Shape Shifting Structures Work With Magnets

December 15, 2018 by Brian McEvoy 12 Comments

In The Dark Knight, Lucius Fox shows Bruce Wayne a neat bit of memory weave fabric. In its resting state, it is a light, flexible material, but when an electrical current is applied, it pops into a pre-programmed shape. That shape could be a tent or a bat-themed paraglider. Science has not caught up to Hollywood in this regard, but the concept has been demonstrated in a material which increases its rigidity up to 318% within one second when placed in a magnetic field. Those numbers do not mean a lot by themselves, but increasing rigidity in a reversible, non-chemical way is noteworthy.

The high-level explanation is that hollow tubes are 3D printed and filled with magnetorheological fluid which becomes more viscous in the presence of a magnet because the ferrous suspended particles bunch up to form chains instead of sliding over one another. Imagine a bike tire filled with gel, and when you need a little extra traction the tire becomes softer, but when you are cruising on a paved trail, the tire becomes as hard as a train wheel to reduce friction. That could be darn handy in more places than building a fast bike.

Imploding Tiny 3D Prints

December 15, 2018 by Al Williams 10 Comments

If you think about 3D printing, the ultimate goal would be to lay down specific atoms or molecule and build anything. Despite a few lab demonstrations at that scale, generally, it is easier to print in the macro scale than the micro. While it won’t get down to the molecule level, implosion fabrication is a new technique researchers hope will allow you to print large things and then shrink them. The paper describing the process appeared in Science. If you don’t want to pay your way through the paywall, you can read a summary on NewScientist or C&EN. Or you can scour the usual sources.

The team at MIT uses the same material that is found in disposable diapers. A laser traces patterns and the light reacts to a chemical implanted in the diaper material (sodium polyacrylate). That material can swell to many times its normal size which is why it is used in diapers. In this case, though, the material is swollen first and then reduced back to normal size.

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Lessons Learned From A 1-Day RTL-SDR Enclosure Project

December 14, 2018 by Donald Papp 9 Comments

[ByTechLab] needed an enclosure for his R820T2 based RTL-SDR, which sports an SMA connector. Resolving to design and 3D print one in less than a day, he learned a few things about practical design for 3D printing and shared them online along with his CAD files.

The RTL-SDR is a family of economical software defined radio receivers, and [ByTechLab]’s’ enclosure (CAD files available on GrabCAD and STL on Thingiverse) is specific to his model. However, the lessons he learned are applicable to enclosure design in general, and a few of them specifically apply to 3D printing.

He started by making a basic model of the PCB and being sure to include all large components. With that, he could model the right voids inside the enclosure to ensure a minimum of wasted space. The PCB lacks any sort of mounting holes, so the model was also useful to choose where to place some tabs to hold the PCB in place. That took care of the enclosure design, but it also pays to be mindful of the manufacturing method so as to play to its strengths. For FDM 3D printing, that means most curved shapes and rounded edges are trivial. It also means that the biggest favor you can do yourself is to design parts so that they can be printed in a stable orientation without any supports.

This may be nothing that an experienced 3D printer and modeler doesn’t already know, but everyone is a novice at some point and learning from others’ experiences can be a real timesaver. For the more experienced, we covered a somewhat more in-depth guide to practical 3D printed enclosure design.

[ByTechLab]’s desire for a custom enclosure was partly because RTL-SDR devices come in many shapes and sizes, as you can see in this review of 19 different units (of which only 14 actually worked.)

True Transparent Parts From A Desktop 3D Printer

December 11, 2018 by Tom Nardi 14 Comments

We’re no strangers to seeing translucent 3D printed parts: if you print in a clear filament with thin enough walls you can sorta see through the resulting parts. It’s not perfect, but if you’re trying to make a lamp shade or decorative object, it’s good enough. You certainly couldn’t print anything practical like viewing windows or lenses, leaving “clear” 3D printing as more of a novelty than a practical process.

But after months of refining his process, [Tomer Glick] has finally put together his guide for creating transparent prints on a standard desktop FDM machine. It doesn’t even require any special filament, he says it will work on PLA, ABS, or PETG, though for the purposes of this demonstration he’s using the new Prusament ABS. The process requires some specific print settings and some post processing, but the results he’s achieved are well worth jumping though a few hoops.

