Right, watching the movie, the cable gets longer and shorter but nothing on the rear hub moving/winding that would explain that. In fact the hub seems to be moving in the opposite direction!
Also, there's no explanation of the symmetrical aspect of the design. I'm intrigued by it, but other than vague allusions to its superiority over asymmetrical designs no analysis is given.
So, I ask HN: why aren't chain/belt bike designs symmetrical?
Sorry, my question was unclear. Why do traditional chain designs only have the chain on one side? If symmetrical designs are more efficient (as the article claims) why couldn't the same thing be accomplished with a chain/belt design?
EDIT: as to the article -- more analysis of why symmetrical designs are superior would have been nice.
The added weight from a second complete drivetrains (chains, gears, derailleur) and/or extra mechanical complexity would probably negate the efficiency gained by better transmission of force.
Think of the system on the back wheel like a tape measure. The string is inside wound around the axle. As the pedal moves the string is pulled out winding the axle and turning the wheel.
I think the advantages are because of the location of the torque. When the left pedal exerts force, it torques the left side of the bike which coincides with the the natural movement of the bike. Imagine when a cyclist pedals very hard and the bike sways from side to side from the force exerted on the pedals. Now I'm not sure if they are trying to reduce the movement of the bike, or make it feel more natural.
The thing I cannot make out is the switch from gears to a single system. Is the output of work the same as the force going in, which would mean that you have to pedal the same amount going up a hill as going down, or is there a variability of work like a rowing machine? The rowing machine system would seem to apply here but they do not address that so I'm not 100% on that.
It wasn't clear, but I believe that shifting gears would be accomplished by moving the pulley that's attached to the triangular frame on the pedals along the axis of pedal rotation. Move it closer to the pedals, and you downshift.
This could be done continuously, rather than having discrete gears.
I think what happens is that the wires are fixed length, but wrapped around a ring on the back axle. As the pedal is pushed down, it moves the pulley, unwrapping the wire from the ring, which rotates the rear wheel through a ratcheting mechanism.
I'm not sure what causes the wire to rewrap itself around the ring on the upstroke... probably some sort of embedded spring.
Neat. I wonder if creating a vertical elliptical pedal path, or even a linear path would be an improvement. That way the cyclist would have more leverage on the down stroke, since at the bottom of a circular stroke you are forcing the pedal mostly rearwards, not downwards.
Also, to me it looks like the two rotating cylinders next to the rear wheel are ratchets, like a socket wrench.
It's my understanding that the pros don't use this. If you don't have enough torque, you're probably doing it wrong, and would soon be out of gas even with more mechanical advantage. Shift down, pedal faster.
This makes no sense. If you can generate the same power with less physical exertion, and no significant reduction in reliability or weight, why not take it?
I've seen comments about gear changing being slightly worse (which doesn't surprise me) and being overshadowed by things like moving from clips to SPD pedals.
Physical exertion equals power. You can't have the same power with less physical exertion. It's a trade-off between aerobic capacity and anaerobic capacity. You can pedal in a high gear, using more strength, or you can pedal faster in a lower gear, maintaining the same speed, but using more cardiovascular capacity. In both situations, if you are going the same speed, you are putting out the same amount of power.
Non-circular gears change the gear ratio as you pedal. It effectively shifts down in that part of the pedal stroke where you have the least strength. Since the bike doesn't slow down, your feet must speed up. Then, when your feet swing around to where you have more strength, it effectively shifts up.
My argument is, if you are pedaling at the limit of your strength, you are in too high a gear. Shift down and spin your feet faster. You'll use less strength, and more aerobic capacity, enabling you to maintain an equivalently high power output, but for longer. It's easier to run a marathon at a constant speed than to sprint 100 m at a time, taking walking breaks to maintain the same average speed.
Isn't your analogy in the last paragraph a good argument in favour of non-circular gears? Gears that allow you to output the same amount of power all the time.
