Harmonic Drive Uses Compliant Mechanism To Slim Down

[Levi Janssen] has a secret: he doesn’t like harmonic drives. But rather than abandon the torque-amplifying transmission completely, he decided to see about improving them using 3D-printed compliant mechanisms.

For the uninitiated, harmonic drives, also known as strain-wave gears, are a compact, high-torque gearbox that has become popular with “robotic dog” makers and other roboticists. The idea is to have a rigid, internally-toothed outer ring nested around an externally-toothed, flexible cup. A wave generator rotates within the inside cup, stretching it so that it meshes with the outer ring. The two gears differ by only a couple of teeth, meaning that very high gear ratios can be achieved, which makes them great for the joints of robot legs.

[Levi]’s problem with the harmonic drive is that due to the depth of the flexible spline cup, compactness is not among its virtues. His idea is to couple the flex spline to the output of the drive through a flat spring, one that allows flexion as the wave generator rotates but transmits torque efficiently. The entire prototype is 3D-printed, except for the wave generator bearings and stepper motor, and put to the test.

As the video below shows after the excellent introduction to harmonic drives, the concept works, but it’s not without its limitations. Even lightly loaded, the drive made some unpleasant crunching sounds as the PLA springs gave out. We could easily see that being replaced with, say, a steel spring, either machined or cut on a water-jet machine. That might solve the most obvious problem and make [Levi]’s dream of a compact harmonic drive a reality. Of course, we have seen pretty compact strain-wave gears before.

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The Vibrating Reed Inverter: Possibly The Simplest Inverter You Can Make

Those of us who work on the road have a constant dread of being stuck somewhere without power, facing a race between a publication deadline and a fast-failing laptop battery. We’re extremely fortunate then to live in an age in which a cheap, lightweight, and efficient solid-state switch-mode inverter can give us mains power from a car cigarette lighter socket and save the day. Before these inverters came much heavier devices whose transistors switched at the 50Hz line speed, and before them came electromechanical devices such as the rotary converter or the vibrating reed inverter. It’s this last type that [Robert Murray-Smith] has taken a look at, making what he positions as the simplest inverter that it’s possible.

If you’ve ever played with relays, you’ll probably be aware that a relay can be wired as a buzzer, and it’s this property that a vibrating reed inverter harnesses. He takes an octal relay and wires it up with a small mains transformer for an immediate and very cheap inverter. It’s not perfect, as he points out the frequency isn’t right. The relay will eventually wear out unless the arcing problem is improved with the addition of a capacitor. But it does make a rough and ready inverter if you find yourself in a MacGyver-style tight spot with only your junk box for salvation.

If inverters pique your interest, it might benefit you to know how they work.

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Ask Hackaday: How Do You Prepare?

Last month, large parts of the southern United States experienced their coldest temperatures since the 1899 Blizzard. Some of us set new all-time lows, and I was right in the middle of the middle of it here in Southwestern Oklahoma. Since many houses in Texas and Oklahoma are heated with electricity, the power grids struggled to keep up with the demand. Cities in Oklahoma experienced some short-term rolling blackouts and large patches of the Texas grid were without power for several days. No juice, no heat.

In places where the power was out for an extended period of time, the water supply was potentially contaminated, and a boil order was in effect. Of course, this only works when the gas and power are on. In some places, the store shelves were empty, a result of panic buying combined with perishables spoiling without the power to keep them cold. For some, food and drinkable water was temporarily hard to come by.

There have been other problems, too. Houses in the south aren’t built for the extreme cold, and many have experienced frozen pipes, temporarily shutting off their water supply. In some cases, those frozen pipes break open, flooding the house once the water starts flowing again. For instance, here’s an eye-witness account of the carnage from The 8-bit Guy, who lives at ground zero in the DFW area.
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Trouble With The Texas Power Grid As Cold Weather Boosts Demand, Knocks Out Generators

It comes as something of a shock that residents of the Lone Star State are suffering from rolling power blackouts in the face of an unusually severe winter. First off, winter in Texas? Second, isn’t it the summer heat waves that cause the rolling blackouts in that region?

Were you to mention Texas to a European, they’d maybe think of cowboys, oil, the hit TV show Dallas, and if they were European Hackaday readers, probably the semiconductor giant Texas Instruments. The only state of the USA with a secession clause also turns out to to have their own power grid independent of neighboring states.

