Like A Wire Bender, But For Pop Tubes

Are you familiar with pop tubes? Resembling the corrugated section of a bendy straw, they are at the core of PopTuber, an intriguing research project from the Actuated Experience Lab at the University of Chicago.

With five motors and specialized gears a pop tube can be formed into complex, arbitrary shapes, and just as easily reset.

PopTuber shows how five motors and some specialized gears are all it takes to bend pop tubes into complex and stable 3D shapes. One can design the shapes in software, feed a pop tube into the shaper, and watch the device do the work. Importantly, the device can just as easily reset and re-use the tube. Watch the video (embedded below the page break) to see it in action and get a feel for what it can do.

In concept, it’s a little like a wire-bending machine, although wire benders are bulkier in comparison, more complex to scale, and unbending a wire is a separate process with its own hardware.

This project explores possibilities for a machine that can crank out complex curves on demand, such as oddball user interfaces, physical prototyping, and even a strange sort of physical display. But the real forward-thinking and interesting question researchers asked is whether this idea could be a form of programmable matter. The project shows that five actuators in a relatively compact package are all that’s needed to shape (and reset) a pop tube of arbitrary length in a programmable way, and it can scale easily to different sizes.

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3D Printing Space Cadet Pinball Into The Real World

Unless you’ve managed to avoid touching a Windows computer until after the Windows XP era, it’s pretty good odds you’ve played Space Cadet Pinball. Some of you may have even paid for the Mac port of Full Tilt! Pinball, the actual game the Windows freebee was supposed to demo. Unofficial ports exist for Linux as well, which means the one place nobody has ever played the game is, ironically, on a pinball table. [CNCDan]aims to change that in a video embedded below.

Ironically given [CNCDan]’s name, the parts he starts with — the two sorts of pop bumpers, the drop targets, slingshots, and delayed-drop hole– are all largely 3D-printed. While some of these parts are available commercially, it turns out that the scaling of the virtual pinball machine doesn’t match anything on offer, and rather than compromise [CNCDan] decided to do it himself, an attitude we absolutely respect.

All that’s left are the flippers– his first prototype wasn’t powerful enough–and a couple minor mechanisms before building the table. To do that, he’ll need high-resolution art worth printing. Not surprisingly, a game dating from 1995 doesn’t have high resolution assets available with which to do that. That kind of creativity isn’t in [CNCDan]’s wheelhouse, so if it is in yours and you want to collaborate, or know someone who does, you can reach [CNCDan] at his YouTube page. At the very least, he can pay you in playtime.

[CNCDan] often goes beyond his namesake, like with his SteamDeck-like handheld, or his 3D printed VR headset. Still, no guesses how he’s going to build the cabinet.

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Water-cooling A 3D Printed Rocket Isn’t Quite Practical

Consumer-grade 3D printers are useful for lots of things, but they kind of fall down when it comes to making stuff that survives high temperatures. [Mr. More Gooder] wasn’t deterred from a rocket build using FDM printed parts though, instead relying on water cooling to try and beat this practical limit.

The concept is simple enough—[Mr. More Gooder] printed a propane-burning combustion chamber and nozzle out of plastic that you’d totally expect to melt when the flames started. Thus, the nozzle was given fittings to allow water to be continually pumped through to try and drag away enough heat to let the rocket survive more than a few seconds. Unfortunately, during testing the uncooled combustion chamber quickly melted. A redesign with water cooling throughout performed a little better, until the water jacket began to leak into the main chamber and extinguished the flames. Melted plastic could be seen dripping out of the nozzle shortly after ignition, too.

Even if the nozzle did hold up for a longer period of time, it’s worth noting this is probably not a viable route towards a flight-ready engine. Mostly because you would need a huge supply of water to keep the components cool which would add a great deal of weight to any such build. There’s a reason NASA doesn’t recycle old drink bottles to make rocket engines, after all.

In any case, we love to see all sorts of rocket experiments, even the unsuccessful ones.

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Biofeedback Butterfly Beats With A Pulse

Biofeedback is the idea of making one conscious of a biological process or feature, and then using this to try and exert control over the very same. [Mariia Hruntes] demonstrates this ably with a fluttering build of her own design.

