Giant PC fan

3D-Printed Parts Let You Assemble Your Own Biggest Fan

It’s getting close to the time of year when we need to start carefully vetting projects here at Hackaday. After all, nobody likes to get punked by an early April Fool’s joke. But as silly as this outsized PC fan looks, it sure seems like a legit build, if a bit on the pointless side.

Then again, perhaps pointless is too harsh a word to use. This 500-mm fan is by [Angus] over at Maker’s Muse, and it represents a lot of design work to make it buildable, as well as workable and (mostly) safe. Using both CNC-cut MDF and printed parts, the fan is an embiggened replica of a normal-sized case fan. The fan’s frame had to be printed in four parts, which lock together with clever interlocking joints. Each of the nine blades locks into a central hub with sturdy-looking dovetails.

And sturdy is important, as the fan is powered by a 1,500 Watt brushless DC motor. With a 4:1 reduction thanks to a printed gear train, the fan spins at around 3,300 RPM, which makes a terrifying noise. There’s a little bit of “speed-wobble” evident, but [Angus] managed to survive testing. The fan, however, did not — the 3D-printed gears self-destructed after a full-speed test, but not before the fan did its best wind tunnel imitation. And the RGB LEDs looked great.

This one reminds up of something we might see [Ivan Miranda] come up with. In fact, his super-sized 3D printer might have been just the thing to shorten [Angus]’ print times.

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Homemade Toy Wind Tunnel Blows (Really Well)

Sometimes a kid wakes up on Christmas morning and runs downstairs, only hoping to see one thing: a shiny new wind tunnel. This past December, that’s exactly what [SparksAndCode]’s son found under beside the tree, complete with a bag of scarves, ping-pong balls, and other fun things to launch through it (in the name of physics, of course).

The real story here starts about a week before Christmas, when [SparksAndCode]’s son was enthralled by a similar device at a science museum. At his wife’s suggestion, [SparksAndCode] got to work designing a and building a wind tunnel with hardware-store parts, his deadline looming ahead. The basic structure of the tunnel is three rods which support plywood collars. The walls are formed by plastic sheets rolled inside the collars to make a tube. Underneath, a Harbor Freight fan supplies a nice, steady stream of air for endless entertainment.

After finding a few bugs during his son’s initial beta testing on Christmas morning, [SparksAndCode] brought the wind tunnel back into the shop for a few tweaks and upgrades, including a mesh cover on the air intake to stop things from getting sucked into the fan. The final result was a very functional (and fun!) column of air. Looking for even more function (but not necessarily less fun)? We’ve got you covered too with this home-built research wind tunnel from a few years back.

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The Air Multiplier Fan Principle, Applied To A Jet Engine

Many readers will be familiar with the Dyson Air Multiplier, an ingenious bladeless fan design in which a compressor pushes jets of air from the inside edge of a large ring. This fast-moving air draws the surrounding air through the ring, giving the effect of a large conventional fan without any visible moving parts and in a small package. It’s left to [Integza] to take this idea and see it as the compressor for a jet engine, and though the prototype you see in the video below is fragile and prone to melting, it shows some promise.

His design copies the layout of a Dyson with the compressor underneath the ring, with a gas injector and igniter immediately above it. The burning gas-air mixture passes through the jets and draws the extra air through the ring, eventually forming a roaring jet engine flame exhaust behind it. Unfortunately the choice of 3D print for the prototype leads to very short run times before melting, but it’s possible to see it working during that brief window. Future work will involve a non-combustible construction, but his early efforts were unsatisfactory.

It’s clear that he hasn’t created the equivalent of a conventional turbojet. Since it appears that its operation happens when the flame has passed into the center of the ring, it has more in common with a ramjet that gains its required air velocity with the help of extra energy from an external compressor. Whether he’s created an interesting toy or a useful idea remains to be answered, but it’s certainly an entertaining video to watch.

Meanwhile, this isn’t the first project we’ve seen inspired by the Air Multiplier.

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Air Extractor Automatically Gives AC A Boost

Portable air conditioning units are a great way to cool off a space during the hot summer months, but they require some place to blow the heat they’ve removed from your room. [VincentMakes] got a portable AC unit for his home, but he found that the place he wanted to put it was too far from the only window he could use to dump the hot air. Having too long of a duct on the hot air exhaust increases the back pressure on the fan which could cause it to prematurely fail, so [Vincent] used an extractor fan to automatically give is AC unit’s exhaust a boost on its way to the window.