An accurate and contemporary portrait of a typical Texan, as understood by Europeans. Carol M. Highsmith, Public domain.
An accurate and contemporary portrait of a typical Texan, as understood by Europeans. Carol M. Highsmith, Public domain.

Surely America is a place of such resourcefulness that this would be impossible, we cry as we watch from afar the red squares proliferating across the outage map. It turns out that for once the independent streak that we’re told defines Texas may be its undoing. We’re used to our European countries being tied into the rest of the continental grid, but because the Texan grid stands alone it’s unable to sip power from its neighbours in times of need.

Let’s dive into the mechanics of maintaining an electricity grid, with the unfortunate Texans for the moment standing in as the test subject.


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A Clock From An Electricity Meter

Electric utilities across the world have been transitioning their meters from the induction analog style with a distinctive spinning disc to digital “smart” meters which aren’t as aesthetically pleasing but do have a lot of benefits for utilities and customers alike. For one, meter readers don’t need to visit each meter every month because they are all networked together and can download usage data remotely. For another, it means a lot of analog meters are now available for projects such as this clock from [Monta].

The analog meters worked by passing any electricity used through a small induction motor which spun at a rate proportional to the amount of energy passing through it. This small motor spun a set of dials via gearing in order to keep track of the energy usage in the home or business. To run the clock, [Monta] connected a stepper motor with a custom transmission to those dials for the clock face because it wasn’t possible to spin the induction motor fast enough to drive the dials. An Arduino controls that stepper motor, but can’t simply drive the system in a linear fashion because it needs to skip a large portion of the “minutes” dials every hour. A similar problem arises for the “hours” dials, but a little bit of extra code solves this problem as well.

Once the actual clock is finished, [Monta] put some finishing touches on it such as backlighting in the glass cover and a second motor to spin the induction motor wheel to make the meter look like it’s running. It’s a well-polished build that makes excellent use of some antique hardware, much like one of his other builds we’ve seen which draws its power from a Stirling engine.

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Graphene Generates A Little Power

We never know exactly what to make of university press releases, as we see plenty of them with breathless claims of new batteries or supermaterials, but then we don’t see much else. Sometimes, the claims in the press release don’t hold up in the paper, while other times the claims seem to be impractical for use in real life. We aren’t quite sure what to make of a press release from the University of Arkansas claiming they can draw current from a sheet of freestanding graphene purely from its temperature fluctuations.

The press release seems to claim that this is a breakthrough leading to “clean, limitless power.” But if you look at the actual paper, normal room temperature is causing tiny displacements in the graphene sheet as in Brownian motion. A scanning tunneling microscope with two diodes can detect current flowing even once the system reaches thermal equilibrium. Keep in mind, though, that this in the presence of a bias voltage and we are talking about nanometer-scale displacements and 20 pA of current. You can see a simple video from the university showing a block diagram of the setup.

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Adding Luxury Charging Features To An Entry-Level EV

The Nissan Leaf is the best-selling electric car of all time so far, thanks largely to it being one of the first mass produced all-electric EVs. While getting into the market early was great for Nissan, they haven’t made a lot of upgrades that other EV manufacturers have made and are starting to lose customers as a result. One of those upgrades is charge limiting, which allows different charging rates to be set from within the car. With some CAN bus tinkering, though, this feature can be added to the Leaf.

Limiting the charging rate is useful when charging at unfamiliar or old power outlets which might not handle the default charge rate. In Europe, which has a 240V electrical distribution system, Leafs will draw around 3 kW from a wall outlet which is quite a bit of power. If the outlet looks like it won’t support that much power flow, it’s handy (and more safe) to be able to reduce that charge rate even if it might take longer to fully charge the vehicle. [Daniel Ă–ster]’s modification requires the user to set the charge rate by manipulating the climate control, since the Leaf doesn’t have a comprehensive user interface.

The core of this project is performed over the CAN bus, which is a common communications scheme that is often used in vehicles and is well-documented and easy to take advantage of. Luckily, [Daniel] has made the code available on his GitHub page, so if you’re thinking about trading in a Leaf for something else because of its lack of features it may be time to reconsider.

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