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Elliptical pedal stroke

Cycle up steep hills
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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.

The_Saint, Mar 07 2011

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]

[link]






       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.
hippo, Mar 07 2011
  

       //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.
pocmloc, Mar 07 2011
  

       What's needed is a CVT coupled to a flywheel to even out the energy pulses from the rider.
8th of 7, Mar 07 2011
  

       //why it was that it was easier to get off my bike and push it up the hill than actually pedal up the hill//   

       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.   

       This means instead of putting out that effort over 15 minutes, you're putting it out over 5 minutes, a much harder proposition.   

       * 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.
MechE, Mar 07 2011
  

       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.
MechE, Mar 07 2011
  

       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.
The_Saint, Mar 07 2011
  

       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.   

       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.
MechE, Mar 07 2011
  

       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.
MechE, Mar 07 2011
  

       //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.
FlyingToaster, Mar 07 2011
  

       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" )
Dub, Mar 07 2011
  

       How about a cammed CVT whereby different cams can be selected to stress or relieve specific joint/muscle groups.
FlyingToaster, Mar 07 2011
  

       //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!   

       (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.)
mouseposture, Mar 08 2011
  

       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.   

       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   

       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.
metarinka, Mar 08 2011
  

       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.   

       [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.
The_Saint, Mar 08 2011
  

       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.   

       //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.
pocmloc, Mar 08 2011
  

       // cammed CVT //   

       <points reproachfully at earlier anno>   

       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.
8th of 7, Mar 08 2011
  

       // cammed CVT //   

       <points reproachfully at earlier anno>   

       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.   

       And they exist - they're called "stepper bicycles".
8th of 7, Mar 08 2011
  

       // And they exist - they're called "stepper bicycles". //   

       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.
The_Saint, Mar 08 2011
  
      
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