Anti-Lock Brakes For Bike Might Make Rides A Little Safer

February 17, 2019 by Dan Maloney 59 Comments

Crashing one’s bike is a childhood rite of passage, one that can teach valuable lessons in applied physics. Assuming the kid is properly protected and the crash is fairly tame, scrapes and bruises are exchanged for the wisdom to avoid sand and gravel patches, and how to avoid a ballistic dismount by not applying the front brakes harder than or before the rear brakes.

But for many of us, those lessons were learned long ago using a body far more flexible than the version we’re currently in, and the stakes are higher for a bike ride that includes braking mistakes. To help with that, [Tom Stanton] has been working on anti-lock brakes for bicycles, and in the process he’s learned a lot about the physics and engineering of controlled deceleration.

It seems a simple concept – use a sensor to detect when a wheel is slipping due to decreased friction between the tire and the roadway, and release braking force repeatedly through an actuator to allow the driver or rider to maintain control while stopping. But that abstracts away a ton of detail, which [Tom] quickly got bogged down in. With a photosensor on the front wheel and a stepper motor to override brake lever inputs, he was able to modulate the braking force, but not with the responsiveness needed to maintain control. Several iterations later, [Tom] hit on the right combination of sensors, actuators, and algorithms to make a decent bike ABS system. The video below has all the details of the build and testing.

[Tom] admits bike ABS isn’t much of an innovation. We even covered an Arduino-instrumented bike that was to be an ABS testbed a few years back. But it’s still cool to see how much goes into anti-lock systems.

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ABS: Three Plastics In One

December 11, 2018 by Dan Maloney 31 Comments

It would be really hard to go through a typical day in the developed world without running across something made from ABS plastic. It’s literally all over the place, from toothbrush handles to refrigerator interiors to car dashboards to computer keyboards. Many houses are plumbed with pipes extruded from ABS, and it lives in rolls next to millions of 3D-printers, loved and hated by those who use and misuse it. And in the form of LEGO bricks, it lurks on carpets in the dark rooms of children around the world, ready to puncture the bare feet of their parents.

ABS is so ubiquitous that it makes sense to take a look at this material in terms of its chemistry and its properties. As we’ll see, ABS isn’t just a single plastic, but a mixture that takes the best properties of its components to create one of the most versatile plastics in the world.

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The Filament Pelletizer For Fused Granular Fabrication

December 5, 2018 by Brian Benchoff 24 Comments

The ABS and PLA that goes into your 3D printer is sold in two forms. The first, naturally, is filament. The second is plastic granules, the raw material for your filament, and costs an order of magnitude less than the filament itself. For years we’ve been seeing machines that either print directly with plastic granules or are converted into filament with fancy filament-extruding machines. Now we can do it the other way. [Aubrey Woern] and [Joshua Pearce] of Michigan Tech have been working on a polymer pelletizer chopper that takes plastic filament and turns it into pellets.

The system uses a large corded drill motor to drive a Forstner drill bit. Filament is then threaded into the top of this spinning drill bit with the help of a small DC motor and grippy wheel printed out of Ninjaflex. The system works, and the authors of the paper were able to vary the size of the chopped filament by feeding it into the Forstner bit faster or slower.

While turning an expensive product (filament) back into its raw material (pellets) may not seem like a great idea, there have been a significant number of advancements in the state of manufacturing filament on a desktop and printing directly from pellets in recent years. A machine that turns plastic back into its raw state is something that’s needed if you want to experiment with plastic recycling, and this machine is more than capable of chopping up a spool of filament in two hours or so.

Tariff Expansion Set To Hit 3D-Printing Right In The Filament

August 12, 2018 by Dan Maloney 139 Comments

Mere weeks after tariffs were put into place raising the cost of many Chinese-sourced electronics components by 25%, a second round of tariffs is scheduled to begin that will deal yet another blow to hackers. And this time it hits right at the heart of our community: 3D-printing.

A quick scan down the final tariff list posted by the Office of the US Trade Representative doesn’t reveal an obvious cause for concern. In among the hundreds of specific items listed one will not spot “Filaments for additive manufacturing” or anything else that suggests that 3D-printing supplies are being targeted. But hidden in the second list of tariff items, wedged into what looks like a polymer chemist’s shopping list, are a few entries for “Monofilaments with cross-section dimension over 1 mm.” Uh-oh!

