More about the NuVinci CVPT hub

My last post about the NuVinci was skeptical. The label of "planetary transmission" can be misleading because traditional planetary systems are not continuous. With a little more research, I have discovered that the NuVinci is indeed continuously variable, and it is also pretty clever in design.

It it still difficult to see how the NuVinci works, even after watching the tech demo video on the Fallbrook Technologies website. I'd really like to get a model of it, one of those models with the cutaway to the inside, so you can see the parts moving and how it works. Sort of like those cut-in-half engines at an auto museam. Or maybe a working Lego model, or something. You can see the videos here.

I also found a whitepaper on the NuVinci with a good picture that might help you understand what is going on inside the hub.

This diagram shows the "idler" or the central channel that moves the ring of balls left and right, varying the contact point with the output disc. Through a special oil, the balls apply friction on the output ring, transferring torque from the rotation of the planets to the output disc, which gives motion to your wheel. This is an overly simplistic view on the technology, but it gives you the general idea of what is going on.

1. You twist your grip shift
2. The shaft of the hub moves the idler
3. The idler changes the contact point on the output disc
4. And you upshift or downshift, depending on how that contact point changes

Rather than touting the fun and simplicity of the NuVinci, I would like to point at how incredibly efficient the CVPT is. Not only can you shift under load and without pedaling, but there is infinity gear choices, withabsolutely no redundancy in gear ratios. Fallbrook claims that this system has a 360% gear range. I don't really know exactly what that means (except that it refers to the percentage of range from the lowest to highest gears, as measured in gear-inches), but I'll provide their very handy infographic for comparison.

To call the NuVinci a "planetary transmission" is a stretch of the term because it is barely recognizable as such. But it is still a planetary system because it has all the right components, from planets to the sun and a shaft that moves back and forth changing the gear ratios from input to output. There are plenty of testimonials online about the simple joy of using the NuVinci (which I sometimes mistakenly refer to as the NuvaRing, a very, very different product). I like the concept, it appeals to almost every single aspect of my tech-headedness, and I can't wait to combine the NuVinci with a belt drive on my mountain bike (for more belt drive NuvaRing insanity, please see the options for the Ellsworth Enlightenment).