Explosions That Save Lives

January 6, 2017 by Dan Maloney 36 Comments

Normally, when something explodes it tends to be a bad day for all involved. But not every explosion is intended to maim or kill. Plenty of explosions are designed to save lives every day, from the highway to the cockpit to the power grid. Let’s look at some of these pyrotechnic wonders and how they keep us safe.

Explosive Bolts

The first I can recall hearing the term explosive bolts was in relation to the saturation TV coverage of the Apollo launches in the late 60s and early 70s. Explosive bolts seemed to be everywhere, releasing umbilicals and restraining the Saturn V launch stack on the pad. Young me pictured literal bolts machined from solid blocks of explosive and secretly hoped there was a section for them in the hardware store so I could have a little fun.

Pyrotechnic fasteners are mechanical fasteners (bolts, studs, nuts, etc.) that are designed to fail in a predictable fashion due to the detonation of an associated pyrotechnic device. Not only must they fail predictably, but they also have to be strong enough to resist the forces they will experience before failure is initiated. Failure is also typically rapid and clean, meaning that no debris is left to interfere with the parts that were previously held together by the fastener. And finally, the explosive failure can’t cause any collateral damage to the fastened parts or nearby structures.

Explosive bolt. Source: Ensign-Bickford Aerospace & Defense

Pyrotechnic fasteners fall into two broad categories. Explosive bolts look much like regular bolts, and are machined out of the same materials you’d expect to find any bolt made of. The explosive charge is usually internal to the shank of the bolt with an initiating device of some sort in the head. To ensure clean, predictable separation, there’s a groove machined into the bolt to create a shear plane.

Frangible nut and booster, post-use. Source: Space Junkie's Space Junk — Frangible nut and booster, post-use. Source: Space Junkie’s Space Junk

Frangible nuts are another type of pyrotechnic fastener. These tend to be used for larger load applications, like holding down rockets. Frangible nuts usually have two smaller threaded holes adjacent to the main fastener thread; pyrotechnic booster charges split the nut across the plane formed by the threaded holes to release the fastener cleanly.

“Eject! Eject! Eject!”

Holding back missiles is one thing, but where pyrotechnic fasteners save the most lives might be in the cockpits of fighter jets around the world. When things go wrong in a fighter, pilots need to get out in a hurry. Strapping into a fighter cockpit is literally sitting on top of a rocket and being surrounded by explosives. Most current seats are zero-zero designs — usable at zero airspeed and zero altitude — that propel the seat and pilot out of the aircraft on a small rocket high enough that the parachute can deploy before the pilot hits the surface. Dozens of explosive charges take care of ripping the aircraft canopy apart, deploying the chute, and cutting the seat free from the parachuting pilot, typically unconscious and a couple of inches shorter from spinal disc compression after his one second rocket ride.

https://www.youtube.com/watch?v=Z1cnvJO1TF8

Behind the Wheel

There’s little doubt that airbags have saved countless lives since they’ve become standard equipment in cars and trucks. When you get into a modern vehicle, you are literally surrounded by airbags — steering wheel, dashboard, knee bolsters, side curtains, seatbelt bags, and even the rear seat passenger bags. And each one of these devices is a small bomb waiting to explode to save your life.

When we think of explosives we tend to think of substances that can undergo rapid oxidation with subsequent expansion of hot gasses. By this definition, airbag inflators aren’t really explosives, since they are powered by the rapid chemical decomposition of nitrogenous compounds, commonly sodium azide in the presence of potassium nitrate and silicon dioxide. But the difference is purely academic; anyone who has ever had an airbag deploy in front of them or watched any of the “hold my beer and watch this” airbag prank video compilations will attest to the explosive power held in that disc of chemicals.

When a collision is detected by sensors connected to the airbag control unit (ACU), current is applied to an electric match, similar to the engine igniters used in model rocketry, buried within the inflator module. The match reaches 300°C within a few milliseconds, causing the sodium azide to rapidly decompose into nitrogen gas and sodium. Subsequent reactions mop up the reactive byproducts to produce inert silicate glasses and add a little more nitrogen to the mix. The entire reaction is complete in about 40 milliseconds, and the airbags inflate fully within 80 milliseconds, only to deflate again almost instantly through vent holes in the back of the bag. By the time you perceive that you were in an accident, the bag hangs limply from the steering wheel and with any luck, you get to walk away from the accident.

Grid Down

We’ve covered a little about utility poles and all the fascinating bits of gear that hang off them. One of the pieces of safety gear that lives in the “supply space” at the top of the poles is the fuse cutout, or explosive disconnector. This too is a place where a small explosion can save lives — not only by protecting line workers but also by preventing a short circuit from causing a fire.

