A FET Oscilloscope Probe For Higher Frequencies

April 23, 2022 by Jenny List 8 Comments

It’s a problem that has dogged electronic engineers since the first electrons were coaxed along a wire: that measuring instruments can themselves disrupt the operation of a circuit. Older multimeters for example had impedances low enough to pull resistor values, thus our multimeters today have high-impedance FET inputs. [Christoph] faced it with his oscilloscope probe, its input capacitance was high enough to put unacceptable load on a crystal oscillator and stop it oscillating. He thus built a FET input probe for higher RF frequencies, and its construction is an accessible view of wideband RF instrumentation design.

The circuit is a very simple one using a dual-gate FET, but the interest comes in the PCB and screening can design to ensure good RF performance. Off-the-shelf cans have four sides, so to accommodate the circuit one wall of the can had to be removed. The end result is a tiny PCB with miniature co-ax connectors for power and signal, which when characterised was found to have a 1.3 GHz bandwidth and a very low input capacitance.

If the language of RF design is foreign to you, may we recommend [Michael Ossmann]’s talk at a Superconference a few years ago.

Riding Mower CVT Upgrade Really Gets Things Moving

April 23, 2022 by Tom Nardi 6 Comments

As we’ve learned from past experience, videos from [HowToLou] tend to be a bit controversial. His unique style of expedient engineering isn’t everyone’s cup of tea, especially when it’s combined with a devil-may-care attitude towards safety. On the other hand, there’s no arguing that his methods get results. His video on converting an 18 HP riding mower into something akin to a go-kart is a perfect example.

The first phase of the project involves removing all the hardware related to mowing, as obviously you won’t be cutting any grass while pushing speeds of 48 kph (30 mph). This both saves weight, and removes a lot of mechanical complication that would be in the way of further modification. That said, it also leaves the mower immobile, as there’s no longer be any connection between the engine and transaxle.

The new drivetrain features some beefy bracing.

In its place, [HowToLou] installs an off-the-shelf torque converter kit that uses a continuously variable transmission (CVT) clutch. As he quickly demos, the CVT technology allows the gear ratio to automatically adapt to the engine RPM thanks to pulleys that change their size depending on how fast they’re spinning. It’s a big improvement over the system he originally yanked out, though as you might expect, fitting it into the mower required some custom work. The final step was to pull the old pulley off of the transaxle and replace it with one that’s less than half the original size.

Wearing his protective flip-flops, [HowToLou] hops on the souped-up mower and is nearly thrown off the back of it as soon as he steps on the gas. Clearly the modifications were a success, and the video ends with some open road testing — presumably he’s riding off to the store to go buy a helmet.

We actually missed this video when it first made the rounds, but it has since picked up steam and is pulling in some impressive numbers. [HowToLou] tells us he thinks it’s due to the fact that a lot of people are upgrading to more modern zero-turn mowers, meaning there’s a surplus of these second-hand mini tractors on the market. Whatever the reason, we’re happy to see this backyard engineer get some mainstream success; his methods might not always be by the book, but they’re always entertaining.

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Retrotechtacular: The Power To Stop

April 23, 2022 by Dan Maloney 22 Comments

In everyday life, the largest moving object most people are likely to encounter is probably a train. Watching a train rolling along a track, it’s hard not to be impressed with the vast amount of power needed to put what might be a mile-long string of hopper cars carrying megatons of freight into motion.

But it’s the other side of that coin — the engineering needed to keep that train under control and eventually get it to stop — that’s the subject of this gem from British Transport Films on “The Power to Stop.” On the face of it, stopping a train isn’t exactly high-technology; the technique of pressing cast-iron brake shoes against the wheels was largely unchanged in the 100 years prior to the making of this 1979 film. The interesting thing here is the discovery that the metallurgy of the iron used for brakes has a huge impact on braking efficiency and safety. And given that British Railways was going through about 3.5 million brake shoes a year at the time, anything that could make them last even a little longer could result in significant savings.

It was the safety of railway brakes, though, that led to research into how they can be improved. Noting that cast iron is brittle, prone to rapid wear, and liable to create showers of dangerous sparks, the research arm of British Railways undertook a study of the phosphorus content of the cast iron, to find the best mix for the job. They turned to an impressively energetic brake dynamometer for their tests, where it turned out that increasing the amount of the trace element greatly reduced wear and sparking while reducing braking times.

Although we’re all for safety, we have to admit that some of the rooster-tails of sparks thrown off by the low-phosphorus shoes were pretty spectacular. Still, it’s interesting to see just how much thought and effort went into optimizing something so seemingly simple. Think about that the next time you watch a train go by.

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2022 Sci-Fi Contest: Your Home Assistant, HAL 9000

April 23, 2022 by Lewin Day 17 Comments

Anyone who has seen 2001: A Space Odyssey will easily remember HAL 9000, the sentient computer that turned against its human companions aboard Spacecraft Discovery One. [Ben Brooks] decided to recreate the foreboding digital being, and put it to work as a smart home assistant.

The build consists of a 3D printed assembly that looks very much like HAL did in the movie. It runs as a standalone device hooked up to [Ben]’s Home Assistant instance, a self-hosted home automation solution. The device is capable of playing sound clips from the movie, with the help of an ESP8266 and a DF Player Mini module. It’s triggered by a button or motion sensor, but it’s also hooked up to Home Assistant for some extra smarts. This setup makes sure HAL stays silent when a Chromecast is playing content on TV, so as not to disturb essential viewing.

