3D Printed Server Case Holds 14 Raspberry Pis

If you ever need to cluster up to 14 Raspberry Pis and an equal number of 2.5 inch hard drives, you might want to look at the Raspberry Pi Server Mark III case from [Ivan Kuleshov]. The original Mark I design came from Thingiverse, but the Mark III is a complete redesign.

The redesign allows for more boards along with a reduction in the number of parts. That takes less plastic and less time to print. The design is also modular, so there should be new components in the future.

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Analyzing The “Source Code” Of The COVID-19 Vaccine

Computer programs are written in code, which comes in many forms. At the lowest level, there’s machine code and assembly, while higher-level languages like C and Python aim to be more human-readable. However, the natural world has source code too, in the form of DNA and RNA strings that contain the code for the building blocks of life. [Bert] decided to take a look at the mRNA source code of Tozinameran, the COVID-19 vaccine developed by BioNTech and Pfizer.

The analysis is simple enough for the general reader, while nonetheless explaining some highly complex concepts at the cutting edge of biology. From codon substitutions for efficiency and the Ψ-base substitution to avoid the vaccine being destroyed by the immune system, to the complex initialisation string required at the start of the RNA sequence, [Bert] clearly explains the clever coding hacks that made the vaccine possible. Particularly interesting to note is the Prolase substitution, a technique developed in 2017. This allows the production of coronavirus spike proteins in isolation of the whole virus, in order to safely prime the immune system.

It’s a great primer and we can imagine it might inspire some to delve further into the rich world of genetics and biology. We’ve featured other cutting edge stories on COVID-19 too; [Dan Maloney] took a look at how CRISPR techniques are helping with the testing effort. If there’s one thing the 2020 pandemic has shown, it’s humanity’s ability to rapidly develop new technology in the face of a crisis.

Squeezing Every Bit From An ATMega

While the ATMega328 is “mega” for a microcontroller, it’s still a fairly limited platform. It has plenty of I/O and working memory for most tasks, but this Battleship game that [thorlancaster328] has put together really stretches the capabilities of this tiny chip. Normally a Battleship game wouldn’t be that complicated, but this one has audio, an LED display, and can also play a fine rendition of Nyan Cat to boot, which really puts the Atmel chip through its paces.

The audio is played through a 512-byte buffer and an interrupt triggers the microcontroller when to fill the buffer while it works on the other processes. The 12×12 LED display is also fed through a shift register triggered by the same interrupt as the audio, and since the build uses so many shift registers the microcontroller can actually output four separate displays (two players, each with a dispaly for shots and one for ships). It will also eventually support a player-vs-computer mode for the battleship game, and also has a mode where it plays Nyan cat just to demonstrate its own capabilities.

We’re pretty impressed with the amount of work this small microcontroller is doing, largely thanks to code optimization from its creator [thorlancaster328]. If there’s enough interest he also says he will provide the source code too. Until then, be sure to check out this other way of pushing a small microcontroller to its limits.

Thanks to [Thinkerer] for the tip!

Fox Hunting With Software-Defined Radio

Fox hunting, or direction finding, is a favorite pastime in the ham radio community where radio operators attempt to triangulate the position of a radio transmission. While it may have required a large amount of expensive equipment in the past, like most ham radio operations the advent of software-defined radio (SDR) has helped revolutionize this aspect of the hobby as well. [Aaron] shows us how to make use of SDR for direction finding using his custom SDR-based Linux distribution called DragonOS.

We have mentioned DragonOS before, but every iteration seems to add new features. This time it includes implementation of a software package called DF-Aggregator. The software (from [ckoval7]), along with the rest of DragonOS, is loaded onto a set of (typically at least three) networked Raspberry Pis. The networked computers can communicate information about the radio waves they receive, and make direction finding another capable feature found in this distribution.

[Aaron] has a few videos showing the process of setting this up and using it, and all of the software is available for attempting something like this on your own. While the future of ham radio as a hobby does remain in doubt, projects like this which bring classic ham activities to the SDR realm really go a long way to reviving it.

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Indoor Antennas Worthy Of 007

Many ham radio operators now live where installing an outdoor antenna is all but impossible. It seems that homeowner’s associations are on the lookout for the non-conformity of the dreaded ham radio antenna. [Peter] can sympathize, and has a solution based on lessons of spycraft from the cold war.

[Peter] points out that spies like the [Krogers] needed to report British Navy secrets like the plans for a nuclear boomer sub to Russia but didn’t want to attract the attention of their neighbors. In this case, the transmitter itself was so well-hidden that it took MI5 nine days to find the first of them. Clearly, then, there wasn’t a giant antenna on the roof. If there had been, the authorities could simply follow the feedline to find the radio. A concealed spy antenna might be just the ticket for a deed-restricted ham radio station.

