ok guys, here is chance to hit on a tech issue with these interesting devices.
i reckon i note that they work by speeding a guy’s leg thru the recovery phase and getting it up there to the 1:00 position so it can hammer while the other leg is still inside the 6:00 position hammering. one might say it is similar to 'front qudrant swimming", perhaps - only in this case it is “front half pedalling”, as it were. got that.
so, for a given distance at a given cadence a rider spends more time in the "power’ phase of the pedal stroke, correct?
the qustion that occurs to me is this: why then - in addition to going a tad bit faster - would the rider not ALSO become a tad bit more tired? he is jamming more work into the same time and distance, so why is the net effect somehow mysteriously better, or more efficient? why isn’t it just a matter of more effort equals more speed . . . . . . and . . . . . more fatigue?
so, for a given distance at a given cadence a rider spends more time in the "power’ phase of the pedal stroke, correct?
First rule in dynamics – there is no free lunch. Second rule – it’s always possible to convince somebody there is.
The rotorcranks allow the downward foot to push the upward foot around the last bit of the circle a little faster than it otherwise would go. So, the downward foot is doing more work than on regular cranks: it’s pushing the bike forward and also pushing the other foot more quickly through part of the circle. So, while you might “feel” like you’re spending more time in the “power phase”, it comes at a cost – higher torque at part of the circle. There is also the possibility for higher cost due to the acceleration of the upward-moving crank as it pushes up against the recovering foot.
So, if we were to model this mechanism attached to, say, a motor, we would find no benefit, by simple extension of first principles. Actually, a slight loss due to the additional friction of the mechanism.
But, the human body is not a motor, and some people would argue that there is a net benefit to moving part of the workload around the circle and concentrating it more in the “power phase”. I dunno. I’ve traded emails with some pretty smart folks who are studying these things closely, and the jury is still out. So far, nobody I know (or trust) with access to a lab-quality ergometer and a set of Rotorcranks says they provide a benefit.
yes julian. i was intentionally leaving the bit about the energy to accelerate the recovering foot out of it. perhaps our rotorcranker is yaquicarbo, and he is able to utilize his powercrank trained legs to keep them out of the way!
and, the bit about the added friction lets just call a wash, for now.
but, the " no free lunch" thing is exactly what i am driving at. if i ride 100 meters at a cadence of 100 in a 100 inch gear on a rotor bike and a regular bike i will spend more time with my legs in the driving downward position on the rotors. presumably i will go a little faster. also, i will get a little more tired. it just doesn’t seem like all that great a bargain, to me, from this perspective.
oops. well if i am at the same rpm in the same gear i guess i will not go faster, eh?
but you get my meaning. and i yours, i think. the same work is getting done, just rearranged a little. add in the parts about the energy to accelarate that other leg, friction losses, etc, and i am left wondering what the poop is.
ok ok. so, for a given gear and given cadence we see the recovery leg moving faster thru means of the linkage, as compared to a regular crank. hence, the driving leg must be moving slower than a regular crank in this gear at this cadence.
is this where rotor proponents perhaps see their benefit? that for a given gear and cadence your driving leg is maybe feeling smoother and …i dunno . …more powerful?
It is not hard for me to believe that rotors provide benefit. But of course it would come at a cost. It seems to me (in a very simplified explaination) that rotor cranks try to make the most use of what tends to be the strongest/most fit muscle groups in a cyclists legs. (Quads and glutes??) This requires an increased load on those groups. No free lunch, work is just shifted to what are typically more fit muscles. The question is how much additional load can these muscles take on?
“why then - in addition to going a tad bit faster - would the rider not ALSO become a tad bit more tired? he is jamming more work into the same time and distance, so why is the net effect somehow mysteriously better, or more efficient? why isn’t it just a matter of more effort equals more speed . . . . . . and . . . . . more fatigue?”
you nailed it, and as I say on the web site, they are not magical “perpetual motion machines” giving you something for nothing
yes, Rotor cranks do require more effort on the downstroke but at the same time increase the rider’s speed, while not raising the HR or lactate levels
so that said, you will ride with more power, but “empty your gas tank” faster
something that you cannot do with traditional cranks WITHOUT raising your heart rate and lactate levels
What you may be missing in the equation, is that muscles and bones are MORE efficient at certain angles. If the most efficient angle of a person’s foot/knee/hip coincides with the area on the curve that is the slowest (or hardest) in the pedal stroke, I can see where it would indeed result in a greater power output.
