h a l f b a k e r yClearly this is a metaphor for something.
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A little while ago, while trying unsuccessfully to pedal up
a
very steep hill, I wondered why it was that it was easier
to
get off my bike and push it up the hill than actually pedal
up the hill. Besides my complete lack of skill and fitness,
it
occurred to me that the pedal stroke is very
different to
the walking stroke which is elliptical rather than circular.
In fact, standing there and walking in small circular steps
proved every bit as inefficient as trying to pedal up the
hill.
The normal walking pattern gives leverage that would be
very useful when cycling and so I tried to dream up an
elliptical cycling mechanism. My first thought was for a
double shaft system whereby a second shaft attached to
the pedal shaft would effectively double my leverage on
the down stroke and then become redundant during the
backwards up and over stroke. Disappointingly I found
this
had already been done (see link) although it was only
recommended for recumbent bikes since the pedal
becomes 'floppy' and could hit the ground.
So my thought then is for a crank arm that extends to
double length for the down stroke and shortens for the
backwards up and over stroke. This could be done with a
hydraulic crank arm that follows an elliptical guide.
There
will be a small amount of efficiency loss in the hydraulics
having to 'push and pull' the pedal however the leverage
gain should be significantly greater. I do realise that
'real'
cyclists weld their feet to the pedals and apply pressure
through the whole cycle however this is a solution for us
casual cyclists.
Second crank shaft
http://www.hostelsh...ccessory=1026425305
[The_Saint, Mar 07 2011]
Biopace Chainwheels
http://en.wikipedia.org/wiki/Biopace
Vaguely related. Changes the torque with an oval chainwheel. [AntiQuark, Mar 08 2011]
rotor crank
http://autobus.cycl...eviews/rotor_cranks
Varies timing of pedals away from static 180 deg [metarinka, Mar 08 2011]
Stepper bicycle
http://www.youtube....watch?v=yc1UkCcKXz8
Somebody pleading for money to get their stepper bike funded [The_Saint, Mar 08 2011]
Walking uphill with bicycle
http://www.thirdwav...ke/bike-o-shoes.jpg
[ldischler, Mar 09 2011]
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Annotation:
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Much easier to do this by fitting elliptical chainrings on your bicycle. These have been around for ages - opinion is divided as to whether they're really helpful. |
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//why it was that it was easier to get off my bike and push it up the hill than actually pedal up the hill// Your bike is over-geared. Most are; if you have 2 bikes in a shop, one normally geared and one over-geared, people prefer to buy the over-geared one because it looks sportier and faster. So the shops save money by not offering the sensibly geared option. |
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What's needed is a CVT coupled to a flywheel to even out the energy pulses from the rider. |
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//why it was that it was easier to get off my bike and push it up the hill than actually pedal up the hill// |
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Simple answer, it isn't. As [poc] says, your bike doesn't have a low enough gear. It takes less total effort to ride up the hill (barring wind resistance, which isn't a problem for a begining rider on an uphill) than to walk it. You were, however, trying to ride up at least 3* times as fast as you would walk it. |
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This means instead of putting out that effort over 15 minutes, you're putting it out over 5 minutes, a much harder proposition. |
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* If you're a beginning rider you're not going to be stable much below 6mph, a person walking up hill pushing a bike is lucky if they make 2 mph. |
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Oh, and I know a cyclist who has recently started doing triathalons (shudder) and he states that running up hill is easier than running on level ground because the uphill running stride more closely resembles a cyclists pedal stroke. |
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A number of your comments miss the point a bit.
IF I train and exercise the appropriate muscles and
perfect the art of spinning rather than mashing
then the bicycle can be efficient but what if I
don't? Should we then accept that the bicycle can
only be efficient under those circumstances or
should we attempt to change the technology to
adapt more to the way humans work? I don't
accept either that I don't have a low enough gear -
I have 18 possible permutations and adding a 19th
isn't going to change much. The eliptical chainring
doesn't solve the problem either since it doesn't
change how much force I can exert, it changes
what happens to the force once I have exerted it.
