PDA

View Full Version : NuVinci CV hub



andy_b
08-18-2010, 11:08 PM
In one of Evan's motorized bicycle threads there was mention of a NuVinci hub:

http://www.fallbrooktech.com/nuvinci.asp

Have any of you ever messed around with one? They are the craziest-looking thing inside with all the balls and rollers. I just wonder how they hold up under human or low-HP applications.

andy b.

beanbag
08-19-2010, 01:17 AM
In one of Evan's motorized bicycle threads there was mention of a NuVinci hub:

http://www.fallbrooktech.com/nuvinci.asp

Have any of you ever messed around with one? They are the craziest-looking thing inside with all the balls and rollers. I just wonder how they hold up under human or low-HP applications.

andy b.

I demo'd one on a bicycle at the Sea Otter bike festival. It's pretty neat how you can continuously shift gears while under power. It's pretty much strong enough for a bicycle, and the rep claimed that people have used them on (what was it, scooters?) although that voids the warranty. Only three main problems with it. One is that it's expensive - approx $400 or so. Second is that it's heavy - approx 5 lbs or so. Third, the gear range is somewhat limited. I think the one they had was 360% range, whereas a mountain bike has a range of something like 500%.

djc
08-19-2010, 07:01 AM
...NuVinci hub:

http://www.fallbrooktech.com/nuvinci.asp

Have any of you ever messed around with one?

Don't know how they patented that; it looks identical to a Kopp variator.

If you are interested in the concept, this is another productive avenue for a search, including patents.

strokersix
08-19-2010, 07:35 AM
I've looked at one of these in person. One concern I have in a limited power application such as a bicycle is mechanical efficiency. I don't know the number for nuvinci but it's tough to beat a roller chain.

EVguru
08-19-2010, 08:15 AM
I've looked at one of these in person. One concern I have in a limited power application such as a bicycle is mechanical efficiency. I don't know the number for nuvinci but it's tough to beat a roller chain.

NuVinci compare the average efficiency of their drive as similar to a hub gear. That's lower than a derailer, but you've got to look at system efficiency, not one item in isolation. By always having the 'perfect' ratio available, you may improve the efficiency of the power source, i.e. human (or electric in the case of Greenpower racers) and achieve a higher overall efficiency.

The hub uses a special fluid to transmit the torque without metal to metal contact. The fluid turns to a near solid under pressure to transmit the force. It's nothing new, but there have been considerable improvements in reducting the hysteresis loss in the fluid over the years.

GadgetBuilder
08-19-2010, 10:38 AM
Stating mechanical efficiency is the thing that NuVinci studiously avoids, even when asked directly. They admit it is poorer than a derailer and say it is similar to a geared hub - so clearly they have made the efficiency measurements and just as clearly they refuse to share the results.

If the efficiency were good it would be touted in their specifications.

John

andy_b
08-19-2010, 11:37 PM
These efficiency numbers (which seem to be hard to find) would explain why some of the motorized bike guys have said the NuVinci gets pretty hot in use. I'll have to keep my eyes open for a chance to test one on a bike someplace local.

andy b.