Cadence drive transmission
In addition to my RBS, I’m also working on a transmission that would have a constant cadence. The pedaling effort would wind a constant force spring and the spring force would drive the bike. It would be continuously variable and automatic shifting. The weight should be similar to a derailer system.
The ratio would only be 2:1 so it is not intended to compete with a 21 speed derailer setup. But it would be a nice step up over a fixed gear, or it could replace the crank gears and be used in conjunction with shifting hub gears. This would smooth out the cadence and require fewer gear shifts.
I would like to hear your thoughts as to whether I should pursue this?
Last edited by Paulc; 09-30-13 at 09:49 PM.
OK. I'm trying to picture this.
Pedals wind up a spring, say like a spiral clock/watch spring. Pedaling effort would be somewhat easier if the spring is close to unwound and higher when the spring is close to completely wound. Seems like you could pedal at any cadence you want, no?
Spring powers the rear wheel. A transmission would need to go between the spring output and rear wheel to match the spring force to the required driving force depending on speed, incline, etc.., right? How would you "throttle" the power? Perhaps you could shift to high gear to reduce driving force or to a low gear to increase it, so the transmission would serve as a kind of throttle.
Sounds like an interesting novelty, but not sure of the real benefit or commercial potential.
What happens if you need a burst of extra power, like climbing a hill?
In my proposed scheme, you'd downshift as I described. Once the spring power was exhausted, you'd be essentially pedaling directly.
Originally Posted by Retro Grouch
There were centrifugal shifters. With just 2 gears it hardly seems worth while to auto shift, something that could handle a full cassette would be more useful.
I'm sure a system could be built that would work fairly well. There would need to be logic to accommodate accelerating from a stop and sudden application of power. In both those cases it would be beneficial to allow cadences about 10-15 RPM faster than a cruising cadence. This would probably be easy to add to Shimano's electronic shifting, but its something their target market probably wouldn't want.
One situation where I frequently mess up shifting is coming out of a corner. I'll slow down and stop pedaling or soft pedal while down shifting, then start pedaling again at the apex. If I down shifted too many gears when I start pedaling again my feet spin uselessly. Might also be good for riding while eating / drinking.
Isn't your idea like an Autobike? That uses a NuVinci hub with an automated shifter (not sure how the shifter works).
A prior bike by the same name used a rear derailleur with spring-mounted weights that slid on the spokes to actuate a normal rear derailleur.
Try coasting down a hill on a tandem and making a decision on when to start peddling again. Shimano's Flight Deck computer's "virtual cadence" was good for that. It tells you what your cadence would be if you were peddling. It was fun to see if Mrs. Grouch and I could catch it right in the sweet spot.
Originally Posted by gecho