Oval chainrings (like Biopace, Rotor Q-Rings, etc.) are used by some pro cyclists. The oft-touted advantage for the system is the elimination of the "dead spot" at the top of the pedal stroke, but it still seems to very much be a case of personal preference. Just like there are some pros that prefer to spin an easier gear up a climb, while some would rather mash it out in the big ring.
It all comes down to how good the motor (legs+lungs) is.
It's funny how people are so resistant to innovation.
"Biopace chainrings are often cited as the epitome of a solution looking for a problem among the biking press."
While typing on a computer that likely contains a mechanical hard drive spinning at close to 10krpm, the author complains of a slight increase in mechanical complexity that will allow him/her to generate more power. The real question is whether or not the complexity is manageable, will it break down frequently? etc.
"People are so resistant to innovation" is one way to look at it. Another way to look at it is that sometimes innovation gets far enough ahead of expectations that it can't overcome challenges with user education and linkages to present technology.
I remember using Biopace and the part I remember the most was going up a steep hill and losing traction because of the change in torque. I was riding a bike the way I was accustomed to pedaling but the power output would surge because of the change in mechanical advantage. Maybe I could relearn how to pedal so I could take advantage of Biopace but I really just wanted to ride, not maximize every degree of the pedal arc.
I've usually found pedalling mostly downwards inefficient, because it pushes me off the seat. If I want to get power out of pedalling, I put particular care into pedalling back and forth - the top foot forwards, the bottom foot backwards. For this to work well, though, you need pedal straps or very toothy pedals.
I don't see where this design has a big advantage above a traditional chain. Maybe their is less oil/grease so your trousers will be happy.
But the efficiency of a chain is something around 97% (IMHO). I think with so much moving parts etc. the efficiency will be lower. And i think that the forces will be problematic to handle.
The inventors talks about similarity with current hard drives where he got the original idea. While this design sounds complicated, it replaces the whole drive chain, including gear shift.
Chain-free bike designs (and other major hardware changes) come up periodically. Typically, they're belt-driven. While chains and cables for brakes seem inferior to cables and hydraulic brakes, they degrade for more gracefully. It's not a perfect solution, but it's a reasonable local maxima for most people. Professional racers can get away with equipment that's wildly impractical for commuters, mountain bikers, etc., though.
"Although, that would presumably be the least of your worries if a fast-moving, taught, metal wire lashed off its piston next to your leg. Ouch." I've had a couple chains break or skip off (especially on fixed-gear bikes, which don't have a derailleur or chain tensioner to regulate chain slack), and having a taut wire whip at my ankle sounds like a terrible idea. Getting a bit of grease on my ankle or pant leg is rare, and at most a minor annoyance.
Or you can just roll up your pant leg, wear shorts, or use a velcro strap (depending on the season). It's really not a serious problem, either way.
I usually ride singlespeed or fixed (much better on snow!). I've read about modding 3-speed internal hubs into 2-speed fixed internal hubs, but haven't tried.
Of the current non-chain solutions, the Gates belt system actually seems like a good idea for a commuter bike. Zero maintenance, long life, no grease, and quiet.
The design in the wired article, while interesting, seems like an overly complicated solution to the chain "problem".
> "[The] asymmetry [of traditional designs] has been the source of lots of problems"
I'd like to hear more about that. Sure, the rear wheel is balanced a little differently to account for this, and I imagine the feel is a little different if the both pedals are directly attached to the "cranks" (or their equivalent pulleys here), but I don't see a lot of problems caused by the asymmetry of a traditional design. Am I just blind to it? What are these problems?
For people going for the lightest bike possible, the spokes in the driving direction of the wheel are a smaller gauge (heavier)-- not one side or the other, as the hub is a single piece. The frame is reinforced slightly on the chain-side of the bicycle. But these modifications are for racing bikes, normal bikes have no special reinforcement because the weight difference is a couple ounces.
The current system has no problems and most parts are interchangeable.
Much of the complexity seems to be directed at keeping the pedals going around in a circle. Why not levers or some other reciprocating motion? ANything would work with cables.
