When 3D Printing Gears, It Pays To Use The Right Resin

There are plenty of resins advertised as being suitable for functional applications and parts, but which is best and for what purpose?

According to [Jan Mrázek], if one is printing gears, then they are definitely not all the same. He recently got fantastic results with Siraya Tech Fast Mecha, a composite resin that contains a filler to improve its properties, and he has plenty of pictures and data to share.

[Jan] has identified some key features that are important for functional parts like gears. Dimensional accuracy is important, there should be low surface friction on mating surfaces, and the printed objects should be durable. Of course, nothing beats a good real-world test. [Jan] puts the resin to work with his favorite method: printing out a 1:85 compound planetary gearbox, and testing it to failure.

The results? The composite resin performed admirably, and somewhat to his surprise, the teeth on the little gears showed no signs of wear. We recommend checking out the results on his page. [Jan] has used the same process to test many different materials, and it’s always updated with all tests he has done to date.

Whether it’s working out all that can go wrong, or making flexible build plates before they were cool, We really admire [Jan Mrázek]’s commitment to getting the most out of 3D printing with resin.

Testing An Inexpensive CNC Spindle

The old saying “you get what you pay for” is a cautionary cliché, but is directly contrary to several other common sayings. In the case of [Spikee]’s planned CNC machine build, he took the more adventurous idiom of “no risk, no reward” to heart when he purchased these spindles for the machine from AliExpress. While the delivered product seemed fine, there were some problems that needed investigations.

Upon delivery of the spindle, everything seemed to work correctly out-of-the-box. Even the variable frequency drive, which was programmed at the factory, was working properly. But at around 8000 rpm the machine would begin shaking. The suspected part causing the vibration was the tool holder, so after checking the machine’s runout and also using a specialized vibration sensor this was confirmed to be the case.

Luckily [Spikee] was able to get a refund on the tool holders since they were out of spec, but still has a quite capable spindle on his hands for an excellent price. Without some skills in troubleshooting he might have returned the entire machine unnecessarily. If you are looking for some other ideas in setting up an inexpensive CNC machine, you might also like to look at BLDC motors from a remote control vehicle.

The Big List Of Naughty Strings Helps Find Those User Input Problems

Any software that accepts user input must take some effort to sanitize incoming data, lest unexpected and unwelcome things happen. Here to make that easier is the Big List of Naughty Strings, an evolving list of edge cases, unusual characters, script-injection fragments, and all-around nonstandard stuff aimed at QA testers, developers, and the curious. It’s a big list that has grown over the years, and every piece of it is still (technically) just a string.

These strings have a high probability of surfacing any problems with handling user input. They won’t necessarily break anything, but they may cause unexpected things to happen and help point out any issues that need fixing. After all, many attacks hinge on being able to send unexpected inputs that don’t get properly sanitized.

Finding bad inputs is not always entirely straightforward, but at least the Big List of Naughty Strings is available in a variety of formats to make it easy to use. [Max Woolf] has been maintaining the list for years, but if you haven’t heard of it yet and think it might come in useful, now’s the time to give it a look. Now you can help ensure your system can handle things like someone registering a company named ; DROP TABLE “COMPANIES”;– LTD.

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Hackaday Links: June 12, 2022

“Don’t worry, that’ll buff right out.” Alarming news this week as the James Webb Space Telescope team announced that a meteoroid had hit the space observatory’s massive primary mirror. While far from unexpected, the strike on mirror segment C3 (the sixth mirror from the top going clockwise, roughly in the “south southeast” position) that occurred back in late May was larger than any of the simulations or test strikes performed on Earth prior to launch. It was also not part of any known meteoroid storm in the telescope’s orbit; if it had been, controllers would have been able to maneuver the spacecraft to protect the gold-plated beryllium segments. The rogue space rock apparently did enough damage to be noticeable in the data coming back from the telescope and to require adjustment to the position of the mirror segment. While it certainly won’t be the last time this happens, it would have been nice to see one picture from Webb before it started accumulating hits.

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Theory, Practice, And Ducted Fans

About a year ago, [Wyman’s Workshop] needed a fan. But not just a regular-old fan, no sir. A ducted fan. You know, those fancy fan designs where the stationary shroud is so close to the moving fan blades that there’s essentially no gap, and a huge gain in aerodynamic efficiency? At least in theory?

