Let No Eyebrow Go Unsinged With A Wrist-Mounted Flamethrower

We’ll say it just once, and right up front: wrist-mounted flamethrowers are a bad idea. An itchy nose and a brief moment of forgetfulness while sporting one of these would make for a Really Bad Day. That said, this flaming gauntlet of doom looks like a lot of fun.

We’ve got to hand it to [Steve Hernandez] – he put a lot of work into the Flame-O-Tron 9000. Building on his prior art in the field, [Steve] went a bit further with this design. The principle is the same – butane plus spark equals fun – but the guts of this flamethrower are entirely new. A pipe bomb custom fuel tank is used rather than the stock butane can, and a solenoid valve controls fuel flow. Everything lives in a snazzy acrylic case that rides on a handmade leather bracer, and controls in the hand grip plus an Arduino allow the user to fire short bursts of flame or charge up for a real fireball. See what you think of the final product in the short video after the break; it sounds as though even if the fuel runs out, the high-voltage would make a dandy stun gun.

Maybe we should lay off the safety nagging on these wrist rockets. After all, we’ve seen many, many, many of them, with nary a report of injury.

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Shop-Made Pneumatic Cylinders From PVC And Plywood

You see a lot of pneumatic actuators in industrial automation, and for good reason. They’re simple, powerful, reliable, and above all, cheap. Online sources and fluid-power suppliers carry a bewildering range of actuators, so why would anyone bother to make their own pneumatic cylinders? Because while the commercial stuff is cheap, it’s not PVC and plywood cheap.

Granted, that’s not the only reason [Izzy Swan] gives for his DIY single-acting cylinder. For him it’s more about having the flexibility to make exactly what he needs in terms of size and shape. And given how ridiculously easy these cylinders are, you can make a ton of them for pennies. The cylinder itself is common Schedule 40 PVC pipe with plywood endcaps, all held together with threaded rod. [Izzy] cut the endcaps with a CNC router, but a band saw or jig saw would do as well. The piston is a plywood plug mounted to a long bolt; [Izzy] gambled a little by cutting the groove for the O-ring with a table saw, but no fingers were lost. The cylinder uses a cheap bungee as a return spring, but an internal compression spring would work too,. Adding a second air inlet to make the cylinder double-acting would be possible as well. The video below shows the cylinder in action as a jig clamp.

True, the valves are the most expensive part of a pneumatic system, but if nothing else, being able to say you made your own cylinders is a win. And maybe you’ll get the fluid-power bug and want to work up to DIY hydraulics.

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Op Amps Before Transistors: A 600V Vacuum Tube Monster

Op amps. Often the first thing that many learn about when beginning the journey into analog electronics, they’re used in countless ways in an overwhelmingly large array of circuits. When we think about op amps, images of DIPs and SOICs spring to mind, with an incredibly tiny price tag to boot. We take their abundance and convenience for granted nowadays, but they weren’t always so easy to come by.

[Mr Carlson] serves up another vintage offering, this time in the form of a tube op amp. The K2-W model he acquired enjoyed popularity when it was released as one of the first modular general purpose amplifiers, due to its ‘compact form’ and ‘low price’. It also came with large application manuals which helped it to gain users.

In order to power up the op amp and check its functionality, +300V and -300V supplies are needed. [Mr Carlson] is able to cobble something together, since it’s very apparent that he has an enviable stash of gear lying around. A 600V rail to rail supply is not something to be taken lightly, though it does give this particular model the ability to output 100V pk-pk without any distortion.

The op amp is set up as an inverting amplifier, and once powered on proves to work flawlessly. As always, the video is an entertaining watch, stuffed full of retro electronics trivia. We’re big fans of [Mr Carlson]’s work, and have previously written about his adventures with a colossal walk-in AM radio transmitter, as well as his restoration of a 1930s oscilloscope and subsequent transformer de-potting.

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A Stereo Tube Amp For Less Than $5

Many of us have aspirations of owning a tube amp. Regardless of the debate on whether or not tube audio is nicer to listen to, or even if you can hear the difference at all, they’re gorgeous to look at. However, the price of buying one to find out if it floats your boat is often too high to justify a purchase.

A motor transformer

[The Post Apocalyptic Inventor] has built a stereo tube amplifier in the style of the Fallout video games. The idea came when he realised that the TK 125 tape recorder manufactured by Grundig was still using tube audio in the late 60s. What’s more, they frequently sell on eBay for 1-10€ in Germany. [TPAI] was able to salvage the main power amplifier from one of these models, and restore it so that it could be re-purposed and see use once more.