Envisage the pedal at 2 o'clock. With a standard
length crank arm there is only so much force that I
can exert but if I were to double the length of the
crank arm then I can double the amount of torque
that force produces. |
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In order to get that extra force, you are going to have to extend move your leg twice as far. Given that a properly setup bicycle is already using the total length of available leg extension, you are either going to hyper extend and contract the knees, or you are going to get exactly the same amount of power out of a much more complex system. |
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What you really want, I think, is a pedal that is in a cam-slot such that during the initial downstroke it slides in along the crank arm, and then back out once you pass the midpoint. This produces the truly elliptical motion that you seem to be looking for, but using this sort of stroke is going to destroy your knees, as there is a sudden transition from a strong down force to a backward motion. This is the same reason why eliptical chain rings have never caught on. |
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As a note, the linked pedal pendulum is intended for riders who have restricted mobility in one leg, and thus are willing to accept greatly decreased power in exchange for being able to use the leg at all. It is intended to allow the rider to gradually adjust as they regain use of the leg. |
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//why it was that it was easier to get off my bike and push it up the hill than actually pedal up the hill// That might have had something to do with the effort and concentration it takes to keep from falling over sideways at a low speed. |
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I think eliptical grears are very-much baked - A bike I had more than 10 years ago had an elliptical chainring (Search "Shimano elliptical chainring" ) |
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How about a cammed CVT whereby different cams can be selected to stress or relieve specific joint/muscle groups. |
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//The Wankel Cross-trainer// Friends, Romans, and
countrymen! Don't look a fool, in your last hours, huffing
and puffing on the way to Golgotha. Order a Wankel Cross-
trainer today! |
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(Sorry, [The_Saint], couldn't resist. Seems like a good idea,
to me, according to this reasoning: Gearing only optimizes
the muscles' velocity-tension relation, while your idea
should, in principle allow optimization over the whole
length-velocity-tension surface. Theoretically.) |
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a similar Idea was the rotor crank. It varied the
timing of your pedals so that the legs weren't at
top dead center and bottom dead center
concurrently I.E the pedals weren't 180 degrees
apart. Also like ignition advance for your feet. At
TBD and BDC you generate no power so there's a
logical thought for why you would want to
moderate that. |
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The idea worked well but to my knowledge didn't
catch on, due to price for the amateur and
unwillingness to change/ rules for pros |
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After all recumbant bicycles are far more efficient
but banned from competitive bicycling, the
standard fair bicycle design is far from optimal in
terms of man/machine interface. Rowing is the
most efficient means of human to machine power,
but probably not practical for a bike. walking and
running are very efficient, however you can't
extract energy because when you run or walk
basically you're shifting your center of gravity in
front of your body and making your legs constantly
catch up. |
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Many thanks for the inputs. I believe I now have
the recipe for the most efficient bike possible. It
should have training wheels for low speed
stability, 19 gears and a rider facing strobe light. I'll
give it a try and let you know how I get on. |
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[Dub] - I noted earlier that the elliptical chainring
is not the same solution as it doesn't vary how
much torque I can apply through the pedals but
how much of that the torque that is applied is
converted to forward momentum. |
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O Holy one, it is nothing to do with spinning, or training, or having all of 18 gears. It is to do with the rage of those gears. Is the lowest of your 18 so low that you can turn the pedals with no effort on a 1 in 5 hill? Does the bike fall over even when you pedal like a demon? If not, then the gear is too high still. Otherwise, you just need to pedal like a demon and concentrate on your balancing. Or switch to a tricycle. |
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//change the technology to adapt more to the way humans work// This line of thinking leads inexorably to a self-propelled armchair i.e. a motor-car. |
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<points reproachfully at earlier anno> |
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Since the legs only transfer power on the front part of every downstroke, what's needed is a "push - push" system where the pedals oscillate up and down alternately, and drive the conventional sprocket through a linkage. |
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<points reproachfully at earlier anno> |
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Since the legs only transfer power on the front part of every downstroke, what's needed is a "push - push" system where the pedals oscillate up and down alternately, and drive the conventional sprocket through a linkage. |
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And they exist - they're called "stepper bicycles". |
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// And they exist - they're called "stepper
bicycles". // |
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Thanks for that, I must admit I was starting to
think that a step mechanism of some sort would
be more productive since the crank arm could be
much longer and you could limit the stroke to just
that part of the stroke that is effective. I hadn't
heard of stepper bicycles but a quick Google
shows
that they are growing in popularity. The Youtube
link I have posted seems to explain the principles
quite well. |
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