Building a Battery from Molten Salt

During World War II a scientist named Georg Otto Erb developed the molten salt battery for use in military applications. The war ended before Erb’s batteries found any real use, but British Intelligence wrote a report about the technology and the United States adopted the technology for artillery fuses.

Molten salt batteries have two main advantages. First, you can store them for a long time (50 years or more) with no problems. Once the salt melts (usually from a pyrotechnic charge), the battery can produce a lot of energy for a relatively short period of time thanks to the high ionic conductivity of the electrolyte (about three times that of sulfuric acid).

[OrbitalDesigns] couldn’t find a DIY version of a molten salt battery so he decided to make one himself. Although he didn’t get the amount of power you’d find in a commercial design, it did provide 1.6V and enough power to light an LED.

The electrolyte was a mixture of potassium chloride and lithium chloride and melts at about 350 to 400 degrees Celsius. He used nickel and magnesium for electrodes. Potassium chloride is used as a salt substitute, so it isn’t dangerous to handle (at least, no more dangerous than anything else heated to 400 degrees Celsius). The lithium compound, however, is slightly toxic (even though it was briefly sold as a salt substitute, also). If you try to replicate the battery, be sure you read the MSDS for all the materials.

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RIP: HitchBot

Equal parts art project and social media experiment, with a dash of backyard hackery “robotics” thrown in for good measure, hitchBot was an experiment in the kindness of strangers. That is, the kindness of strangers toward a beer bucket filled with a bunch of electronics with a cute LED smiley face.

The experiment came to a tragic end (vandalism, naturally) in Philadelphia PA, after travelling a month across Canada, ten days in Germany, and yet another month across the Netherlands. It survived two weeks in the USA, which is more than the cynics would have guessed, but a few Grand Canyons short of the American Dream.

Professors [David Smith] and [Frauke Zeller] built hitchBot to see how far cuteness and social media buzz could go. [Smith], a former hitchhiker himself, also wanted hitchBot to be a commentary on how society’s attitudes toward hitching and public trust have changed since the 70s. Would people would pick it up on the side of the street, plug it in to their own cigarette lighters, and maybe even take it to a baseball game? Judging by hitchBot’s Twitter feed, the answer was yes. And for that, little bucket, we salute you!

But this is Hackaday, and we don’t pull punches, even for the recently deceased. It’s not clear how much “bot” there was in hitchBot. It looks like it had a GPS, batteries, and a solar cell. We can’t tell if it took its own pictures, but the photos on Twitter seem to be from another perspective. It had enough brains inside to read out Wikipedia entries and do some rudimentary voice recognition tasks, so it was a step up from Tweenbots but was still reassuringly non-Terminator.

Instead, hitchBot had more digital marketing mavens and social media savants on its payroll than [Miley Cyrus] and got tons of press coverage, which seems to have been part of the point from the very start. And by writing this blog post, we’re playing right into [Smith] and [Zeller]’s plan. If you make a robot / art project cute enough to win the hearts of many, they might just rebuild it. [Margaret Atwood] has even suggested on Twitter that people might crowdfund-up a hitchBot 2.0.

Our suggestion? Open-source the build plans, and let thousands of hitchBots take its place.

How to Rescue Your Quadcopter from a Tree

Whether it’s a new rocket, your latest quadcopter, or [Charlie Brown]’s kite, it always seems like there’s a tree waiting to catch and eat airborne projects. Sometimes you get lucky and find a way to climb up the tree to retrieve your wayward build, but most times you’re reduced to looking for rocks or sticks to fling up there in an attempt to shake it loose. But if you want to improve your chances of getting your stuff back, [U.S. Water Rockets] has a build for a retrieval tool made mostly from scrap bin parts that will help.

All you need is some PVC tubing, an old fishing reel and line, some latex surgical tubing, and a few dowels for projectiles. You can tell everything about the build from the BOM and stills, but the video after the break gives detailed instructions and shows it in action. Adding some fins to the dart or even substituting a cheap arrow from the sporting goods department of your favorite retailer might help with your aim. Even without fletching, the accuracy of the launcher is pretty good, and the range isn’t half bad either. Once the fishing line is over the branch that ate your quad it can be used to haul up successively stouter ropes, and pretty soon you’ll be shaking the tree like a boss.

