reduction

7 Articles

Harmonic Drive Uses Compliant Mechanism To Slim Down

April 7, 2021 by 15 Comments

[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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Simple Demo Shows The Potential Of Magnetic Gears

April 13, 2020 by 27 Comments

We’ve probably all used gears in our projects at one time or another, and even if we’re not familiar with the engineering details, the principles of transmitting torque through meshed teeth are pretty easy to understand. Magnetic gears, though, are a little less intuitive, which is why we appreciated stumbling upon this magnetic gear drivetrain demonstration project.

[William Fraser]’s demo may be simple, but it’s a great introduction to magnetic gearing. The stator is a block of wood with twelve bolts to act as pole pieces, closely spaced in a circle around a shaft. Both ends of the shaft have rotors, one with eleven pairs of neodymium magnets arranged in a circle with alternating polarity, and a pinion on the other side of the stator with a single pair of magnets. When the pinion is spun, the magnetic flux across the pole pieces forces the rotor to revolve in the opposite direction at a 12:1 ratio.

Watching the video below, it would be easy to assume such an arrangement would only work for low torque applications, but [William] demonstrated that the system could take a significant load before clutching out. That could even be a feature for some applications. We’ve got an “Ask Hackaday” article on magnetic gears if you want to dive a little deeper and see what these interesting mechanisms are good for.

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Cheap PSoC Enables Electrochemistry Research

August 4, 2018 by 8 Comments

You may think electrochemistry sounds like an esoteric field where lab-coated scientists labor away over sophisticated instruments and publish papers that only other electrochemists could love. And you’d be right, but only partially, because electrochemistry touches almost everything in modern life. For proof of that look no further than your nearest pocket, assuming that’s where you keep your smartphone and the electrochemical cell that powers it.

Electrochemistry is the study of the electrical properties of chemical reactions and does indeed need sophisticated instrumentation. That doesn’t mean the instruments have to break the grant budget, though, as [Kyle Lopin] shows with this dead-simple potentiostat built with one chip and one capacitor. A potentiostat controls the voltage on an electrode in an electrochemical cell. Such cells have three electrodes — a working electrode, a reference electrode, and a counter electrode. The flow of electrons between these electrodes and through the solutions under study reveal important properties about the reduction and oxidation states of the reaction. Rather than connect his cell to an expensive potentiostat, [Kyle] used a Cypress programmable system-on-chip development board to do everything. All that’s needed is to plug the PSoC into a USB port for programming, connect the electrodes to GPIO pins, and optionally add a 100 nF capacitor to improve the onboard DAC’s accuracy. The video below covers the whole process, albeit with a barely audible voiceover.

Still not sure about electrochemistry? Check out this 2018 Hackaday Prize entry that uses the electrochemistry of life to bring cell phones back to life.

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Have Chainsaw, Will Travel

May 2, 2017 by 31 Comments

What’s the worst thing that could happen if you strapped a chainsaw motor to a tricycle? Turns out the worst that happened to [ThisDustin] and his friends is that it turned out hilariously awesome.

This aptly-named ‘chainsawtrike’ isn’t much in the way of comfort, so a pair of foot pegs had to be welded onto the front forks, along with a mount for the chainsaw motor. The rear axle had to be replaced with 5/8″ keyed stock, trimmed to fit the trike wheel and secured with keyed hubs. [ThisDustin] and crew also needed an intermediate sprocket to act as a reduction gear.

After a test that saw the chain jump off the sprockets and working out a few kinks — like the ability to turn — the chainsawtrike  can haul around its rider at a pretty decent clip. Check out the video of it in action after the break.

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Customize Your Ratios With A 3D-Printed Gearbox

April 12, 2017 by 13 Comments

Small DC motors are easy to find — you can harvest dozens from old printers and copiers. You might even get a few with decent gearboxes too. But will you get exactly the motor with exactly the gearing your project needs? Unlikely, but you can always just print a gearbox to get exactly what you need.

There’s nothing fancy about [fortzero]’s gearboxes. The motors are junk bin specials, and the gears are all simple spur gears 3D-printed from PLA. There are four gears in the train, each with a 2:1 reduction, giving a 16:1 overall ratio. The gears ride on brass shafts that are press-fit into the housing, and there’s not a bearing in sight — just a few washers to keep the gears spaced apart and plenty of grease. Despite the simplicity, the gearboxes turned out to be pretty capable, lifting a 3.5 kg load. The design files are available and should make it easy for you to get just the ratio you want for the motor you have.

Of course more complicated gearboxes are possible with a 3D printer, including a split-harmonic planetary gear, or a strain wave gear using a timing belt. No 3D printer? No problem! Just build a LEGO gearbox.

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Unique Planetary Gearbox Can Be Custom Printed For Steppers

March 2, 2017 by 44 Comments

Stepper motors are a staple in all sorts of projects, but it’s often the case that a gearbox is needed, especially for applications like the linear drives in CNC machines and 3D printers. In those mechanisms, a high-torque, low backlash gearbox might be just the thing, and a 3D printable split planetary harmonic drive for the popular NEMA 17 motors would be even better.

Right up front, we’ll say that we’re skeptical that any plastic gearbox can stay as backlash free as [SirekSBurom] claims his creation is. But we can see the benefits of the design, and it has some nice features. First off, of course, is that it’s entirely 3D printed, except for a few screws. That it mates perfectly with a NEMA 17 motor is a really nice feature, too, and with the design up on Thingiverse it shouldn’t be too tough to scale it up and down accordingly. The videos below show you the theory: the stepper drives a sun gear with two planet gears orbiting, each of which engages a fixed ring of 56 teeth, and an output ring of 58 teeth. Each revolution of the planets around the fixed ring rotates the output ring by one tooth, leading to almost 100:1 reduction.

We think the ‘harmonic’ designation on this gearbox is a little of a misnomer, since the defining feature of a harmonic drive seems to be the periodic deformation of a flex spline, as we saw in this 3D-printed strain wave gear. But we see the resemblance to a harmonic drive, and we’ll admit this beastie is a little hard to hang a name tag on. Whatever you call it, it’s pretty cool and could be a handy tool for all kinds of builds.

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Liquid Metal Changes Shape To Tune Antenna

August 31, 2015 by 39 Comments

Antennas can range from a few squiggles on a PCB to a gigantic Yagi on a tower. The basic laws of physics must be obeyed, though, and whatever form the antenna takes it all boils down to a conductor whose length resonates at a specific frequency. What works at one frequency is suboptimal at another, so an adjustable antenna would be a key component of a multi-band device. And a shape-shifting liquid metal antenna is just plain cool.

The first thing that pops into our head when we think of liquid metal is a silvery blob of mercury skittering inside the glass vial salvaged out of an old thermostat. The second image is a stern talking-to by the local HazMat team, so it’s probably best that North Carolina State University researchers [Michael Dickey] and [Jacob Adams] opted for gallium alloys for their experiments. Liquid at room temperature, these alloys have the useful property of oxidizing on contact with air and forming a skin. This allows the researchers to essentially extrude a conductor of any shape. What’s more, they can electrically manipulate the oxidative state of the metal and thereby the surface tension, allowing the conductor to change length on command. Bingo – an adjustable length antenna.

Radio frequency circuits aren’t the only application for gallium alloys. We’ve already seen liquid metal 3D printing with them. But we need to be careful, since controlling the surface tension of liquid metals might also bring us one step closer to this.