Herb wrote: These numbers went through my subconscious last night. How do you come up with these high speeds? My physics may be foggy but wouldn't an average speed of 125% that of the downward speed also mean that the recovery crank would travel 25% further? This is obviously not the case.

I don't know if the numbers are exactly correct, but the recovery crank wouldn't have to travel further, just as the power crank isn't traveling a shorter distance. The eccentric cam does the "trick", doesn't it? Your power crank is traveling a little slower while your recovery crank travels a little faster than the average speed of the two. Isn't that right? It's not a distance thing, but a speed thing.

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

Herb wrote: "These numbers went through my subconscious last night. How do you come up with these high speeds? My physics may be foggy but wouldn't an average speed of 125% that of the downward speed also mean that the recovery crank would travel 25% further? This is obviously not the case. "

I guess it is how you define recovery. If it is the part of the stroke that is above the average speed, then it would appear that the "recovery" distance is about 125% of the "power" distance. If it is between BDC and TDC then it is not. I was using recovery in the Rotors physiolgic sense.

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Frank,
An original Ironman and the Inventor of PowerCranks

OH, I see now what you mean by "distance". You mean the distance along the arc traced by the pedal spindle during each part of the stroke. Certainly, your use of the term "distance" is now clear regarding RCs.

I've a mental picture of a different device (that doesn't even exist that I know of!) that was contaminating my understanding. The idea that messed with my mental picture of "distance" is a sliding crank-arm lever that extends some on the downstroke and retracts some on the upstroke. Like I said, it's only a mental picture, not a real device. But, with my imaginary crank-arm, the pedal spindle would, indeed, be traveling a further distance on the power stroke and shorter on the recovery stroke. This would maximize power available from the extensors while minimizing the distance the flexors would be asked to move the pedal. I don't even know if such a device is buildable...it's fun to think about, though! What a radical change of pedalling technique if it were to be built, though! I should get it patented in case it is possible to make work!

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

I realize this is only an academic exercise, not real-life, but I'm talking about actually decreasing the total distance of the recovery pedal spindle and actually increasing the total distance traveled by the power spindle, i.e., if you have a 175 mm crank arm, an arc of 175mm is constant throughout the revolution. The thing I'm imagining would vary the crankarm length so that you would have a longer than 175mm crankarm on the power side and shorter than 175 on the recovery side. Like I said, it's only an idea in my mind, not an actual device, at least, not that i know of!

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

Interestingly (and happily), Rotor Cranks designer/developer Pablo Carrasco has himself just weighed in from Madrid on the other thread...

[reply]I realize this is only an academic exercise, not real-life, but I'm talking about actually decreasing the total distance of the recovery pedal spindle and actually increasing the total distance traveled by the power spindle, i.e., if you have a 175 mm crank arm, an arc of 175mm is constant throughout the revolution. The thing I'm imagining would vary the crankarm length so that you would have a longer than 175mm crankarm on the power side and shorter than 175 on the recovery side. Like I said, it's only an idea in my mind, not an actual device, at least, not that i know of![/reply]

Actually, Paula Newby-Fraser used a device similar to what you describe for a time during the 90s. I don't know if the prototype ever came to market or not. There's a photo in the latest Triathlete Magazine of her old bike on page 92. You can see the crankset, but it's hard to really see what it does. The hanging section extended the cranks on the downstroke, and released to shorten them on the upstroke. I recall them being featured and demonstrated during the TV coverage of a race during the time she used them, and I believe that she used them for around 5 years or so.

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"that which does not destroy me will only make me stronger" Frederick Nietzsche
andrew peabody
http://BREAKAWAYMULTISPORT.COM

Cool! Didn't know that!

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

  Gary please explain,
Rotor cranks are guaranteed for 2 YEARS but if
you use them in competition the warranty is void.
If you cannot use them in competition, why
would the manufacturers expect you to buy them?

Herb, I didn't realize the cranks rotated around different centers...that's exactly what I was trying to imagine a sliding mechanism would be able to do. I was simply showing my ignorance about the device! Thanks for pointing it out...it certainly makes sense to do SOMETHING along these lines, at least to my small brain.

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)