Cutouts are more than just fuses, though. Given the nature of the AC transmission and distribution grid, the lines that cutouts protect are at pretty high voltages of 11 kV or more. That much voltage means the potential for sustained arcing if contacts aren’t rapidly separated; the resulting plasma can do just as much if not more damage than the short circuit. So a small explosive cartridge is used to rapidly kick the fuse body of a cutout out of the frame and break the circuit as quickly as possible. Arc suppression features are also built into the cutout to interrupt the arc before it gets a chance to form.

[Big Clive] recently did a teardown of another piece of line safety gear, an 11 kV lightning arrestor with an explosive disconnector. With a Dremel tool and a good dose of liquid courage, he liberated a carbon slug from within the disconnector, which when heated by a line fault ignites a .22 caliber charge similar to those used with powder actuated fastener tools. The rapid expansion of gasses ruptures the cases of the disconnector and rapidly breaks the circuit.

Conclusion

We’ve covered a few of the many ways that the power of expanding gas can be used in life safety applications. There are other ways, too — snuffing out oil field fires comes to mind, as does controlled demolition of buildings. But the number of explosives protecting us from more common accidents is quite amazing, all the more so when you realize how well engineered they are. After all, these everyday bombs aren’t generally blowing up without good reason.

Hands On With The First Open Source Microcontroller

January 5, 2017 by Brian Benchoff 148 Comments

2016 was a great year for Open Hardware. The Open Source Hardware Association released their certification program, and late in the year, a few silicon wizards met in Mountain View to show off the latest happenings in the RISC-V instruction set architecture.

The RISC-V ISA is completely unlike any other computer architecture. Nearly every other chip you’ll find out there, from the 8051s in embedded controllers, 6502s found in millions of toys, to AVR, PIC, and whatever Intel is working on are closed-source designs. You cannot study these chips, you cannot manufacture these chips, and if you want to use one of these chips, your list of suppliers is dependent on who has a licensing agreement with who.

We’ve seen a lot of RISC-V stuff in recent months, from OnChip’s Open-V, and now the HiFive 1 from SiFive. The folks at SiFive offered to give me a look at the HiFive 1, so here it is, the first hands-on with the first Open Hardware microcontroller.

Continue reading “Hands On With The First Open Source Microcontroller” →

Maintenance, Emissions, And Privacy: The OBD Story

January 4, 2017 by Bryan Cockfield 113 Comments

The 90s were a pivotal time in world history, and 1996 was no different. You might have spent the year glued to the TV playing Super Mario 64, or perhaps you were busy campaigning for Bill Clinton or Bob Dole, or maybe you were so depressed that Princess Diana and Prince Charles divorced that you spent the whole year locked in your room, a prisoner of your own existential nihilism. Whatever you did, though, it’s likely that one major event passed you by without a thought: The standardization of on-board vehicle diagnostics (in the US), otherwise known as OBD-II.

In the 1970s, vehicles (in some western countries, at least) were subject to ever-increasing restrictions on emissions. Most companies began switching from carburetors to efficient fuel injection systems, but even that wouldn’t be enough for the new standards. Cars began to carry rudimentary computer systems to manage and control the influx of valves, meters, and sensors that became the new norm. And, as one would guess, every car company had their own standard for managing and monitoring these computer systems. Eventually they would settle on the OBD system that we have today.

Continue reading “Maintenance, Emissions, And Privacy: The OBD Story” →

Derek Schulte: Path Planning For 3D Printers

January 3, 2017 by Elliot Williams 54 Comments

[Derek Schulte] designed and sells a consumer 3D printer, and that gives him a lot of insight into what makes them tick. His printer, the New Matter MOD-t, is different from the 3D printer that you’re using now in a few different ways. Most interestingly, it uses closed-loop feedback and DC motors instead of steppers, and it uses a fairly beefy 32-bit ARM processor instead of the glorified Arduino Uno that’s running many printers out there.

The first of these choices meant that [Derek] had to write his own motor control and path planning software, and the second means that he has the processing to back it up. In his talk, he goes into real detail about how they ended up with the path planning system they did, and exactly how it works. If you’ve ever thought hard about how a physical printhead, with momentum, makes the infinitely sharp corners that it’s being told to in the G-code, this talk is for you. (Spoiler: it doesn’t break the laws of physics, and navigating through the curve involves math.)

Continue reading “Derek Schulte: Path Planning For 3D Printers” →

Thermoacoustic Engine Has Only One Moving Part

January 3, 2017 by Manuel Rodriguez-Achach 21 Comments

Modern internal combustion engines have around 500 parts, with many of them moving in concert with the piston. But have you seen an engine with only one moving part, out of four in total? In the thermoacoustic engine, the power piston is the only part in motion. [YTEngineer] has built a very simple prototype that works on power provided by a tealight.

