Understand the Engineering Behind the Impossible Yin Yang Gears

Art & Sculpture Craft & Design Woodworking Workshop
Understand the Engineering Behind the Impossible Yin Yang Gears

While searching through the internet, you may have seen an animation of the Yin Yang symbol moving as a set of gears. Most likely, you moved on and didn’t think about it much more, but prolific woodworker Ronald Walters of the “Ron’s Stuff” YouTube channel decided to instead make his own real-life version of it.

His build is made out of Baltic birch plywood, tempered hardboard, and MDF. It’s painted black, white, and green, and, as seen in the video below, is quite mesmerizing to watch:

YouTube player

The gears were all cut out on a scroll saw (no CNC), and the patterns were developed using Matthias Wandel’s gear generator program. Complete, these gears work together to both spin the outer gear teeth, as well as the inner black and white gears. A motor turns a ring gear on the outside to drive both the outer teeth as well as the white gear, which then drives the black gear.

Although it appears very complicated, the concept is pretty approachable once you understand what it going on. On the other hand, the difference between understanding something, and actually building a high-quality replica of what’s in your head are two different things. Unlike some people (myself definitely included at times) Walters didn’t just get something sort of working and release it to the world. Instead he painted everything nicely, and even sped up the gearing from 3RPM to 6RPM to make it more or less match the actual animation.

This kind of thing does, however, take some time. According to Walters:

I started playing around with this Nov 2015. With a lot of these projects I work on them when I get tired of working on something else. I started editing the video Dec 2015 and completed the project July 2016. Posted the video Nov 2016.

He adds that it took him:

6 or 7 months on and off. Probably 2 weeks actual time. No plans, just played with the gear template generator to come up with the combinations. My original choice of gear motors was too slow. I had to double the speed to match the animation speed and keep it visually interesting.

Walters built his first mechanical clock in 2011, 6 years after he retired (he instead was much more active in building and flying remote controlled airplanes). Since then, he has made many interesting wooden projects, and amazingly the only mistake he made on this one was a very minor defect on the build’s non-visible spacer. As he recounts it:

The only thing that went wrong was when I was planing the tempered hardboard for the spacer. The double sided tape decided to let go and I ruined the spacer. I only had a small piece of that hardboard left and it was just a fraction too small. That’s why there is a small flat spot on the edge of the spacer but since it would not be visible I went ahead and used it anyway.

Just because you have a slightly damaged but hidden part, it may not be a reject. The main lesson here is to come back and finish/perfect your projects. I, and probably many of the people reading this, tend to start something, get distracted, and never go back to it. Or I just finish something to the point where it nominally works, but isn’t painted or running at an optimal speed.

Walters, a retired mechanical engineer also added that:

I thought it was an interesting project. It is easy to get something to work in a computer animation which would be difficult or impossible to have work in real life. The optical impression is the gears are turning into each other, contrary to what would be mechanically possible. So I had to figure out how to stack the gear sets.

So for all the working mechanical engineers (and really anyone) reading this, be sure not to lose that creative spark that hopefully pushed you in the direction of your career in the first place. Perhaps some day you’ll have time to work on all the weird and interesting designs that have been floating around in your head for the last “X” number of years!

For another interesting “Ron’s Stuff” project, be sure to check out this reciprocating rack and pinion gear set that we featured in April 2016.

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Jeremy is an engineer with 10 years experience at his full-time profession, and has a BSME from Clemson University. Outside of work he’s an avid maker and experimenter, building anything that comes into his mind!

View more articles by Jeremy S Cook


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