It’s official: [Engineer Bo] wins the internet with a video titled “Finding NEMA 17,” wherein he builds a dynamometer to find the best stepper motor in the popular NEMA 17 frame size.

Like a lot of subjective questions, the only correct answer to which stepper is best is, “It depends,” and [Bo] certainly has that in mind while gathering the data needed to construct torque-speed curves for five samples of NEMA 17 motors using his homebrew dyno. The dyno itself is pretty cool, with a bicycle disc brake to provide drag, a load cell to measure braking force, and an optical encoder to measure the rotation of the motor under test. The selected motors represent a cross-section of what’s commonly available today, some of which appear in big-name 3D printers and other common applications.

[Bo] tested each motor with two different drivers: the TMC2209 silent driver to start with, and because he released the Magic Smoke from those, the higher current TB6600 module. The difference between the two drivers was striking, with lower torque and top speeds for the same settings on each motor using the TB6600, as well as more variability in the data. Motors did better across the board with the TBC6600 at 24 volts, showing improved torque at higher speeds, and slightly higher top speeds. He also tested the effect of microstepping on torque using the TBC6600 and found that using full steps resulted in higher torque across a greater speed range.

At the end of the day, it seems as if these tests say more about the driver than they do about any of the motors tested. Perhaps the lesson here is to match the motor to the driver in light of what the application will be. Regardless, it’s a nice piece of work, and we really appreciate the dyno design to boot — reminds us of a scaled-down version of the one [Jeremey Fielding] demonstrated a few years back.

With few exceptions, power transmission is a field where wobbling is a bad thing. We generally want everything running straight and true, with gears and wheels perfectly perpendicular to their shafts, with everything moving smoothly and evenly. That’s not always the case, though, as this pericyclic gearbox demonstrates.

Although most of the components in [Retsetman] model gearboxes seem familiar enough — it’s mostly just a collection of bevel gears, like you’d see inside a differential — it’s their arrangement that makes everything work. More specifically, it’s the shaft upon which the bevel gears ride, which has a section that is tilted relative to the axis of the shaft. It’s just a couple of degrees, but that small bit of inclination, called mutation, makes the ring gear riding on it wobble as the shaft rotates, allowing it to mesh with one or more ring gears that are perpendicular to the shaft. This engages a few teeth at a time, transferring torque from one gear to another. It’s easier to visualize than it is to explain, so check out the video below.

Gearboxes like these have a lot of interesting properties, with the main one being gear ratio. [Retsetman] achieved a 400:1 ratio with just 3D printed parts, which of course impose their own limitations. But he was still able to apply some pretty serious torque. The arrangement is not without its drawbacks, of course, with the wobbling bits naturally causing unwelcome vibrations. That can be mitigated to some degree using multiple rotatins elements that offset each other, but that only seems to reduce vibration, not eliminate it.

[Retsetman] is no stranger to interesting gearboxes, of course, with his toothless magnetic gearboxes coming to mind. And this isn’t the only time we’ve seen gearboxes go all wobbly, either.

Thanks to [Keith Olson] for the tip.