Even if getting stuff out of trees isn’t on your immediate to-do list, this little hack could be put to other uses. Hams will use it to loft antennas up into trees, and tag-line placement for tree removal could be simplified with this tool. But if you still find yourself needing to retrieve stuff, you might want to be proactive and make your aerial robot tree-proof. That still won’t eliminate the need for drone-on-drone rooftop rescues.

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Shinewave Gamecube Controller Reacts to Smash Brothers

[Garrett Greenwood] plays Smash Brothers, and apparently quite seriously. So seriously that he needed to modify his controller with five Neopixels so that it flashed different color animations according to the combo he’s playing on the controller; tailored to match the colors of the moves of his favorite character, naturally.

All of this happens with an ATtiny85 as the brains, which we find quite ambitious. Indeed, [Garrett] started out thinking he could simply read each of the inputs from the controller directly into the microcontroller at the heart of the whole thing, but then counted up how many wires that would be, and looked at how many pins he had free (six), and thought up a better solution.

[Garrett]’s routine instead reads the single line that the Gamecube controller uses to send back to the console. The protocol is well understood, using long-short and short-long signals to encode bits. The only trick is that each bit is sent in four microseconds, so the decoding routine has to be fairly speedy. To make it work he had to do quite a bit of work. More about that, and the demo video, after the break.

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Homemade High Voltage Caps

Do you happen to have any 15,000 volt capacitors sitting around? [Ludic Science] didn’t so he did the next best thing. He built some.

If you understand the physics behind a capacitor (two parallel conductors separated by a dielectric) you won’t find the build process very surprising. [Ludic] uses transparency film as an insulator and aluminum foil for the conductive plates. Then he wraps them into a tube. He did throw in a few interesting tips about keeping the sheets smooth and how to attach the wires to the foil. The brown paper wrapper reminded us of old caps you might find in an antique radio.

The best part by far, though, was the demonstration of drawing an arc from a high voltage power supply with and without the capacitor in the circuit. As you might expect, playing with a few thousand volts charged into a capacitor requires a certain amount of caution, so be careful!

[Ludic] measured the capacitance value with a standard meter, but it wasn’t clear where the 15,000 volt rating came from. Maybe it was the power supply he used in the video and the capacitor could actually go higher.

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I am a Battery: Harvesting Heat Energy

If you get tired of charging batteries, you might be interested in [Hackarobot’s] energy harvesting demo. He uses a peltier device (although he’s really using it as a thermocouple which it is). A 1 farad super capacitor stores energy and an LTC3108 ultra low voltage converter with a 1:100 ratio transformer handles the conversion to a useful voltage.

The truth is, the amount of energy harvested is probably pretty small–he didn’t really characterize it other than to light an LED. In addition, we wondered if a proper thermocouple would work better (some old Russian radios used thermocouples either in fireplaces or kerosene lamps to avoid requiring batteries). Although a Peltier device and a thermocouple both use the Seebeck effect, they are optimized for different purposes. Thermocouples generate voltage from a temperature differential and Peltier modules generate temperature differentials from voltage.

However, as [Hackarobot] points out, the same technique might be useful with other alternate power sources like solar cells or other small generators. The module used has selectable output voltages ranging from 2.35V to 5V.

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Everything You Wanted to Know About Oscillators

Ever wonder how a crystal oscillator works? How does that little metal can with a sliver of quartz start vibrating to produce a clock signal for just about everything we use, while doing it in the accuracy range in the parts per million and cost practically nothing?

Well [Craig] decided its about time for an in depth tutorial  that covers everything you need to know to understand, design, and construct your very own. Wrapped up in a 41 minute video, [Craig]  covers the absolute basic theories and designs, math, datasheet explanation of crystals, and even a practical example of a Pierce crystal oscillator, suitable for use in a HF transceiver. Now you can make your own for your own application no matter if you’re just trying to save a pin on your favorite micro, or making a radio transceiver.

With this wealth of knowledge, whether you are learning for the first time, or just need a refresher, you should join us after the break, kick back and check out this highly informative video.

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