Unique Planetary Gearbox can be Custom Printed for Steppers

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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Using LTSpice to Measure Total Harmonic Distortion

Audiophiles spend a lot of time and effort worrying about audio specs like Total Harmonic Distortion (THD). Makes sense, because THD affects the quality of audio reproduction. However, THD can also affect interference from radio signals and even losses in power transfer systems. A simplified definition is the THD is the ratio of the sum of the power of all harmonic frequencies to the power of the fundamental frequency.

If a circuit produced a perfect sine wave, there would be no harmonics. There are many ways to measure THD in practice, but [Michael Jackson] has an interesting video showing how he easily visualizes THD using LTSpice. Assuming you already have the system in question in LTSpice (or you could use another simulation tool, if you prefer) it is fairly straightforward.

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Retrotechtacular: Building Hammond Organ Tones

Here’s a short film made by the Hammond Organ Company with the intent to educate and persuade potential consumers. Right away we are assured that Hammond organs are the cream of the crop for two simple reasons: the tone generator that gives them that unique Hammond sound, and the great care taken at every step of their construction.

Hammond organs have ninety-one individual electromagnetic tone wheel assemblies. Each of these generate a specific frequency based on the waviness of a spinning disk’s edge and the speed at which it is rotated in front of an electromagnet. By using the drawbars to stack up harmonics, an organist can build lush walls of sound.

No cost is spared in Hammond’s tireless pursuit of excellence. All transformers are wound in-house and then sealed in wax to make them impervious to moisture. Each tone wheel is cut to exacting tolerances, cross-checked, and verified by an audio specialist. The assembly and fine tuning of the tone generators is so carefully performed that Hammond alleges they’ll never need tuning again.

This level of attention isn’t limited to the guts of the instrument. No, the cabinetry department is just as meticulous. Only the highest-quality lumber is carefully dried, cut, sanded, and lacquered by hand, then rubbed to a high shine. Before it leaves the shop, every Hammond organ is subject to rigorous inspection and a performance test in a soundproofed room.

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AXiS-49 teardown


We touched on harmonic table MIDI controllers when [aris] was building one. [Ken Rushton] has one of C-Thru’s commercial keypads, the AXiS-49, and disassembled the device to show how it works. A PIC18F2450 microcontroller provides the USB interface and is connected to a dsPIC33FJ128GP310 digital signal controller which decodes the keypresses. The membrane buttons are made with two concentric graphite disks that touch gold contacts. The microcontroller measures the time between the two points contacting to determine the button velocity. monome button clones also use circular contact pads, but cannot calculate velocity because they only have one element.

[via Matrixsynth]

Harmonic keyboard controller


[aris] is continuing work on his harmonic table keyboard midi controller. Instead of the traditional linear keyboard layout, keys are laid out in a hexagonal pattern. This is the same idea as the C-Thru AXiS, which you can find a video demo of here. Along the left edge is a row of buttons to transpose the layout up or down. Switches for octave up and down along with a generic slider are also included. The final controller will include a 16×2 LCD character display. The core of the controller is MIDIBox, and he’s using the SDK to write the custom C code. Embedded below is the first test with just four buttons wired.

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