The only drawback I can see to this system is that you can't spin the pedals backwards while coasting. I do this a lot to stretch my legs and just to pass the time on hills when I don't feel like speeding up. Peddling backwards will engage the forward motion "but along a miserable curve".
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[ 0.17 ms ] story [ 114 ms ] threadSo, I ask HN: why aren't chain/belt bike designs symmetrical?
EDIT: as to the article -- more analysis of why symmetrical designs are superior would have been nice.
I think the advantages are because of the location of the torque. When the left pedal exerts force, it torques the left side of the bike which coincides with the the natural movement of the bike. Imagine when a cyclist pedals very hard and the bike sways from side to side from the force exerted on the pedals. Now I'm not sure if they are trying to reduce the movement of the bike, or make it feel more natural.
The thing I cannot make out is the switch from gears to a single system. Is the output of work the same as the force going in, which would mean that you have to pedal the same amount going up a hill as going down, or is there a variability of work like a rowing machine? The rowing machine system would seem to apply here but they do not address that so I'm not 100% on that.
This could be done continuously, rather than having discrete gears.
I'm not sure what causes the wire to rewrap itself around the ring on the upstroke... probably some sort of embedded spring.
The lowermost video on this page shows the real bike from an angle where you can see what happens to the wires:
http://www.stringbike.com/Internal%20symmetry%20of%20both%20...
Also, to me it looks like the two rotating cylinders next to the rear wheel are ratchets, like a socket wrench.
http://en.wikipedia.org/wiki/Biopace
Non-circular gears change the gear ratio as you pedal. It effectively shifts down in that part of the pedal stroke where you have the least strength. Since the bike doesn't slow down, your feet must speed up. Then, when your feet swing around to where you have more strength, it effectively shifts up.
My argument is, if you are pedaling at the limit of your strength, you are in too high a gear. Shift down and spin your feet faster. You'll use less strength, and more aerobic capacity, enabling you to maintain an equivalently high power output, but for longer. It's easier to run a marathon at a constant speed than to sprint 100 m at a time, taking walking breaks to maintain the same average speed.
It all comes down to how good the motor (legs+lungs) is.
It's funny how people are so resistant to innovation. "Biopace chainrings are often cited as the epitome of a solution looking for a problem among the biking press." While typing on a computer that likely contains a mechanical hard drive spinning at close to 10krpm, the author complains of a slight increase in mechanical complexity that will allow him/her to generate more power. The real question is whether or not the complexity is manageable, will it break down frequently? etc.
I remember using Biopace and the part I remember the most was going up a steep hill and losing traction because of the change in torque. I was riding a bike the way I was accustomed to pedaling but the power output would surge because of the change in mechanical advantage. Maybe I could relearn how to pedal so I could take advantage of Biopace but I really just wanted to ride, not maximize every degree of the pedal arc.
For riders who use the bike for one week/year, put it away when it rains and never touch it otherwise it's great
"Although, that would presumably be the least of your worries if a fast-moving, taught, metal wire lashed off its piston next to your leg. Ouch." I've had a couple chains break or skip off (especially on fixed-gear bikes, which don't have a derailleur or chain tensioner to regulate chain slack), and having a taut wire whip at my ankle sounds like a terrible idea. Getting a bit of grease on my ankle or pant leg is rare, and at most a minor annoyance.
I usually ride singlespeed or fixed (much better on snow!). I've read about modding 3-speed internal hubs into 2-speed fixed internal hubs, but haven't tried.
The design in the wired article, while interesting, seems like an overly complicated solution to the chain "problem".
> "[The] asymmetry [of traditional designs] has been the source of lots of problems"
I'd like to hear more about that. Sure, the rear wheel is balanced a little differently to account for this, and I imagine the feel is a little different if the both pedals are directly attached to the "cranks" (or their equivalent pulleys here), but I don't see a lot of problems caused by the asymmetry of a traditional design. Am I just blind to it? What are these problems?
The current system has no problems and most parts are interchangeable.