In this case, the biological process being made clear is that of the user’s heartbeat. This is tracked with a MAX30102 pulse oximetry sensor, which can be used to measure both heart rate and blood oxygen levels if so desired. It’s hooked up to an Arduino Uno, which polls for pulse rate data, and then actuates an SG90 micro servo in turn. This operates the wings of a 3D printed butterfly, such that they flap in pace with the wearer’s pulse. The goal is to observe this, and then try and calm one’s self to relax and slow the flapping through the power of the mind.

It’s a simple build, but one that clearly demonstrates the concepts of biofeedback in action. We’ve seen similar principles applied to everything from aiding sleep to improving the practice of mediation. If you’re working on your own neat biofeedback project, be sure to let us know on the tipsline.

How To Avoid Failed Screw Holes In 3D Printed Parts

Screws are useful fasteners for 3D prints, but the effectiveness of a screw (not to mention the ease or hassle of insertion) depends on the hole itself. This comprehensive guide on how to design screw holes in 3D printed parts takes guesswork out by providing reference tables as well as useful general tips.

The guide provides handy tables saying exactly how big to design a hole depending on screw type, material (PLA, PETG, or high-flow PETG) and whether the hole is printed in a vertical or horizontal orientation. This takes the guesswork out of screw hole design.

There’s no reason to guess the right size of hole for a screw, just refer to some handy tables.

The reason for different numbers is because multiple (but predictable) variables affect a 3D-printed hole’s final dimensions. Shrinkage, filament properties, and printing orientation can all measurably affect small features like screw holes; accounting for these is the difference between a good fit, and cracking or stripping.

In addition to the tables, there are loads of other useful tips. Designing lead-ins makes screws easier to insert and engage, and while increasing walls is an easy way to add strength it’s also possible to use 3D-printed microfeatures which are more resistant to distortion and don’t depend on slicer settings. There’s even suggested torque amounts for different screw and material types.

Sure, the most reliable way to get a hole of a known size is to drill it out yourself. But that’s an extra step, and drill bits aren’t always at hand in the desired sizes. The guide shows that it is entirely possible to print an ideal screw hole by taking a few variables into account.

If your design calls for screws, be sure to check it out and see if there’s anything you can use in your own designs.

3D Printed Train Whistles Sound Out At Full Scale

The age of steam is long gone, but there are few railfans who don’t have a soft spot for the old rolling kettles. So you’d best believe when [AeroKoi] talks about 3D printed train whistles, that’s steam whistles. Generally speaking, Diesels have horns.

You would not expect printed plastic to hold up to live steam– but that’s why [AeroKoi] uses compressed air. Besides, it’s a lot easier to both justify and maintain an air compressor than a boiler in the shop. At least some hobbyists say it doesn’t make a huge difference with brass whistles, so it should be good enough for plastic. What’s interesting is that even with 120 PSI blasting through them, these multi-part prints held together and sounded amazing.

[AeroKoi] does demonstrate there was a learning curve to climb before he had a good whistle design, and shows you what features worked best. He shared two successes on Thingiverse: A 6-Chime whistle from the Sante Fe Railroad, and a Northern Pacific 5-chime whistle, both 4″ in diameter and printed in vertically sectioned parts. The Northern Pacific is not to be confused with the totally different Union Pacific Railroad, whose famous “Big Boy” also had a whistle feature in the video — though evidently he’s not as happy with it, since he did not share the design.

Those are all North American designs, but there’s no reason this technique wouldn’t work to replicate a more European sound; one of his early experiments was kind of going in that direction already. Of course if you want a perfect replica, the old ways are the best ways: cast brass and live steam. We’ve had a few articles about train whistles in the past, one of which was a doorbell. 

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A hexagonal brass enclosure surrounds an aluminium fan with three blades. The fan has an integrated outer rim with a series of small holes around the rim.

Building A Rim-Driven Jet Engine

Rim-driven thrusters turn the normal propeller-motor arrangement inside out; rather than mounting the motor at the center of the propeller, they use a large hollow motor, with the blades attached to the inside of the rotor. They’re mostly used in ship propellers, though there have been some suggestions to use them in electric aircraft. [Integza], always looking for new and unusual ways to create propulsion, took this idea and made it into a jet engine.

Rather than using an electric motor, the fan in this design is propelled by miniature rocket nozzles along the edge. The fan levitates on a layer of high-pressure gas between the fan rim and the housing. To prevent too much pressurized gas from escaping, the fan and housing needed to fit together closely, but with minimal friction. A prototype made out of acrylic and resin and powered by compressed air proved that the idea worked, but [Integza] wanted to make to this a combustion-powered engine.

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