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Hackaday Links: September 25, 2022

Looks like there’s trouble out at L2, where the James Webb Space Telescope suffered a mechanical anomaly back in August. The issue, which was just announced this week, involves only one of the six imaging instruments at the heart of the space observatory, known as MIRI, the Mid-Infrared Instrument. MIRI is the instrument on Webb that needs the coldest temperatures to work correctly, down to six Kelvins — we’ve talked about the cryocooler needed to do this in some detail. The problem has to do with unexpectedly high friction during the rotation of a wheel holding different diffraction gratings. These gratings are rotated into the optical path for different measurements, but apparently the motor started drawing excessive current during its move, and was shut down. NASA says that this only affects one of the four observation modes of MIRI, and the rest of the instruments are just fine at this time. So they’ve got some troubleshooting to do before Webb returns to a full program of scientific observations.

There’s an old saying that, “To err is human, but to really screw things up takes a computer.” But in Russia, to really screw things up it takes a computer and a human with a really poor grasp on just how delicately balanced most infrastructure systems are. The story comes from Moscow, where someone allegedly spoofed a massive number of fake orders for taxi rides (story in Russian, Google Translate works pretty well) through the aggregator Yandex.Taxi on the morning of September 1. The taxi drivers all dutifully converged on the designated spot, but instead of finding their fares, they just found a bunch of other taxis milling about and mucking up traffic. Yandex reports it has already added protection against such attacks to its algorithm, so there’s that at least. It’s all fun and games until someone causes a traffic jam.

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A Line Follower With No Brains

A line follower is a common project for anyone wishing to make a start in robotics, a small wheeled device usually with some kind of optical sensor which allows it to follow a line drawn on the surface over which it runs. In most cases they incorporate a small microcontroller or perhaps an analogue computer which supplies power and steering control, but as the Crayon Car from [Greg Zumwalt] demonstrates, it’s possible to make a line follower without any brains at all.

This seemingly impossible feat is achieved thanks to the line and road surface, it runs on a piece of paper over which the line is drawn with a crayon. The robot has a single straight-line drive wheel at one end and a pair of driven rollers at 90 degrees to each other at the other end, with the magic happening due to the difference in friction between paper and crayon. The robot follows a circular track with no problem, and while we can see it’s not without flaws we doubt it would be possible to make a simpler follower.

Sharp-eyed readers will have noticed that this is not the first line follower we’ve shown you which claims to have no brains, but we’d claim that since the previous machine had an analogue circuit, this one is a more worthy contender to the crown.

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Magnetic Bearings Put The Spin On This Flywheel Battery

[Tom Stanton] is right about one thing: flywheels make excellent playthings. Whether watching a spinning top that never seems to slow down, or feeling the weird forces a gyroscope exerts, spinning things are oddly satisfying. And putting a flywheel to work as a battery makes it even cooler.

Of course, using a flywheel to store energy isn’t even close to being a new concept. But the principles [Tom] demonstrates in the video below, including the advantages of magnetically levitated bearings, are pretty cool to see all in one place. The flywheel itself is just a heavy aluminum disc on a shaft, with a pair of bearings on each side made of stacks of neodymium magnets. An additional low-friction thrust bearing at the end of the shaft keeps the systems suitably constrained, and allows the flywheel to spin for twelve minutes or more.

[Tom]’s next step was to harness some of the flywheel’s angular momentum to make electricity. He built a pair of rotors carrying more magnets, with a stator of custom-wound coils sandwiched between. A full-wave bridge rectifier and a capacitor complete the circuit and allow the flywheel to power a bunch of LEDs or even a small motor. The whole thing is nicely built and looks like a fun desk toy.

This is far from [Tom]’s first flywheel rodeo; his last foray into storing mechanical energy wasn’t terribly successful, but he has succeeded in making flywheels fly, one way or another.

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Cable Mechanism Maths: Designing Against The Capstan Equation

I fell in love with cable driven mechanisms a few years ago and put together some of my first mechanical tentacles to celebrate. But only after playing with them did I start to understand the principles that made them work. Today I want to share one of the most important equations to keep in mind when designing any device that involves cables, the capstan equation. Let some caffeine kick in and stick with me over the next few minutes to get a sense of how it works, how it affects the overall friction in your system, and how you can put it to work for you in special cases.

