutter and etches the markings into a sheet of glass covered with CerMark, a marking solution that turns a deep black when heated by a laser.

After etching, the final step was to apply frosting to the glass to turn it into a projection screen. While there are several ways to achieve this, [James] went for a simple spray-based method that gave surprisingly good results. It took a few experiments to find out that etching the markings on the back of the glass and applying the frosting on that side as well gave the best combination of sharpness and durability.

[James]’s project shows that even delicate instruments with custom glass components can be repaired, if you just have the right tools. A similar strategy might also work for creating custom scales for analog meters, or even old radio dials. If you’re not familiar with laser cutters, have a look at our experiments with an Ortur model. Thanks for the tip, [poiuyt]!

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Laser-Engraving Hairlines: When A Line Isn’t A Line

May 29, 2022 by 8 Comments

When is a line not a line? When it’s a series of tiny dots, of course!

The line is actually tiny, laser-etched craters, 0.25 mm center-to-center.

That’s the technique [Ed Nisley] used to create a super-fine, colored hairline in a piece of clear plastic — all part of his project to re-create a classic Tektronix analog calculator from the 1960s, but more on that in a moment.

[Ed] tried a variety of methods and techniques, including laser engraving a solid line, and milling a line with an extremely tiny v-tool. Results were serviceable, but what really did the trick was a series of tiny laser-etched craters filled in with a red marker. That resulted in what appears — to the naked eye — as an extremely fine hairline. But when magnified, as shown here, one can see it is really a series of small craters. The color comes from coloring in the line with a red marker, then wiping the excess off with some alcohol. The remaining pigment sitting in the craters gives just the right amount of color.

This is all part of [Ed]’s efforts to re-create the Tektronix Circuit Computer, a circular slide rule capable of calculating all kinds of useful electrical engineering-related things. And if you find yourself looking to design and build your own circular slide rule from scratch? We have you covered.

Autonomous Inflatable Canoe

May 29, 2022 by 6 Comments

With the summer months nearly upon us, many are dreaming of warm afternoons spent floating on a quiet lake. Unless you’re [Kolins] anyway. Apparently his idea of a good time is controlling a full-sized inflatable canoe not from onboard with a pair of oars, but from the shore with a RC transmitter.

The linkage design allows the motor to be adjusted vertically.

Of course, as the video after the break shows, just because the canoe is powered by a remotely operated electric trolling motor doesn’t mean it can’t still carry human occupants. In fact, with the addition of a Matek F405-Wing flight controller running the rover variant of ArduPilot, the boat can even take you on a little tour of the lake while you kick back and relax.

We like that this project took the path of least resistance wherever possible. Rather than trying to spin up his own custom propulsion unit, and inevitably dealing with the challenge of waterproofing it, [Kolins] built his system around a commercial trolling motor. A clever servo mechanism physically turns the motor in much the same way a human operator would, while the speed is controlled with a suitably beefy ESC from Traxxas placed between the motor and its lead-acid battery.

It doesn’t look like there’s been any permanent mechanical or electrical changes made to the motor, which makes the whole thing a lot easier to replicate. We’ve talked in the past about the relative rarity of low-cost robotic watercraft, so a “bolt-on” propulsion module like this that can turn a cheap inflatable boat into an autonomous platform for research and experimentation is very interesting.

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