“It’s a solution looking for a problem, and hopefully you can find the problem.”
The solution that puzzle inventor Oskar van Deventer has come up with is a fist-sized 11,373,076:1 gearbox. That’s no typo — to get the output to rotate only once would require over 11 million rotations of the input shaft. Why? He’s not sure; he wants that to be your job.
With the normal (“spur”) gears we all think of for basic gears, changing the speed of a shaft is space intensive. For example, to change the speed by 5x one gear must be five times the diameter of the other. This is okay for small reductions but is cumbersome for larger ratios. For this reason, multiple stages are often implemented.
The typical way of achieving high gear reductions is to use either a planetary gearset (one or two stages of which are in most electric drills) or a worm gear (as in a sewing machine).
Headed in a different direction, Van Deventer has a new type of gear he calls “grinder gears” that comprise an inner gear with one fewer tooth than the outer gear, causing it to wobble its way through the rotation. For the engineers, it’s a variation of a cycloidal drive. The secret is that these gears allow a geardown based on the amount of teeth instead of their physical size differences.
What’s Inside the Gearbox?
First off of the crank is a dual-stage planetary; this powers a dual-stage grinder. The grinders move in opposite directions, but are one tooth off of each other themselves (27 vs 26 teeth, with the inner gears 26 and 25 teeth respectively). What the yellow gear does to the green gear is almost completely undone by the orange gear (but not quite) leaving the orange gear to vary by infinitesimal amounts relative to the yellow. Adding up all the gear types and stages yields the 11,373,076:1 ratio.
The inventor has not come up with any, so, to get started let us look at what it would be tempting but unsuitable for.
Precision: One might think that because the output moves so gradually that it would be ultra-precise. While the net movement would indeed be small and you could count on it to be accurate, the amount of play in the design would devour its precision. On average it would be amazing, but not usefully reliable at any specific point.
Torque: “Gear up for speed, gear down for torque”, so this must have astronomical torque, right? Well, in theory there is enough mechanical advantage for a single man to win a tug-of-war against all of Manhattan Island — when fabricated from imaginary materials. In reality, the plastic the gearbox is made from (or steel, or tungsten, or carbon nanotubes) will hit its limit many orders of magnitude before that mechanical advantage could ever be applied. Van Deventer does point out that the design actually handles torque better than most other gear systems, but nowhere near enough.
Vibration: Oskar shuts this one down himself. Grinder gears grind and sound like dogs on a bone. Even if the net wobble in the gearbox is eliminated, it still shakes and shudders.
Long-Term Measurements: Perhaps this could be used to measure or affect something that spins very fast, over a very long period of time? 24/7 spinning as fast as one can would result in not even one output rotation over the course of an entire month. Material strengths here again are in play; it seems far more likely that the gearbox would wear itself out (“grinder” is an apt description) long before a single rotation could ever be completed.
It still reduces speed, so, whatever purpose it may someday serve would probably revolve around an application where speed change alone is valued and not its typical tradeoffs of torque and precision.
Product Before Market
This gearbox is an interesting case study of Maker culture and the accessibility of technology. We live in a world where an idea that does something that has never been done before can be built at home and shared without cost (so that it can be reproduced by anyone else also at home), all without it having any use or any place in the market. Outside of art, that is something we did not have a few years ago.
Most inventions are driven by a need to solve a problem for a certain price. Burdening innovation with the chains of both usefulness and profitability has merits for efficiency in a factory, but the investment here is minimal.
Divorcing these three components and letting crowdsourcing handle the unsolved pieces means we will get to see a lot more unbridled innovation in the future. That is going to mean a lot of chaff (and perhaps in the end this gearbox is among it), but it also means we are going to achieve things we otherwise would not have.
If you can fill in a piece of the puzzle, Oskar would love for you to leave him a comment.