A Quick Refresher: Push-Pull Cable Driven Mechanisms

But first: just what exactly are cable driven mechanisms? It turns out that this term refers to a huge class of mechanisms, so we’ll limit our scope just to push-pull cable actuation systems.

These are devices where cables are used as actuators. By sending these cables through a flexible conduit, they serve a similar function to the tendons in our body that actuate our fingers. When designing these, we generally assume that the cables are both flexible and do not stretch when put in tension. Continue reading “Cable Mechanism Maths: Designing Against The Capstan Equation”

Anything Becomes A Clock

Clocks are a popular project around here, and with good reason. There’s a ton of options, and there’s always a new take on ways to tell time. Clocks using lasers, words, or even ball bearings are all atypical ways of displaying time, but like a mathematician looking for a general proof of a long-understood idea this clock from [Julldozer] shows us a way to turn any object into a clock.

His build uses AA-powered clock movements that you would find on any typical wall clock, rather than reaching for his go-to solution of an Arduino and a stepper motor. The motors that drive the hands in these movements are extremely low-torque and low-power which is what allows them to last for so long with such a small power source. He uses two of them, one for hours and one for minutes, to which he attaches a custom-built lazy Suzan. The turntable needs to be extremely low-friction so as to avoid a situation where he has to change batteries every day, so after some 3D printing he has two rotating plates which can hold any object in order to tell him the current time.

While he didn’t design a clock from scratch or reinvent any other wheels, the part of this project that shines is the way he was able to utilize such a low-power motor to turn something so much heavier. This could have uses well outside the realm of timekeeping, and reminds us of this 3D-printed gear set from last year’s Hackaday prize.

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Greasing Robot Hands: Variable Friction Makes Robo-Mitts More Like Our Own

Unless you are in the fields of robotics or prosthetics, you likely take for granted the fine motor skills our hands have. Picking up and using a pen is no small feat for a robot which doesn’t have a dedicated pen-grabbing apparatus. Holding a mobile phone with the same gripper is equally daunting, not to mention moving that phone around once it has been grasped. Part of the wonder of our hands is the shape and texture which allows pens and phones to slide around at one moment, and hold fast the next moment. Yale’s Grab Lab has built a gripper which starts to solve that problem by changing the friction of the manipulators.

A spring-loaded set of slats with a low-friction surface allow a held object to move freely, but when more pressure is exerted by the robot, the slats retract and a high-friction surface contacts the object. This is similar to our fingers with their round surfaces. When we brush our hands over something lightly, they graze the surface but when we hold tight, our soft flesh meets the surface of the object and we can hold tightly. The Grab Lab is doing a great job demonstrating the solution and taking steps to more capable robots. All hail Skynet.

We have no shortage of gripper designs to choose from, including pneumatic silicone and one that conforms to an object’s surface, similar to our hands.

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Gecko Feet In Space

Space is a mess, and the sad truth is, we made it that way. Most satellites that have been lofted into Earth orbit didn’t have a plan for retiring them, and those dead hulks, along with the various bits of jetsam in the form of shrouds, fairings, and at least one astronaut’s glove, are becoming a problem.

A mission intended to clean up space junk would be fantastically expensive, but money isn’t the only problem. It turns out that it’s really hard to grab objects in space unless they were specifically designed to be grabbed. Suction cups won’t work in the vacuum of space, not everything up there is ferromagnetic, and mechanical grippers would have to deal with a huge variety of shapes, sizes, and textures.

But now news comes from Stanford University of a dry adhesive based on the same principle a gecko uses to walk up a wall. Gecko feet have microscopic flaps that stick to surfaces because of Van der Waals forces. [Mark Cutkosky] and his team’s adhesive works similarly, adhering to surfaces only when applied in a certain direction. This is an advantage over traditional pressure-sensitive adhesives; the force needed to apply them would cause the object to float away in space. The Stanford grippers have been tested on the “vomit comet” and aboard the ISS.

We can think of tons of terrestrial applications for this adhesive, including the obvious wall-walking robots. The Stanford team also lists landing pads for drones that would let then perch in odd locations, which we find intriguing.

Need to get up to speed on more mundane adhesive? Check out our guide to sticky stuff for the shop.

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