Hybrid Rocket Engine Combines Ceramic Aerospike With 3D Printed Fuel

May 13, 2021 by 23 Comments

[Integza] has worked hard over the last year, crafting a variety of types of rocket and jet engine, primarily using 3D printed parts. Due to the weaknesses of plastic, all of which conflict with the general material requirements for an engine that gets hot, he has had less thrust and more meltdowns than he would have liked. Undeterred, he presses on, now with a hybrid rocket aerospike design. The goal? Actually generating some thrust for once!

The latest project makes the most of what [Integza] has learned. The aerospike nozzle is 3D printed, but out of a special thick ceramic-loaded resin, using a Bison 1000 DLP printer. This allowed [Integza] to print thicker ceramic parts which shrunk less when placed in a kiln, thus negating the cracking experienced with his earlier work. The new nozzle is paired with a steel rocket casing to help contain combustion gases, and the rocket fuel is 3D printed ASA plastic. 3D printing the fuel is particularly cool, as it allows for easy experimentation with grain shape to tune thrust profiles.

With the oxygen pumping, the new design produces some thrust, though [Integza] is yet to instrument the test platform to actually measure results. While the nozzles are still failing over a short period of time, the test burns were far less explosive – and far more propulsive – than his previous efforts. We look forward to further development, and hope [Integza’s] designs one day soar high into the sky. Video after the break.

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Piggy Bank Slot Machine Puts A Spin On Saving

May 12, 2021 by 7 Comments

Saving money is inherently no fun until the time comes that you get to spend it on something awesome. Wouldn’t you be more likely to drop your coins into a piggy bank if there was a chance for an immediate payout that might exceed the amount you put in? We know we would. And the best part is, if you put such a piggy bank slot machine out in the open where your friends and neighbors can play with it, you’ll probably make even more money. As they say, the house always wins.

Drop a coin in the slot and it passes through a pair of wires that act as a simple switch to start the reels spinning. Inside is an Arduino Uno and a giant printed screw feeder that’s driven by a small stepper motor and a pair of printed gears. The reels have been modernized and the display is made of four individual LED matrices that appear as a single unit thanks to some smoky adhesive film.

This beautiful little machine took a solid week of 3D printing, which includes 32 hours wasted on a huge piece that failed twice. [Max 3D Design] tried rotating the model 180° in the slicer and thankfully, that solved the problem. Then it was on to countless hours of sanding, smoothing with body filler, priming, and painting to make it look fantastic.

If you want to make your own, all the files are up on Thingiverse. The code isn’t shown, but we know for a fact that Arduino slot machine code is out there already. Check out the build and demo video after the break.

As much as we like this build’s simplicity, it would be more slot machine-like if there was a handle to pull. Turns out you can print those, too.

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Apple AirTag Spills Its Secrets

May 10, 2021 by 17 Comments

The Apple AirTag is a $29 Bluetooth beacon that sticks onto your stuff and helps you locate it when lost. It’s more than just a beeper though, the idea is that it can be silently spotted by any iDevice — almost like a crowd-sourced mesh network — and its owner alerted of its position wherever they are in the world.

There are so many questions about its privacy implications despite Apple’s reassurances, so naturally it has been of great interest to those who research such things. First among those working on it to gain control of its nRF52832 microcontroller is [Stacksmashing], who used a glitching technique whereby the chip’s internal power supply is interrupted with precise timing, to bypass the internally enabled protection of its debug port. The firmware has been dumped, and of course a tag has been repurposed for the far more worthwhile application of Rickrolling Bluetooth snoopers.

The idea of a global network of every iDevice helping reunite owners with their lost possessions is on the face of it a very interesting one, and Apple are at great pains on the AirTag product page to reassure customers about the system’s security. On one hand this work opens up the AirTag as a slightly expensive way to get an nRF microcontroller for other applications, but the real value will come as the firmware is analysed to see how at the tag itself works.

[Stacksmashing] has appeared on these pages many times before, often in the context of Nintendo hardware. Just one piece of work is the guide to opening up a Nintendo Game and Watch.

Hackaday Podcast 113: Python Switching To Match, A Magnetic Dyno, A Flying Dino, And A Spinning Sequencer

April 9, 2021 by 2 Comments

Hackaday editors Mike Szczys and Elliot Williams recap a week of great hacks. You won’t want to miss the dynamometer Leo Fernekes built to measure the power output of his Sterling engine, which is also DIY. In this age of lithium-powered multirotors, it’s nice to step back and appreciate a hand-built rubberband-powered ornithopter.

We have a surprising amount to say about Python’s addition of the match statement (not be be confused with switch statements). And when it comes to electromechanical synth gear, it’s hard to beat a spinning tape-head sequencer.

Take a look at the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!

