There’s not a huge amount of detail available in the video below, and no build log per se. But [Electron Dust] has a few shots in the video that explain what’s going on, as well as a brief description in a reddit thread about the device. The idea is to spin a ball up to a steady speed and release it the same way every time. The rig itself is made of wood and spun by plain brushed DC motors – [Electron Dust] explains that he chose them over PWM servos to simplify things and eliminate uncertainty in the release point. The ball is retained by a pair of arms, each controlled by a pair of hobby servos. An Arduino spins along with everything else and counts 50 revolutions before triggering the servos to retract and release the ball. A glass positioned at the landing spot captures the ball perfectly once everything is dialed in.
That’s a lot to unpack, but suffice it to say, all this stems from [Tom]’s obvious appreciation for physics. Where most of us would be satisfied with tossing a ball into the air and estimating the height to solve the classic kinematic equations from Physics 101, [Tom] decided that more extreme means were needed.
Having a compound trebuchet close at hand, a few simple mods were all it took to launch projectiles more or less straight up. The first payload was to be rocket-shaped, but that proved difficult to launch. So [Tom] 3D-printed an upsized golf ball and packed it with electronics to record the details of its brief ballistic flight. Aside from an altimeter, there’s a small servo controlled by an Arduino and an accelerometer. The servo retracts a pin holding the two halves of the ball together, allowing a parachute to deploy and return the package safely to Earth. The video below shows some pretty exciting launches, the best of which reached over 60 meters high.
Like most accidents, it happened in an instant that seemed to last an eternity. I had been felling trees for firewood all afternoon, and in the waning light of a cold November day, I was getting ready to call it quits. There was one tiny little white pine sapling left that I wanted to clear, no thicker than my arm. I walked over with my Stihl MS-290, with a brand new, razor sharp chain. I didn’t take this sapling seriously — my first mistake — and cut right through it rather than notching it. The tree fell safely, and I stood up with both hands on the saw. Somehow I lost my footing, swiveled, and struck my left knee hard with the still-running chainsaw. It kicked my knee back so hard that it knocked me to the ground.
In another world, that would likely have a been a fatal injury — I was alone, far from the house, and I would have had mere minutes to improvise a tourniquet before bleeding out. But as fate would have it, I was protected by my chainsaw chaps, full of long strands of the synthetic fiber Kevlar.
The chain ripped open the chaps, pulled the ultrastrong fibers out, and instantly jammed the saw. I walked away feeling very stupid, very lucky, and with not a scratch on me. Although I didn’t realize it at the time, I owed my life to Stephanie Kwolek.
Hawaiians started their weekend with quite a fright, waking up Saturday morning to a ballistic missile alert that turned out to be a false alarm. In between the public anger, profuse apologies from officials, and geopolitical commentary, it might be hard to find some information for the more technical-minded. For this audience, The Atlantic has compiled a brief history of infrastructure behind emergency alerts.
As a system intended to announce life-critical information when seconds count, all information on the system is prepared ahead of time for immediate delivery. As a large hodgepodge linking together multiple government IT systems, there’s no surprise it is unwieldy to use. These two aspects collided Saturday morning: there was no prepared “Sorry, false alarm” retraction message so one had to be built from scratch using specialized equipment, uploaded across systems, and broadcast 38 minutes after the initial false alarm. In the context of government bureaucracy, that was really fast and must have required hacking through red tape behind the scenes.
However, a single person’s mistake causing such chaos and requiring that much time to correct is unacceptable. This episode has already prompted a lot of questions whose answers will hopefully improve the alert system for everyone’s benefit. At the very least, a retraction is now part of the list of prepared messages. But we’ve also attracted attention of malicious hackers to this system with obvious problems in design, in implementation, and also has access to emergency broadcast channels. The system needs to be fixed before any more chaotic false alarms – either accidental or malicious – erode its credibility.
At some point, most of us have learned a little of the ancient art of origami. It’s a fascinating art form, and being able to create a recognizable model by simply folding paper in the right order can be hugely satisfying. Most of us move on to other pursuits once we master the classic crane model, but the mathematics behind origami can lead some practitioners past the pure art to more practical structures, like this folding ballistic barrier for law enforcement use.
The fifty-pound Kevlar and aluminum structure comes from Brigham Young University’s College of Mechanical Engineering, specifically from the Compliant Mechanisms Research program. Compliant mechanisms move by bending or deflecting rather than joints between discrete parts, and this ballistic shield is a great example. The mechanism is based on the Yoshimura crease pattern, which can be quickly modeled with a piece of paper. Scaling that up to a full-sized structure, light enough to be fielded but strong enough to stop a .44 Magnum round, was no mean feat. But as the video below shows, the prototype has a lot of potential.
Hackers tend to stash away lots of stuff that seems useless, right up until it saves the day. This includes not just junk in our parts bin but brains full of tips and tricks for the shop. With that in mind, you might want to file away a few of the tips in [AvE]’s video of how he made bulletproof glass for a rainy day.
By his own admission, [AvE]’s video is a little disjointed, and the topic of the bulletproof glass is only covered at the beginning and again briefly at the end. Most of the video concerns the machining of a stout stand for the glass for testing on the range. There’s plenty to learn from the machining, though, and [AvE] is always good for a laugh, so the video is worth a watch. The bulletproof glass itself is part of a long-term project that [AvE] is releasing first to his Patreon patrons – a ridiculously over-built flashlight dubbed “The Midnight Sun”. His first two tries at laminating the Lexan discs were less that optimal, as both brands of cyanoacrylate glue clouded the polycarbonate. Stay tuned to the end of the video for the secret of welding Lexan together into an optically clear sandwich.
As for testing under fire, [AvE] sent the rig off to buddy [TAOFLEDERMAUS] for the hot lead treatment. The video after the break shows that the glass is indeed bulletproof, as long as the bullet in question is a .22LR. Not so much for the 9mm, though – that was a clear punch-through. Still, pretty impressive performance for homebrew.
On this installment of Retrotechtacular we’re taking a look at the history of the United States Antiballistic Missile System. The cold war was a huge driver of technological development, and this missile defense is a good example. At its most basic this is a radar system capable of tracking objects in three dimensions. It utilizes separate transmitters and receivers which are synchronized to rotate at the same time.
The movie, which is about forty-five minutes, came to our attention because of [Dammitd’s] interest in the Luneburg Lens used by the system. At about 11:10 into the video after the break this component is discussed. Inside a dome like the one seen above is a reflector made of blocks of polystyrene foam which has been laced with bits of metal. This lens is stationary, with the receiver rotating around it to collect the transmitter’s waves as the echos bouncing off an object in the sky are focused by the lens.