The antenna the [Kroger’s] used was a 22-meter wire in the attic of their home. Keep in mind, the old tube transmitters were less finicky about SWR and by adjusting the loading circuits, you could transmit into almost anything. Paradoxically, older houses work better with indoor antennas because they lack things like solar cell panels, radiant barriers, and metallic insulation.

Like many people, [Peter] likes loop antennas for indoor use. He also shows other types of indoor antennas. They probably won’t do as much good as a proper outdoor antenna, but you can make quite a few contacts with some skill, some luck, and good propagation. [Peter] has some period spy radios, which are always interesting to see. By today’s standards, they aren’t especially small, but for their day they are positively tiny. Video after the break.

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Legged Robots Put On Wheels And Skate Away

We don’t know how much time passed between the invention of the wheel and someone putting wheels on their feet, but we expect that was a great moment of discovery: combining the ability to roll off at speed and our leg’s ability to quickly adapt to changing terrain. Now that we have a wide assortment of recreational wheeled footwear, what’s next? How about teaching robots to skate, too? An IEEE Spectrum interview with [Marko Bjelonic] of ETH Zürich describes progress by one of many research teams working on the problem.

For many of us, the first robot we saw rolling on powered wheels at the end of actively articulated legs was when footage of the Boston Dynamics ‘Handle’ project surfaced a few years ago. Rolling up and down a wide variety of terrain and performing an occasional jump, its athleticism caused quite a stir in robotics circles. But when Handle was introduced as a commercial product, its job was… stacking boxes in a warehouse? That was disappointing. Warehouse floors are quite flat, leaving Handle’s agility under-utilized.

Boston Dynamic has typically been pretty tight-lipped on details of their robotics development, so we may never know the full story behind Handle. But what they have definitely accomplished is getting a lot more people thinking about the control problems involved. Even for humans, we face a nontrivial learning curve paved with bruised and occasionally broken body parts, and that’s even before we start applying power to the wheels. So there are plenty of problems to solve, generating a steady stream of research papers describing how robots might master this mode of locomotion.

Adding to the excitement is the fact this is becoming an area where reality is catching up to fiction, as wheeled-legged robots have been imagined in forms like Tachikoma of Ghost in the Shell. While those fictional robots have inspired projects ranging from LEGO creations to 28-servo beasts, their wheel and leg motions have not been autonomously coordinated as they are in this generation of research robots.

As control algorithms mature in robot research labs around the world, we’re confident we’ll see wheeled-legged robots finding applications in other fields. This concept is far too cool to be left stacking boxes in a warehouse.

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Casting Skateboard Wheels With A 3D Printed Mold

We’ll admit that most of the Hackaday staff wouldn’t get too far on a skateboard, but that doesn’t mean we can’t appreciate the impressive DIY wheels that [Chris McCann] has managed to cast using 3D printed molds. From unique color combinations to experimental materials, the process certainly opens up some interesting possibilities for those looking to truly customize their rides. Though it’s worth noting there’s a certain element of risk involved; should a set of homemade wheels fail at speed, it could go rather poorly for the rider.

Both the STL and STEP files for the mold have been released under the Creative Commons Attribution 4.0 license, meaning anyone with a 3D printer can follow along at home. Unfortunately, it’s not quite as simple as clicking print and coming back to a usable mold. Because of the layer lines inherent to FDM 3D printing, the inside of the mold needs to be thoroughly sanded and polished. [Chris] mentions that printing the mold in ABS and using vapor smoothing might be a workable alternative to elbow grease and PLA, but he hasn’t personally tried it yet.

Once you’ve got the three part mold printed, smoothed, and coated with an appropriate release agent like petroleum jelly, it’s time to make some wheels. The core of each wheel is actually 3D printed from PETG, which should give it pretty reasonable impact resistance. If you have access to a lathe, producing aluminum cores shouldn’t be too difficult either. With the core loaded into the mold, urethane resin is poured in through the top until all the empty space is filled.

But you’re not done yet. All those little air bubbles in the resin need to be dealt with before it cures. [Chris] puts his filled molds into a pressure chamber, though he mentions that vacuum degassing might also be a possibility depending on the urethane mixture used. After everything is solidified, the mold can easily be taken apart to reveal the newly cast wheel.

While there’s often some trial and error involved, 3D printing and resin casting are an undeniably powerful combination. If you can master the techniques involved, you can produce some very impressive parts that otherwise would be exceptionally difficult to produce on a hacker’s budget. Especially when you’re ready to start casting molten metal.

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