His little engine, slightly larger than a cigarette lighter, is composed of a test tube that serves as the cylinder, a smaller tube, called the choke, that fits inside the test tube, the stack, which is nothing more than some steel wool, and the power piston. [YTEnginer] nicely explains how the engine works: basically a temperature difference is used to induce high-amplitude sound waves that create the piston’s back-and-forth movement. The engine can be easily converted to an electricity generator by adding a magnet to the piston and a coil surrounding it.

The thermoacoustic engine is a particular type of Stirling engine. They have been proposed as electricity generators for space travel using radioisotopes as the heat source, among other applications. You may be interested in the history of Stirling engines, or perhaps even build a simple one.

Continue reading “Thermoacoustic Engine Has Only One Moving Part” →

A Singing Arc Lighter

January 2, 2017 by Anool Mahidharia 54 Comments

We’ve all been guilty of buying things we want, but don’t need. And that’s how [PodeCoet] found himself in possession of a couple of double-arc electric lighters, thanks to those far-eastern websites purveying cheap goods. ‘Tis the season of giving after all, justified [PodeCoet]. Being a hacker, the obvious thing to do was to make them belt out tinny tunes. If you’re still holding on to your gas lighters, don’t — because these electric ones are ‘oh so hackable’. Dual-arcs are the same, but twice the fun.

[PodeCoet] starts off with a tear down of the lighter, to figure out the schematic and understand how it works. There’s a charger IC for the LiPo, an unidentifiable micro-controller, a pair of FET’s driving a pair of power transistors, which in turn drive the HF output transformer at around 15.6kHz. He guesses that the “original micro-controller is probably an OTP part like a 12C508” but in the absence of a chipID he couldn’t be sure.

Instead of trying to break his head over it, he just swapped in a pin-compatible PIC12F1840. All that’s left to do is to write some quick-n-dirty code and sprinkle it with funny comments in order to modulate the output signal at audio frequencies. His first choice of tune was “We are Number One” by Lazy Town, the Icelandic educational musical comedy children’s television series (phew). But redditors are awesome, and someone asked him to add the “Imperial March” and [PodeCoet] obliged.

Since he was going to gift these lighters, the sneaky hacker added a prank in the code. Every time the button is pressed for more than two seconds, it works as normally expected and a counter is incremented. On the 20th count, and for one time only, the tune is played. No amount of pressing the button will play the tune again, confounding the user to wonder if he was hallucinating. This also helps ensure the lighter does not self-destruct prematurely, since the output transformer is likely designed for low duty cycles. His blog post contains all of the information needed to do this hack along with handy tips to avoid the problems he faced. A “Happy Birthday” tune would be great when lighting some birthday candles, we think.

[PodeCoet] has a fancy for high voltage stuff – check out “Home built Stun Baton turns you into a cop from Demolition Man“. This man surely loves his pranks, as evidenced by “Hacking your Co-Workers Label Makers“. And the farce is strong in this one — “Student trolls anti-Arduino Prof with parasite MCU“.

Continue reading “A Singing Arc Lighter” →

RooBee One, An Open-source SLA/DLP 3D Printer

January 1, 2017 by Pedro Umbelino 24 Comments

[Aldric Negrier] is no stranger to the 3D printing world. Having built a few already, he designed and built an SLA/DLP 3D printer, named RooBee One, sharing the plans on Instructables. He also published tons of other stuff, like a 3D Printed Syringe Pump Rack and a 3D Scanning Rig And DIY Turntable. It’s really worth while going through his whole Instructables repository.

This open-source 3D printer was inspired by the Cristelia – SLA/LCD 3d printer and the Vulcanus MAX 3D printer (that he designed). RooBee One has an aluminium frame and an adjustable print area of 80x60x200 mm, with up to 150x105x200mm build volume using an ACER DLP projector. In addition, a fan on top of the printer was added to extract the toxic vapours outside and away from the printer operator. The electronics are based on the Arduino MEGA with the RAMPS 1.4 shield and one NEMA 17 stepper motor. As for the Arduino Mega firmware, [Aldric] choose to use Repetier, which he usually uses in his other printers.

The SLA resin he used is the Standard Blend Resin from Fun to Do Resins. These resins tend to release toxic airborne particles, so extra care should be taken to ventilate the area while printing and also do a proper cleaning afterwards.

You can get a glimpse of the printer making a small gear come to life in the following video:

Continue reading “RooBee One, An Open-source SLA/DLP 3D Printer” →