On Point: The Yagi Antenna

If you happened to look up during a drive down a suburban street in the US anytime during the 60s or 70s, you’ll no doubt have noticed a forest of TV antennas. When over-the-air TV was the only option, people went to great lengths to haul in signals, with antennas of sometimes massive proportions flying over rooftops.

Outdoor antennas all but disappeared over the last third of the 20th century as cable providers became dominant, cast to the curb as unsightly relics of a sad and bygone era of limited choices and poor reception. But now cheapskates cable-cutters like yours truly are starting to regrow that once-thick forest, this time lofting antennas to receive digital programming over the air. Many of the new antennas make outrageous claims about performance or tout that they’re designed specifically for HDTV. It’s all marketing nonsense, of course, because then as now, almost every TV antenna is just some form of the classic Yagi design. The physics of this antenna are fascinating, as is the story of how the antenna was invented.

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Tightwad Hacks Label Printer, Beats Manufacturer at Own Game

Sometimes we hack for the thrill of making something new, and sometimes we hack to push back the dark veil of ignorance to shed fresh light on a problem. And sometimes, like when turning a used label printer into a point-of-sale receipt printer, we hack because we’re cheapskates.

We say that with the utmost respect and affection — there’s nothing to be ashamed of when your motive is strictly pecuniary. In [Dan Herlihy]’s case, hacking a cheap Brother label printer to use thermal paper meant saving $300 on a dedicated receipt printer. But it also meant beating Brother at their “Razor and Blades” business model that keeps you buying their expensive proprietary labels. A pattern of holes in the plastic label roll tells the printer what size labels are loaded, so [Dan] defeated that by breaking off a piece of the plastic and gluing it on the sensor. To convince the printer that plain thermal paper is label stock, he printed up a small strip of paper with the same pattern of black registration stripes that appear on the back of the labels. Pretty clever stuff, and it lets him print high-resolution receipts for his electronics shop on the seriously cheap.

[Dan]’s hack is simple, but may suffer from wear on the paper encoder strip. Perhaps this Brother hack using the gears as encoders will provide some inspiration for long-term fix.

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Custom Workstation Makes Plasma Cutting a Breeze

A plasma cutter is probably top of every metalworker’s short list of dream tools. From freehand curves to long straight cuts, nothing beats a plasma cutter for getting the creative juices flowing. Unfortunately, there’s also the jet of superheated metal blasting through the workpiece to deal with, which is the reason behind this shop-built plasma cutting workstation.

[Regalzack] looks like he had a couple of design goals in mind for his table. A solid work surface isn’t a great idea for plasma cutting, so he designed the top as a grid of replaceable steel slats. Underneath is a hopper to collect the slag, both for neatness and for fire safety. The table top and hopper live on a custom-built wheeled steel frame, and the lower shelf provides plenty of room for his Lincoln 375 plasma rig. With hooks for cables and a sturdy ground clamp tab, the whole thing is a nicely self-contained workstation. The video below shows the build and some of the fabrication techniques [Regalzack] used; we were especially taken by the clever way he cut the slots for the table slats.

Plasma is versatile stuff – you can use it to make music, cook a burger, or decorate wood. And it’s not too shabby for notching metal tubing either.

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Blacksmith’s Junkyard Power Hammer Packs a Punch

Any way you look at it, blacksmithing is a punishing trade. Heavy tools, a red-hot forge, flying sparks, and searing metal all exact a toll on the smith’s body unless precautions are taken. After proper safety equipment and good training, a blacksmith may want to invest is power hammer to replace at least some of the heavy hammer work needed to shape hot metal.

Power hammers aren’t cheap, though, which is why [70kirkster] built one from an old engine block. You’ve got to admire the junkyard feel of this thing; it’s almost nothing but scrap. The engine block is a straight-6 from an old Ford pickup stripped of everything but the crankshaft and one piston. An electric motor spins the crankshaft and moves the hammer against the anvil through connecting rods and a trip arm fashioned from a trailer leaf spring. Everything looks super solid and the hammer hits hard; the videos below tell the tale of the build and show the hammer in action. Not bad for $100 out-of-pocket.

Blacksmithing is one of those dark arts that really deserves to have more adherents. The barriers to entry can be high, but the rewards are great. Looking to get started on the cheap? Then check out [Bil Herd]’s guide to hacking together a backyard smithy.

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Custom Hydraulic Cylinders from Off-the-Shelf Components

When your project needs power, you might need to turn to hydraulics. There is a lot of mystery about fluid power, but there is also a huge supply chain devoted to getting you the parts you need to power your project. Off-the-shelf components may not fit your application though, in which case it might be handy to know how to build your own custom hydraulic cylinders.

While it’s true that custom cylinder builds are pretty common, it’s still interesting to see the process [MakeItExtreme] used. Starting with an off-the-shelf piston and gland, this double-acting cylinder build is a pretty straightforward exercise in machining. The cylinder is threaded at the rod end and a cap is welded onto the piston end. Threaded bosses for fittings are welded on, the business end of the rod is threaded, and everything is assembled. The cylinder turned out to be pretty powerful as the video below shows.

As a product of the prolific team at [MakeItExtreme], we can tell this cylinder is destined for another even more interesting build. It’s hard to guess where this one will end up, but we’ll bet it ends up in another tool in their shop. Maybe it end up powering a beefed-up version of their recent roll bender.

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Sense All the Things with a Synthetic Sensor

What will it take to make your house smarter than you? Judging from the price of smart appliances we see in the home centers these days, it’ll take buckets of cash. But what if you could make your home smarter — or at least more observant — with a few cheap, general purpose “supersensors” that watch your every move?

Sounds creepy, right? That’s what [Gierad Laput] and his team at the Carnegie Mellon Human-Computer Interaction Institute thought when they designed their broadband “synthetic sensor,” and it’s why they purposely omitted a camera from their design. But just about every other sensor under the sun is on the tiny board: an IR array, visible light sensors, a magnetometer, temperature, humidity, and pressure sensors, a microphone, PIR, and even an EMI detector. Of course there’s also a WiFi module, but it appears that it’s only for connectivity and not used for sensing, although it clearly could be. All the raw data is synthesized into a total picture of the goings on in within the platform’s range using a combination of machine learning and user training.

The video after the break shows the sensor detecting typical household events from a central location. It’s a powerful idea and we look forward to seeing how it moves from prototype to product. And if the astute reader recognizes [Gierad]’s name, it might be from his past appearance on these pages for 3D-printed hair.

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Self-assembling Polymers Support Silicone 3D Prints

We all know what the ultimate goal of 3D printing is: to be able to print parts for everything, including our own bodies. To achieve that potential, we need better ways to print soft materials, and that means we need better ways to support prints while they’re in progress.

That’s the focus of an academic paper looking at printing silicone within oil-based microgels. Lead author [Christopher S. O’Bryan] and team from the Soft Matter Research Lab at the University of Florida Gainesville have developed a method using self-assembling polymers soaked in mineral oil as a matrix into which silicone elastomers can be printed. The technique takes advantage of granular microgels that are “jammed” into a solid despite being up to 95% solvent. Under stress, such as that exerted by the nozzle of a 3D printer, the solid unjams into a flowing liquid, allowing the printer to extrude silicone. The microgel instantly jams back into a solid again, supporting the silicone as it cures.

[O’Bryan] et al have used the technique to print a model trachea, a small manifold, and a pump with ball valves. There are Quicktime videos of the finished manifold and pump in action. While we’ve covered flexible printing options before, this technique is a step beyond and something we’re keen to see make it into the hobby printing market.

[LonC], thanks for the tip.