Well, in practice, you can watch how it turned out in this video. (Also embedded below.) If you’re more of a “how-to-build-it” type, you’ll want to check out his build video — there’s lots of gluing 3D prints and woodworking. But we’re just in it for the ducted fan data!

And that’s why we’re writing it up! [Wyman] made a nice thrust-testing rig that the fan can pull on to figure out how much force it put out. And the theory aimed at 652 g of thrust, which was roughly confirmed. And then you get to power: with a 500 watt motor, he ended up producing 47 watts. Spoiler: he’s overloading the motor, even though he used a fairly beefy bench grinder motor.

So he re-did the fan design, from scratch, to better match the motor. And it performed better than the theory said it would. A pleasant surprise, but it meant re-doing the theory, including the full volume of the fan blade, which finally brought theory and practice together. Which then lead him design a whole slew of fan blades and test them out against each other.

He ends the video with a teaser that he’ll show us the results from various inlet profiles and fan cones and such. But the video is a year old, so we’re not holding our breath. Still, if you’re at all interested in fan design, and aren’t afraid of high-school physics, it’s worth your time.

Don’t care about the advantages of ducted fans, but simply want to make your quad look totally awesome?  Have we got the hack for you!

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Stress-Testing An Arduino’s EEPROM

Every time one of us flashes an Arduino’s internal memory, a nagging thought in the backs of our minds reminds us that, although everything in life is impermanent, nonvolatile re-writable memory is even more temporary. With a fixed number of writes until any EEPROM module fails, are we wasting writes every time we upload code with a mistake? The short answer is that most of us shouldn’t really be concerned with this unless we do what [AnotherMaker] has done and continually write data until the memory in an Arduino finally fails.

The software for this is fairly simple. He simply writes the first 256 ints with all zeros, reads them to make sure they are all there, and then repeats the process with ones. After iterating this for literally millions of times continuously over the course of about a month he was finally able to get his first read failure. Further writes past this point only accelerated the demise of the memory module. With this method he was able to get nearly three million writes before the device failed, which is far beyond the tens or hundreds of thousands typically estimated for a device of this type.

To prove this wasn’t an outlier, [AnotherMaker] repeated the test, and did a few others while writing to a much smaller amount of memory. With this he was able to push the number of cycles to over five million. Assuming the Arduino Nano clone isn’t using an amazingly high-quality EEPROM we can safely assume that most of us have nothing to worry about and our Arduinos will be functional for decades to come. Unless a bad Windows driver accidentally bricks your device.

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Backpack COVID-19 lab

HDD Centrifuge Puts COVID-19 Testing Lab In A Backpack

Throughout this two-year global COVID-19 nightmare, one thing that has been sorely lacking is access to testing. “Flu-like symptoms” covers a lot of ground, and knowing if a sore throat is just a sore throat or something more is important enough that we’ve collectively plowed billions into testing. Unfortunately, the testing infrastructure remains unevenly distributed, which is a problem this backpack SARS-CoV-2 testing lab aims to address.

The portable lab, developed by [E. Emily Lin] and colleagues at the Queen Mary University of London, uses a technique called LAMP, for loop-mediated isothermal amplification. LAMP probably deserves an article of its own to explain the process, but suffice it to say that like PCR, LAMP amplifies nucleic acid sequences, but does so without the need for expensive thermal cycling equipment. The kit contains a microcentrifuge that’s fashioned from an e-waste hard drive, a 3D printed rotor, and an Arduino to drive the motor and control the speed. The centrifuge is designed to run on any 12 VDC source, meaning the lab can be powered by a car battery or solar panel if necessary. Readout relies on the trusty Mark I eyeball and a pH-indicating buffer that changes color depending on how much SARS-CoV-2 virus was in the sample.

Granted, the method used here still requires more skill to perform than a simple “spit on a stick” rapid antigen test, and it’s somewhat more subjective than the “gold standard” quantitative polymerase chain reaction (qPCR) assay. But the method is easily learned, and the kit’s portability, simple design, and low-cost construction could make it an important tool in attacking this pandemic, or the next one.

Thanks to [Christian Himmler] for the tip.