Wave Drive Made With 3D Printed Parts

June 8, 2025 by Lewin Day 10 Comments

You can get just about any gear reduction you want using conventional gears. But when you need to get a certain reduction in a very small space with minimal to no backlash, you might find a wave drive very useful. [Mishin Machine] shows us how to build one with (mostly) 3D printed components.

The video does a great job of explaining the basics of the design. Right off the bat, we’ll say this one isn’t fully printed—it relies on off-the-shelf steel ball bearings. It’s easy to understand why. When you need strong, smooth-rolling parts, it’s hard to print competitive spheres in plastic at home. Plastic BBs will work too, though, as will various off-the-shelf cylindrical rollers. The rest is mostly 3D printed, so with the right design, you can whip up a wave drive to suit whatever packaging requirements you might have.

Combined with a stepper motor and the right off-the-shelf parts, you can build a high-reduction gearbox that can withstand high torque and should have reasonable longevity despite being assembled with many printed components.

We’ve seen other interesting gear reductions before, too.

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Illustrated scheme of Sam Ben Yaakovs concept

Leakage Control For Coupled Coils

June 5, 2025 by Heidi Ulrich 3 Comments

Think of a circuit model that lets you move magnetic leakage around like sliders on a synth, without changing the external behavior of your coupled inductors. [Sam Ben-Yaakov] walks you through just that in his video ‘Versatile Coupled Inductor Circuit Model and Examples of Its Use’.

The core idea is as follows. Coupled inductors can be modeled in dozens of ways, but this one adds a twist: a tunable parameter 𝑥 between k and ₁ (where k is the coupling coefficient). This fourth degree of freedom doesn’t change L_₁, L_₂ or mutual inductance M (they remain invariant) but it lets you shuffle leakage where you want it, giving practical flexibility in designing or simulating transformers, converters, or filters with asymmetric behavior.

If you need leakage on one side only, set 𝑥=k. Prefer symmetrical split? Set 𝑥=1. It’s like parametric EQ, but magnetic. And: the maths holds up. As [Sam Ben-Yaakov] derives and confirms that for any 𝑥 in the range, external characteristics remain identical.

It’s especially useful when testing edge cases, or explaining inductive quirks that don’t behave quite like ideal transformers should. A good model to stash in your toolbox.

As we’ve seen previously, [Sam Ben-Yaakov] is at home when it comes to concepts that need tinkering, trial and error, and a dash of visuals to convey. Continue reading “Leakage Control For Coupled Coils” →

Spin-Casting This Telescope Mirror In Resin Didn’t Go To Plan

June 3, 2025 by Lewin Day 29 Comments

For most of us, mirrors are something we buy instead of build. However, [Unnecessary Automation] wanted to craft mirrors of his own for a custom telescope build. As it turns out, producing optically-useful mirrors is not exactly easy.

For the telescope build in question, [Unnecessary Automation] needed a concave mirror. Trying to get that sort of shape with glass can be difficult. However, there’s such a thing as a “liquid mirror” where spinning fluid forms into a parabolic-like shape. Thus came the idea to spin liquid resin during curing to try and create a mirror with the right shape.

That didn’t quite work, but it inspired a more advanced setup where a spinning bowl and dense glycerine fluid was used to craft a silicone mold with a convex shape. This could then be used to produce a resin-based mirror in a relatively stationary fashion. From there, it was just necessary to plate a shiny metal layer on to the final part to create the mirror effect. Unfortunately, the end result was too messy to use as a viable telescope mirror, but we learn a lot about what didn’t work along the way.

The video is a great journey of trial and error. Sometimes, figuring out how to do something is the fun part of a project, even if you don’t always succeed. If you’ve got ideas on how to successfully spin cast a quality mirror, drop them in the comments below. We’ve seen others explore mirror making techniques before, too.

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Wire-frame image of gearbox, setup as a differential

Roller Gearbox Allows For New Angles In Robotics

May 22, 2025 by Ian Bos 17 Comments

DIY mechatronics always has some unique challenges when relying on simple tools. 3D printing enables some great abilities but high precision gearboxes are still a difficult problem for many. Answering this problem, [Sergei Mishin] has developed a very interesting gearbox solution based on a research paper looking into simple rollers instead of traditional gears. The unique attributes of the design come from the ability to have a compact angled gearbox similar to a bevel gearbox.

Multiple rollers rest on a simple shaft allowing each roller to have independent rotation. This is important because having a circular crown gear for angled transmission creates different rotation speeds. In [Sergei]’s testing, he found that his example gearbox could withstand 9 Nm with the actual adapter breaking before the gearbox showing decent strength.

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Series of purple and red mechanisms are stretched from left to right. Almost like arrows pointing right.

Compliant Mechanism Shrinks Instead Of Stretching

May 16, 2025 by Ian Bos 16 Comments

Intuitively, you think that everything that you stretch will pull back, but you wouldn’t expect a couple of pieces of plastic to win. Yet, researchers over at [AMOLF] have figured out a way to make a mechanism that will eventually shrink once you pull it enough.

Named “Counter-snapping instabilities”, the mechanism is made out of the main sub-components that act together to stretch a certain amount until a threshold is met. Then the units work together and contract until they’re shorter than their initial length. This is possible by using compliant joints that make up each of the units. We’ve seen a similar concept in robotics.

Potentially this may be used as a unidirectional actuator, allowing movement inch by inch. In addition, one application mentioned may be somewhat surprising: damping. If a structure or body is oscillating through a positive feedback loop it may continue till it becomes uncontrollable. If these units are used, after a certain threshold of oscillation the units will lock and retract, therefore stopping further escalation.

Made possible by the wonders of compliant mechanics, these shrinking instabilities show a clever solution to some potential niche applications. If you want to explore the exciting world of compliance further, don’t be scared to check out this easy to print blaster design!

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Five Oddest Op Amp Applications

May 6, 2025 by Al Williams 25 Comments

You think of op amps as amplifiers because, no kidding, it is right in the name. But just like some people say, “you could do that with a 555,” [Doctor Volt] might say, “you can do that with an op amp.” In a recent video, you can see below, he looks at simulations and breadboards for five applications that aren’t traditional amplifiers.

Of course, you can split hairs. A comparator is sort of an amplifier with some very specific parameters, but it isn’t an amplifier in the classic sense.

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Round Displays Make Neat VU Meters

May 5, 2025 by Lewin Day 11 Comments

You can still get moving-needle meters off the shelf if you desire that old school look in one of you projects. However, if you want a more flexible and modern solution, you could use round displays to simulate the same thing, as [mircemk] demonstrates.

At the heart of the build is an ESP32 microcontroller, chosen for its fast clock rate and overall performance. This is key when drawing graphics to a display, as it allows for fast updates and smooth movement — something that can be difficult to achieve on lesser silicon. [mircemk] has the ESP32 reading an audio input and driving a pair of GC9A01 round displays, which are the perfect form factor for aping the looks of a classic round VU meter. The project write-up goes into detail on the code required to simulate the behavior of a real meter, from drawing the graphics to emulating realistic needle movements, including variable sweep rates and damping.

The cool thing about using a screen like this is the flexibility. You can change the dials to a different look — or to an entirely different kind of readout — at will. We’ve seen some of [mircemk]’s projects before, too, like this capable seismometer. Video after the break.

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