According to [Tomer] the secret is in the print settings. Essentially, you want the printer to push the layers together far closer than normal, in combination with using a high hotend temperature and 100% infill. The end result (hopefully) is the plastic being laid down by the printer is completely fused with the preceding one, making a print that is more of a literal solid object than we’re used to seeing with FDM printing. In fact, you could argue these settings generate internal structures that are nearly the polar opposite of what you’d see on a normal print.

The downside with these unusual print settings is that the outside of the print is exceptionally rough and ugly (as you might expect when forcing as much plastic together as possible). To expose the clear internals, you’ll need to knock the outsides down with some fairly intense sanding. [Tomer] says he starts with 600 and works his way up to 4000, and even mentions that when you get up to the real high grits you might as well use a piece of cardboard to sand the print because that’s about how rough the sandpaper would be anyway.

[Tomer] goes on to demonstrate a printed laser lens, and even shows how you can recreate the effect of laser-engraved acrylic by intentionally putting voids inside the print in whatever shape you like. It’s a really awesome effect and honestly something we would never have believed came off a standard desktop 3D printer.

In the past we’ve seen specialized filament deliver some fairly translucent parts, but those results still weren’t as good as what [Tomer] is getting with standard filament. We’re very interested in seeing more of this process, and are excited to see what kind of applications hackers can come up with.

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Better Mechanical Keyboards Through 3D Printing

December 7, 2018 by Brian Benchoff 14 Comments

You’re not cool unless you have a mechanical keyboard. No, you won’t be able to tell if your coworkers don’t like it, because you won’t be able to hear their complaining over the sound of your clack-clack-clacking. You can even go all-in with switch modifications, o-rings, and new springs, or you could use your 3D printer to modify the touch of your wonderful Cherry MX switches. That’s what a few researchers did, and the results are promising.

The ‘problem’ this research is attempting to solve is bottoming out on Cherry MX keyswitches. If you’re bottoming out, you’re doing it wrong, but nevertheless, you can get a publication out of solving repetitive strain injury. This was done by modeling the bottom housing of a Cherry MX switch by printing most of it in nylon on a Stratasys Objet 350 polyjet printer, with a tiny bit of of the housing printed with a polymer with a hardness of Shore 40. No, Shore A, Shore B, or Shore 00 was not specified, but hey, it’s just a conference paper.

The experimental test for this keyswitch was dropping a 150 gram weight from 125 mm onto the keyswitch, with a force sensitive resistor underneath the switch, connected to an Arduino. Data was logged, filtered, and fitted in Excel to create a plot of the force on dampened, rigid, and commercial switch housings. Results from ANOVA were p > 0.05 (p=0.12).

Despite the lack of significant results, there is something here. The Objet is one of the few printers that can do multimaterial printing with the resolution needed to replicate an injection molded part. There is a trend to the data, and printing squishy parts into a keyswitch should improve typing feel. There will be more work on this, but in the meantime we’re hopeful some other experimenters will pick up this train of research.

Etch-a-Sketch 3D Printed With Cell Phone

December 3, 2018 by Al Williams 13 Comments

Most of us have fond memories of the Etch-a-Sketch from childhood. [Potent Printables] wanted to update the designs so he 3D printed an XY carriage for a stylus that works with a cell phone drawing program. You can see the video below and the 3D model details on Thingiverse.

The design is fun all by itself, but it also gave us a few ideas. For one thing, if you motorized it you could make some pretty clever drawing toys. But there could be a more practical use, too.

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3D Printed Brushed Motor Is Easy To Visualize

December 1, 2018 by Al Williams 5 Comments

A motor — or a generator — requires some normal magnets and some electromagnets. The usual arrangement is to have a brushed commutator that both powers the electromagnets and switches their polarity as the motor spins. Permanent magnets don’t rotate and attract or repel the electromagnets as they swing by. That can be a little hard to visualize, but if you 3D Print [Miller’s Planet’s] working model — or just watch the video below — you can see how it all works.

We imagine the hardest part of this is winding the large electromagnets. Getting the axle — a nail — centered is hard too, but from the video, it looks like it isn’t that critical. There was a problem with the link to the 3D model files, but it looks like this one works.

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