Riven is a motor driven wooden clock aimed at tearing apart traditional horological reduction methods. It is the first clock to use a system of dual stage hypocycloid reducers on a single shared rotation axis. With a design aesthetic inspired by tourbillons, Riven’s name applies also to its forms. For a brief moment at both noon and midnight, every gear, support, hand, and frame will align. An instant later, the forms split apart as each follows its own unique eccentric motion.
Riven's minute hand “floats” around the perimeter of the clock using ultra high pull neodymium magnets. The ring the hand rides on does not move, and the part that does is over 1/4” away from the hand.
There is also a mechanism to help prevent mechanically overloading the motor that drives the clock. It is a combination clutch and fuse that uses magnets. If any of the hypocycloid mechanisms in the clock bind, if they require higher torque than normal, or if somebody decides to stick their finger in the clock, this clutch/fuse mechanism breaks free, temporarily stopping the time, but saving the motor. A few seconds later, the mechanism automatically attempts to reengage to start the clock back up again.
The idea to use hypocycloid reducers as a means of reduction in a wooden clock came about roughly two years prior to the idea of Riven. My first successful implementation of a dual stage hypocycloid reducer was in my Voor Vander clock. Admittedly, the number of pins and lobed gear teeth used to create Voor Vander’s 12:1 reduction was a once in a lifetime lucky guess on my part. I made up some numbers, put them together, and serendipitously happened to stumble upon the exact ratio I needed. I knew I would not be so lucky in coming up with Riven’s geometry, and so I had to take a step back to truly understand how these mechanisms worked.
I spent several hours generating a handful of hypocycloid designs in CAD, testing their reduction ratios by creating 3D animations of the motions each design would produce. I then had to determine from a mathematical standpoint why they moved the way they did. Frustration ensued. I came up with dozens of equation variations, but none of them worked with all my tested designs. After weeks of failure, I was finally successful in generating an equation that described the motion of all the designs I had created and tested. From there, I built a small software program that would iterate through all possible gear tooth combinations and return back only those combinations whose output matched the desired reduction ratio. After that, the design work began.
From a technical achievement standpoint, I could not be happier with Riven’s end result. Its mechanisms and the math behind them proved to be challenging problems, and as such, they gave me an even greater sense of accomplishment when finally solved. I am thrilled to be able to share the mechanisms and the design of this unique clock.
Woodworking plans and more information about Riven are available on my website: www.derekhugger.com
A video of Riven in action is here: http://youtu.be/jve1CgYGeus
If you’d like to learn more about hypocycloid reducers or would like to create your own, check out my tools page: www.derekhugger.com/tools.html