Overall, it’s a fun movie tribute build that is remarkably true to the source material. Let’s just hope this HAL doesn’t get any maniacal ideas, forcing [Ben] to pull apart its processor to stop its dangerous machinations.

We’ve seen some other great HAL builds before, too. Video after the break.

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A Universal, Non-planar Slicer For 3D Printing Is Worth Thinking About

April 23, 2022 by Donald Papp 28 Comments

One may think that when it comes to 3D printing, slicing software is pretty much a solved problem. Take a 3D model, slice it into flat layers equal to layer height, and make a toolpath so the nozzle can create those layers one at a time. However, as 3D printing becomes more complex and capable, this “flat planar slicing” approach will eventually become a limitation because a series of flat slices won’t necessarily the best way to treat all objects (nor all materials or toolheads, for that matter.)

How a 20 mm cube looks when sliced in a cone-shaped plane.

[René K. Müller] works to re-imagine slicing itself, and shows off the results of slicing 3D models using non-planar geometries. There are loads of pictures of a 20 mm cube being sliced with a variety of different geometries, so be sure to give it a look. There’s a video embedded below the page break that covers the main points.

It’s all forward-thinking stuff, and [René] certainly makes some compelling points in favor of a need for universal slicing; a system capable of handling any geometry, with the freedom to process along any path or direction. This is a concept that raises other interesting questions, too. For example, when slicing a 20 mm cube with non-planar geometries, the resulting slices often look strange. What’s the best way to create a toolpath for such a slice? After all, some slicing geometries are clearly better for the object, but can’t be accommodated by normal hot ends (that’s where a rotating, tilted nozzle comes in.)

Such worries may not be an issue for most users at the moment, but it’s worth trying to get ahead of the curve on something like this. And lest anyone think that non-planar slicing has no practical purpose, we previously covered [René]’s demonstration of how non-planar slicing can reliably create 90° overhangs with no supports.

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Research: It’s Like Cheating, But Fair

April 23, 2022 by Elliot Williams 53 Comments

My niece’s two favorite classes in high school this year are “Intro to AI” and “Ethical Hacking”. (She goes to a much cooler high school than I did!) In “Hacking”, she had an assignment to figure out some bug in some body of code. She was staring and staring, figuring and figuring. She went to her teacher and said she couldn’t figure it out, and he asked her if she’d tried to search for the right keywords on the Internet.

My niece responded “this is homework, and that’d be cheating”, a line she surely must have learned in her previous not-so-cool high school. When the teacher responded with “but doing research is how you learn to do stuff”, my niece was hooked. The class wasn’t abstract or academic any more; it became real. No arbitrary rules. Game on!

But I know how she feels. Whether it’s stubborn independence, or a feeling that I’m cheating, I sometimes don’t do my research first. But attend any hacker talk, where they talk about how they broke some obscure system or pulled off an epic trick. What is the first step? “I looked all over the Internet for the datasheet.” (Video) “I found the SDK and that made it possible.” (Video) “Would you believe this protocol is already documented?” In any serious hack, there’s always ample room for your creativity and curiosity later on. If others have laid the groundwork for you, get on it.

If you have trouble overcoming your pride, or NIH syndrome, or whatever, bear this in mind: the reason we share information with other hackers is to give them a leg up. Whoever documented that protocol did it to help you. Not only is there no shame in cribbing from them, you’re essentially morally obliged to do so. And to say thanks along the way!

Omnibot Shows Off Over A Decade Of CNC Prowess

April 23, 2022 by Ryan Flowers 17 Comments

At first glance, you might think the Omnibot v3 wasn’t anything more than a basic 3D printed robotics platform, but you’d be wrong on both counts. There’s actually no 3D printed parts on the build, and while you could describe the platform as simplistic, calling it basic certainly doesn’t do the clever design justice. In the video after the break, creator [Michal] takes us through the process of designing and building this high quality bot.

The build starts with huge amounts of time and effort in a CAD program designing the Omnibot v3 with its four wheel steering and ability to do fancy things like spin in place. With the CAD and 3D renders out of the way, the process of transforming the digital into the physical began with a CNC router.

Rather than routing the individual components out of a suitable material, [Michal] cut forms. Those forms were made only for the creation of silicone molds. Those silicon molds where then used to pour the actual parts with polyurethane resin. It is these resin parts that make up the actual Omnibot v3, which is manually demonstrated at the end of the video.

All in all, it’s a neat project with a neat process. If we were to stop here, things would be mostly complete and you’d click on to the next great Hackaday article. But there’s more to be had here. You see, [Michal] is also fellow behind the Guerrilla guide to CNC and resin casting. In his own words: “CNC machining and resin casting are an underappreciated method for producing engineering-grade parts, but the process is fast, predictable, and garage-friendly.” After seeing the results, we can’t help but to agree.

By the way, before anybody in the comments can yell “DUPE!”, we already know. You see, we featured the Guerrilla guide to CNC and resin casting once before, almost exactly 11.5 years ago! It’s been updated since then, and appears to be an absolute gold mine of information for anybody wanting to walk in [Michal]’s shoes.

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