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Results Of 3D-Printed Cylinder Head Testing Fail To Surprise

August 9, 2018 by Dan Maloney 68 Comments

It’s the suburbanista’s weekend nightmare: you’re almost done with the weekly chores, taking the last few passes with the lawn mower, when you hear a pop and bang. The cylinder head on your mower just blew, and you’re out of commission. Or are you? You’ve got a 3D printer – couldn’t it save the day?

If this bench test of plastic cylinder heads is any indication, it’s possible – just as long as you’ve only got 40 seconds of mowing left to do. [Project Farm] has been running all sorts of tests on different materials as field-expedient cylinder heads for small gasoline engines, using everything from JB Weld epoxy to a slab of walnut. For this test, two chunky heads were printed, one from ABS, of the thermochromic variety apparently, the other in PLA. The test went pretty much as expected for something made of thermoplastic exposed to burning gasoline at high pressure, although ABS was the clear winner with two 40-second runs. The PLA only lasted half as long before the spark plug threads melted and the plug blew out. A gasket printed from flexible filament was also tested, with predictably awful results.

As bad as all this was, it still shows that 3D-printed parts are surprisingly tough. Each part was able to perform decently under a compression test, showing that they can stand up to pressure as long as there’s no heat. If nothing else, it was a learning experience. And as an aside, the cylinder heads were printed by [Terry] from the RedNeckCanadians YouTube channel. That video is worth a watch, if just for a few tips on making a 3D-printed copy of an object. Continue reading “Results Of 3D-Printed Cylinder Head Testing Fail To Surprise” →

An MRI-Safe 3D Printed Pneumatic Stepper Motor

July 26, 2018 by Tom Nardi 33 Comments

You will no doubt have seen those videos where MRI machines suck up all sorts of metallic objects with hilariously disastrous results. The magnetic field in one of these machines can easily pull in metal objects from across the room, exerting a force of several hundred pounds on any ferrous object unlucky enough to wander too close. As you can probably imagine, designing mechanical devices that can operate in such an intense magnetic field is exceptionally difficult.

But this fully 3D printed pneumatic stepper motor designed by [Foad Sojoodi Farimani] might one day change that. The PneuAct, which he presented at the recent International Conference on Robotics and Automation (ICRA) in Brisbane, Australia, manages to run at up to 850 RPM with full position control using bursts of air rather than electronic pulses. Made entirely of plastic and without any electronic components, the PneuAct can not only operate in intense magnetic fields but also areas with flammable gases where sparks could potentially cause an explosion.

We often say that a design is “fully” 3D printable, even though it might require screws or other bits of hardware. But in the case of the PneuAct, it’s truly all printed. It has to be, or else the whole thing would be ripped apart when it got to close to the MRI machine. Each and every piece of the motor is printed in ABS, and can be used without any additional machining or cleanup. No lubrication is required, and [Foad] mentions that the whole thing is so cheap that it can be disposable. Which is a huge advantage in medical environments where contamination could be a concern.

Design-wise the PneuAct is essentially an expanded version of the 3D printed air motors we’ve seen previously, but it would be fair to say that none has ever been studied so closely before.

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A 3D-Printed Bowl Feeder For Tiny SMD Parts

July 22, 2018 by Dan Maloney 30 Comments

[Andrzej Laczewski] has something big in mind for small parts, specifically SMD resistors and capacitors. He’s not talking much about that project, but from the prototype 3D-printed bowl feeder he built as part of it, we can guess that it’s going to be a pretty cool automation project.

Bowl feeders are common devices in industrial automation, used to take a big pile of parts like nuts and bolts and present them to a process one at a time, often with some sort of orientation step so that all the parts are the right way around. They accomplish this with a vibratory action through two axes, which [Andrzej] accomplishes with the 3D-printed ABS link arms supporting the bowl. The spring moment of the arms acts to twist the bowl slightly when it’s pulled down by a custom-wound electromagnet, such that the parts land in a slightly different place every time the bowl shifts. For the parts on the shallow ramp spiraling up the inside of the bowl, that means a single-file ride to the top. It’s interesting to see how changing the frequency of the signal sent to the coil impacts the feed; [Andrzej] used a function generator to find the sweet spot before settling on a dedicated circuit. Watch it in action below.

We’re really impressed with the engineering that went into this, even if we wonder what the vibration will do to the SMD components. Still, we can’t wait to see this in a finished project – perhaps it’ll be integrated like this Arduino-fied bowl feeder.

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