Direct download (~60 MB)

Places to follow Hackaday podcasts:

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Raspberry Pi Spigot Puts Digits Of Pi On Tap

April 6, 2021 by 11 Comments

What did you do for Pi Day? Play with your Raspberry Pi 400? Eat some pizza or other typically round objects and recite all nine digits you’ve got memorized? That’s about where we were at this year. But not [bornach], no. [bornach] went all out and built a spigot that spews digits of Pi well past the first nine decimal places.

This clever spigot sculpture implements the spigot algorithm for generating digits of Pi one-by-one in a stream on to a chain of 8×8 matrices, and does so using a Raspberry Pi (of course). The point of the spigot algorithm is to store as few numbers as possible at any given time by reusing variables. We love the way the digits materialize on the matrix, almost as if they are ink being activated by water. Be sure to check out the build and demo video after the break.

That 10k pot on the top really does control the spigot — since the Pi has no ADC, [bornach] is using the potentiometer to charge a capacitor and using the time it takes to reach the threshold to decide whether the faucet is open or closed. There are a couple of hacks at play here, including the Popsicle-stick LED matrix bracing and the HAT [bornach] fashioned so the daisy-chained 8×8 LED modules could interface with the Pi.

We love Raspberry Pis of all eras around here, especially the darling new Pico. Diminutive as it may be, the Pico can be sliced even smaller with a hacksaw if you don’t mind losing a few GPIO pins.

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Flight Of The Pterothopter: A Jurassic-Inspired Ornithopter

April 6, 2021 by 14 Comments

Ornithopters look silly. They look like something that shouldn’t work. An airplane with no propeller and wings that go flappy-flappy? No way that thing is going to fly. There are, however, a multitude of hobbyists, researchers, and birds who would heartily disagree with that sentiment, because ornithopters do fly. And they are almost mesmerizing to watch when they do it, which is just one reason we love [Hobi Cerdas]’s build of the Pterothopter, a rubber band-powered ornithopter modeled after a pterodactyl.

All joking aside, the science and research behind ornithopters and, relatedly, how living organisms fly is fascinating in itself — which is why [Lewin Day] wrote that article about how bees manage to become airborne. We can lose hours reading about this stuff and watching videos of prototypes. While most models we can currently build are not as efficient as their propeller-powered counterparts, the potential of evolutionarily-perfected flying mechanisms is endlessly intriguing. That alone is enough to fuel builds like this for years to come.

As you can see in the video below, [Hobi Cerdas] went through his own research and development process as he got his Pterothopter to soar. The model proved too nose-heavy in its maiden flight, but that’s nothing a little raising of the tail section and a quick field decapitation couldn’t resolve. After a more successful second flight, he swapped in a thinner rubber band and modified the wing’s leading edge for more thrust. This allowed the tiny balsa dinosaur to really take off, flying long enough to have some very close encounters with buildings and trees.

For those of you already itching to build your own Pterothopter, the plans come from the Summer 2017 issue of Flapping Wings, the official newsletter of the Ornithopter Society (an organization we’re so happy to learn about today). You can also find more in-depth ornithopter build logs to help you get started. And, honestly, there’s no reason to limit yourself to uncontrolled flight; we’ve come across some very impressive RC ornithopters in the past.

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Spinning Up A Water Cooled 3D Printed Stirling Engine

March 31, 2021 by 7 Comments

The Stirling external combustion engine has fascinated gear heads since its inception, and while the technology has never enjoyed widespread commercialization, there’s a vibrant community of tinkerers who build and test their own takes on the idea. [Leo Fernekes] has been working on a small Stirling engine made from 3D printed parts and common hardware components, and in his latest video he walks viewers through the design and testing process.

We’ve seen Stirling engines with 3D printed parts before, but in most cases, they are just structural components. This time, [Leo] really wanted to push what could be done with plastic parts, so everything from the water jacket for the cold side of the cylinder to the gears and connecting rods of the rhombic drive has been printed. Beyond the bearings and rods, the most notable non-printed component is the stainless steel spice shaker that’s being used as the cylinder.

The piston is made of constrained steel wool.

Mating the hot metal cylinder to the 3D printed parts naturally introduced some problems. The solution [Leo] came up with was to design a toothed collar to hold the cylinder, which reduces the surface area that’s in direct contact. He then used a piece of empty SMD component feed tape as a insulator between the two components, and covered the whole joint in high-temperature silicone.

Like many homebrew Stirling engines, this one isn’t perfect. It vibrates too much, some of the internal components have a tendency to melt during extended runs, and in general, it needs some fine tuning. But it runs, and in the end, that’s really the most important thing with a project like this. Improvements will come with time, especially once [Leo] finishes building the dynamometer he hopes will give him some solid data on how the engine’s overall performance is impacted as he makes changes.

If you’ve got a glass test tube laying around, putting together a basic Stirling engine demonstration is probably a lot easier than you might think. Commercial kits are also available if you’re looking for something more substantial, but even those can benefit from some aftermarket modifications. With a little effort, you’ll have a power plant ready for the surface of Mars in no time.

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