The conservation of energy stuff is good when looking at a machine…humans aren’t machines.
Assuming they do work (the amount has yet to be laboratory quantified to my knowledge) the only possible mechanism that I can figure is that they slow down the powerstroke such that the muscle is contracting more efficiently than it does when having to shorten faster.
What you may be missing in the equation, is that muscles and bones are MORE efficient at certain angles. If the most efficient angle of a person’s foot/knee/hip coincides with the area on the curve that is the slowest (or hardest) in the pedal stroke, I can see where it would indeed result in a greater power output
A good idea that hasn’t borne careful scrutiny in athletes given time to adapt to changes in position and joint angles. Not surprisingly, runners have a “most efficient” angle that is more upright than cyclists. Take any given cyclist – whether they always sit straight up or always ride in the hooks – and change how they sit. Their efficiency goes down. Give them six weeks to adapt, and it goes back up.
The human body is remarkably adaptable. There is no single “best” set of angles.
There is yet another scientific test underway from a well respected “major sports (testing) facility in the U.S.” as we speak - results available Spring 2005
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Julian wrote: The human body is remarkably adaptable. There is no single “best” set of angles.
I agree…I’m referring to the tendency of a movement system to be most powerful at a certain angle of the joint. For example, the quads may be most powerful at 142 degrees…knee still flexed, but not quite straight. While the hips may be more powerful at a more acute angle…maybe because the lower back muscles come into play more at a more acute hip angle…anyway, IF, when all the factors effecting efficiency are factored together and there exists a “more efficient” angle of attack that coincides with the hardest part of rotation of the rotorcrank during a pedal stroke, THEN the rotorcrank benefits would be easy to explain.
First rule in dynamics – there is no free lunch. Second rule – it’s always possible to convince somebody there is.
Actually there is free lunch sometimes at least when it comes to the amount of effort that is needed by you to perform a task. If the rotorcranks some how allow you to apply more force or at least the same amount of force with less energy expended over normal cranks then I would say that was free lunch.
Best example of free lunch is when your trying to move something heavy like a large rock and you use a long stick and a fulcrum, or a point of leverage to help with the movement. The amount of energy required by you would be much less than if trying to move it without the long stick and fulcrum. Of course you could have someone else do it and eat their lunch.
RVW wrote: The fact that muscles may work better when you turn them on and leave them on, instead of turning them on and off all the time.
This phrase: “turn them on and leave them on” may be describing one of the benefits of a slightly more acidic environment in the muscle-energy availability system…
Best example of free lunch is when your trying to move something heavy like a large rock and you use a long stick and a fulcrum, or a point of leverage to help with the movement. The amount of energy required by you would be much less than if trying to move it without the long stick and fulcrum.
Sorry to be nitpicker, but in your example, each alternative takes the exact same amount of energy to move the rock! If you move the rock the same distance in the same amount of time, then each alternative also takes the exact same amount of power to move the rock. You merely trade force for velocity over two different distances of application. Newton, et. al., wrote out all the equations for this stuff three centuries ago.
There is no free lunch. The only possible positive effect to Rotorcranks (or Powercranks or anything else mechanical on a bike) is *IF *they allow the body to operate its muscles more optimally, as yaquicarbo has posited and as Gary Tingley and Frank Day have argued. I don’t know the answer to that – I just want to make clear the distinctions.
And, BTW, “efficiency” (the conversion of the energy stored in glucose/fat into power instead of into heat or more storage) is only part of the equation of “optimal.” We can be very efficient on a bike and still hit the fatigue wall more rapidly than a less efficient cyclist that is doing something different.
Studies of cadence show that lower (70-75) is usually better if we simply focus on efficiency. If we instead focus on time to complete a sufficiently long course (a combination of efficiency and fatigue-resistance), we find that higher cadences are optimal (75-90).
Julian concisely wrote: The only possible positive effect to Rotorcranks (or Powercranks or anything else mechanical on a bike) is *IF *they allow the body to operate its muscles more optimally.
dang, I wish I would condense this idea so well. Thanks. Again.
got that.