Because his AC can operate at low, medium, and high speeds, he chose an extractor fan that also supported multiple speeds and took care to match the airflow of the AC and extractor fan to avoid putting too much strain on either fan. He designed a system to automatically set the speed of the boosting fan to match that of the AC using a Hall effect current sensor to measure the AC unit’s power draw and an Arduino Nano for control. A custom PCB interfaces the Nano to the Hall Sensor and control relays, and we have to applaud [Vincent] for keeping the +5V DC and 230V AC far, far away from each other. In addition to this fine electronics work, [Vincent] also built an enclosure for the fan controller that allows the fan to be mounted on top at an angle, which helps avoid having hard bends in the exhaust duct.

If this has you thinking about smart air conditioners to keep cool this summer, check out this ESP8266-powered smart AC system, or this Raspberry Pi-based system that controls both AC and blinds!

Shop Exhaust Fan Salvaged From Broken Microwave

You don’t have to look hard to find a broken microwave. These ubiquitous kitchen appliances are so cheap that getting them repaired doesn’t make economical sense for most consumers, making them a common sight on trash day. But is it worth picking one of them up?

The [DuctTape Mechanic] certainly thinks so. In his latest video, he shows how the exhaust fan from a dead microwave can easily and cheaply be adapted to blow smoke and fumes out of your workshop. While it’s obviously not going to move as much air as some of the massive shop fans we’ve covered over the years, if you’re working in a small space like he is, it’s certainly enough to keep the nasty stuff moving in the right direction. Plus as an added bonus, it’s relatively quiet.

Now as you might expect the exact internal components of microwave ovens vary wildly, so there’s no guarantee your curbside score is going to have the same fan as this one. But the [DuctTape Mechanic] tries to give a relatively high-level overview of how to liberate the fan, interpret the circuit diagram on the label, and wire it up so you can plug it into the wall and control it with a simple switch. Similarly, how you actually mount the fan in your shop is probably going to be different, though we did particularly like how he attached his to the window using a pair of alligator clips cut from a frayed jumper cable.

Got a donor microwave but not in the market for a impromptu shop fan? No worries. We recently saw a dud microwave reborn as a professional looking UV curing chamber that would be the perfect partner for your resin 3D printer. Or perhaps you’d rather turn it into a desktop furnace capable of melting aluminum, copper, or bronze.

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jellyandmarshmallows windTunnel close-up

Perfecting Paper Planes Peering Past Perspex Portals

This wind tunnel is a pile of junk and we love it! When making science and engineering accessible to kids, it really helps to show that it doesn’t require a fancy research lab. [Jelly & Marshmallows] show kids that it takes little more than cardboard, duct tape, and dumpster-diving to up your paper airplane game to NASA levels of engineering.

[Jelly & Marshmallows] built their wind tunnel for a Maker Faire using the aforementioned cheap and free materials for the straightener, collector, diffuser, and fan sections. We especially love the efficient hack of using stacked ceiling light diffusers rather than hundreds of straws for the straightener.


The most time went into the working section, custom-built from plywood frames and acrylic windows. Many 3D printed parts came together to convert a smoke-ring gun to emit smoke trails and LEDs were employed to make those trails a little easier to see. We think the magnetic clips for quick changes of aircraft and their position along a steel ruler were inspired.

The kids attending the Maker Faire (we miss those!) loved the exhibit, having the best time hitting a big green arcade button to spin up the fan. It’s the little things in life. How would you get the kids even more involved with analyzing aerodynamics and make the smoke trails more visible?


Thanks for the tip [Rómulo Antão]

The Dynamotor Simplified

[Robert Murray-Smith] doesn’t like the price of inverters to convert DC to AC. That led him to build a dynamotor, or what is sometimes called a motor-generator set. These devices are just DC motors driving a generator. Of course, motors can also be used as generators and [Robert] had a stack of brushless motors in the form of PC fans. A two-fan dynamotor was born.

The brushless motors are attractive because, traditionally, the brushes are what usually fail on a dynamotor. The fan that will act as a generator needs some surgery, but it is simple. He scraped off all the control electronics and connected wires to the coils to form a three-phase generator. There’s no need for the fan blades in that configuration, either. If you were using ordinary motors and a generator, getting shafts concentric would be an important task. With the fans, it is simple to just line up the mounting holes and you get perfect alignment for free.

How does it work? [Robert] has a second video showing the output on a scope. You can see both videos below. The dynamotor makes a good-looking sine wave, probably much better than most reasonable-priced solid state inverters. He didn’t mention how much current he could successfully draw, but it probably isn’t much. You’d also need a transformer to replace a commercial inverter that would put out line voltage, so that would be some more loos in the system. On the other hand, if you wanted AC at a lower voltage, you might just replace all the transformers, if you were building a piece of gear yourself.

We’ve looked at how these things work in some detail. There were common in old tube radios, particularly military ones.

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