The teardown of the original cassette recorder yields some interesting parts. Firstly, an integrated motor transformer — an induction motor whose stator acts as the magnetic core of the transformer responsible for the tube electronics. There’s also an integrated capacitor which contains three separate electrolytics. The video after the break is well worth a watch (we always find [TPAI]’s videos entertaining).

A new chassis is created out of a steel base plate and aluminium angle, and some neat frames for the motor transformers are made from scrap copper wire bent and soldered together. It looks great, though there’s always the option to use a cake tin instead.

If you’re interested in the design of tube amps, we’ve covered heaps of cool builds: from this low-voltage design to this tiny guitar amp, or even ones using tubes which are flat.

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Teardown: Box of Pain (Gom Jabbar Sold Separately)

I immediately felt uncomfortable when I realized this thing is called the “Breo iPalm520 Acupressure Hand Massager”. You’re supposed to stick your hand into it, and through unknown machinations it performs some kind of pressure massage complete with heating action. It’s like one of those pain boxes from Dune. It’s all the more disturbing when you realize the red button on the thing is an emergency release. That’s right, once your hand is in this contraption you can’t take it out until the thing has had its way with you or you tap out.

Press to administer the Gom Jabbar

At least once a week I try to get to the local thrift store to look for interesting things. I’d like to be more specific than “interesting things”, but truth be told, I never really know what I’m looking for until I see it. Sure there’s the normal consumer electronics kind of stuff, but I’ve also found some very nice laboratory equipment, computer parts, software, technical books, etc. You just have to go regularly and keep an eye out for the occasional needle amongst the hay.

I want you to know, Dear Readers, that I did briefly summon the courage to put my hand into this thing and turn it on. Now I am not what one might call an overly brave man, and perhaps that might explain my personal experience. But when it started to hum and heat up, constricting around my hand to the point I couldn’t move my fingers, I screamed like a child and mashed the emergency button as if I was a pilot trying to eject from a mortally wounded aircraft. As far as Frank Herbert is concerned, I’m no human at all.

In an effort to better understand this torture device, lets open it up and see what lurks beneath that futuristic exterior.

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Battery-Powered Watering Timer Converted to Solar on the Cheap

Watering the garden or the lawn is one of those springtime chores that is way more appealing early in the season than later. As the growing season grinds along, a chore that seemed life-giving and satisfying becomes, well, just another chore, and plants often suffer for it.

Automating the watering task can be as simple as buying a little electronic timer valve that turns on the flow at the appointed times. [A1ronzo] converted his water hose timer to solar power. Most such timers are very similar, with a solenoid-operated pilot valve in line with the water supply and an electronic timer of some sort. The whole thing is quite capable of running on a pair of AA batteries, but rather than wasting money on new batteries several times a season, he slipped a LiPo pack and a charge controller into the battery case slot and connected a small solar panel to the top of the controller.

The LiPo is a nominal 3.7-volt pack, so he did a little testing to make sure the timer would be OK with the higher voltage. The solar panel sits on top of the case, and the whole thing should last for years. And bonus points for never having to replace a timer that you put away at the end of the season with batteries still in it, only to have them leak. Ask us how we know.

Like the best of hacks, this one is quick, easy and cheap — $15 in parts, aside from the timer. There are more complicated irrigation solutions, of course, one of which even won the Hackaday Prize once upon a time. But this one has us ordering parts to build our own right now.

Cams and Pushrods Improve 3D-Printed Compressed Air Engine

Some folks just can’t leave well enough alone, and that often ends up being a good thing. Such is the case with this 3D-printed compressed air engine, which just keeps getting better.

The design has changed a lot since we first covered [Tom Stanton]’s attempts at reviving the powerplant from the glory days of the Air Hogs line of toys, which he subsequently built a plane around. The engine was simple, with a ball valve that admitted air into the cylinder when a spring mounted to the top of the piston popped it out of the way. That spring has always bothered [Tom], though, compelling him to go back to the drawing board. He wanted to replace the ball valve with one actuated by a cam and pushrod. This would increase the complexity of the engine quite a bit, but with the benefit of eliminating the fail point of the spring. With a few iterations in the design, he was able to relocate the ball valve, add a cam to the crankshaft, and use a pushrod to open the valve. The new design works much better than the previous version, sounding more like a lawnmower than a 3D-printed engine should. Check out the design process and some tests in the video below.

And speaking of lawnmowers that run on compressed air

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