10 ms·

Stringbike: Chain-free bike

42 points by Maro 16y ago

JoeAltmaier 16y ago
Movie is confusing - do the wires change length? How is the leverage applied to the hub? Why not a movie of the bloody bike?
- nkassis 16y ago
  Yeah I'm confused too. Looking at it, it seems like the string is elastic and pedaling builds tension or some thing like that.
  - stcredzero 16y ago
    Watch the movie. It's a compound pulley. The string is actually a cable and it is not at all elastic.
    - JoeAltmaier 16y ago
      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!
      - smcl 16y ago
        I'm with you, I mean there's obviously an explanation but why not make it absolutely crystal clear in the video?
- rsbrown 16y ago
  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?
  - oconnore 16y ago
    The chain goes on one side of the bike.
    - rsbrown 16y ago
      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.
      - silentbicycle 16y ago
        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.
  - stavrianos 16y ago
    Having only one chain drastically simplifies the derailer problem, I should think. Also, you spend half as much on gears and chain.
- TGJ 16y ago
  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.
  - ianferrel 16y ago
    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.
- jcl 16y ago
  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.
- maggit 16y ago
  They have much more interesting videos on the homepage of stringbike itself: http://stringbike.com/ http://stringbike.com/ 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%20driving%20units http://www.stringbike.com/Internal%20symmetry%20of%20both%20...
nkassis 16y ago
Not sure I see the advantage of this design. I'd try a belt driven bike first: http://en.wikipedia.org/wiki/Belt-driven_bicycle http://en.wikipedia.org/wiki/Belt-driven_bicycle.
oconnore 16y ago
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.
- jacquesm 16y ago
  That's been done on regular gears, I'd imagine it would work much the same: http://en.wikipedia.org/wiki/Biopace http://en.wikipedia.org/wiki/Biopace
  - adamtj 16y ago
    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.
    - oconnore 16y ago
      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?
      - arethuza 16y ago
        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.
      - adamtj 16y ago
        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.
nuriaion 16y ago
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.
- rtyuioikujhy 16y ago
  It's zero maintenance. For 'serious' bike riders who care about efficiency and clean/oil chains it's useless. For riders who use the bike for one week/year, put it away when it rains and never touch it otherwise it's great
babo 16y ago
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.
silentbicycle 16y ago
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.
- stcredzero 16y ago
  A problem which will hardly exist with a readily available guard and an internal hub shifter.
  - silentbicycle 16y ago
    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.
    - Poiesis 16y ago
      No modding needed with the recently released, cheesily named Sturmey-Archer S3X. It's an internally-geared three speed fixed gear hub: http://www.sturmey-archer.com/products/hubs/cid/3/id/47 http://www.sturmey-archer.com/products/hubs/cid/3/id/47 .
      - silentbicycle 16y ago
        Nice! I didn't know they'd released it, thanks for the heads up. Time to build a new wheel. :)
babo 16y ago
Some more videos at http://www.youtube.com/user/stringbike http://www.youtube.com/user/stringbike
eli 16y ago
Couldn't you just put a second chain on the other side? Or am I missing something in this "symmetry" argument?
- Tichy 16y ago
  Perhaps it would be difficult to keep them in sync, and if they are not in sync, chaos ensues. No idea, though.
JoeAltmaier 16y ago
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.
eldenbishop 16y ago
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".
- utexaspunk 16y ago
  I don't see any reason why one couldn't put a ratcheting hub in the crankset, allowing backward pedaling...

42 points by Maro 16y ago

Movie is confusing - do the wires change length? How is the leverage applied to the hub? Why not a movie of the bloody bike?

nkassis 16y ago
Yeah I'm confused too. Looking at it, it seems like the string is elastic and pedaling builds tension or some thing like that.
- stcredzero 16y ago
  Watch the movie. It's a compound pulley. The string is actually a cable and it is not at all elastic.
  - JoeAltmaier 16y ago
    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!
    - smcl 16y ago
      I'm with you, I mean there's obviously an explanation but why not make it absolutely crystal clear in the video?
rsbrown 16y ago
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?
- oconnore 16y ago
  The chain goes on one side of the bike.
  - rsbrown 16y ago
    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.
    - silentbicycle 16y ago
      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.
- stavrianos 16y ago
  Having only one chain drastically simplifies the derailer problem, I should think. Also, you spend half as much on gears and chain.
TGJ 16y ago
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.
- ianferrel 16y ago
  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.
jcl 16y ago
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.
maggit 16y ago
They have much more interesting videos on the homepage of stringbike itself: http://stringbike.com/ http://stringbike.com/ 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%20driving%20units http://www.stringbike.com/Internal%20symmetry%20of%20both%20...

nkassis 16y ago

Not sure I see the advantage of this design. I'd try a belt driven bike first: http://en.wikipedia.org/wiki/Belt-driven_bicycle http://en.wikipedia.org/wiki/Belt-driven_bicycle.

oconnore 16y ago

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.

jacquesm 16y ago
That's been done on regular gears, I'd imagine it would work much the same: http://en.wikipedia.org/wiki/Biopace http://en.wikipedia.org/wiki/Biopace
- adamtj 16y ago
  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.
  - oconnore 16y ago
    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?
    - arethuza 16y ago
      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.
    - adamtj 16y ago
      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.

nuriaion 16y ago

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.

rtyuioikujhy 16y ago
It's zero maintenance. For 'serious' bike riders who care about efficiency and clean/oil chains it's useless. For riders who use the bike for one week/year, put it away when it rains and never touch it otherwise it's great

babo 16y ago

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.

silentbicycle 16y ago

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.

stcredzero 16y ago
A problem which will hardly exist with a readily available guard and an internal hub shifter.
- silentbicycle 16y ago
  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.
  - Poiesis 16y ago
    No modding needed with the recently released, cheesily named Sturmey-Archer S3X. It's an internally-geared three speed fixed gear hub: http://www.sturmey-archer.com/products/hubs/cid/3/id/47 http://www.sturmey-archer.com/products/hubs/cid/3/id/47 .
    - silentbicycle 16y ago
      Nice! I didn't know they'd released it, thanks for the heads up. Time to build a new wheel. :)

babo 16y ago

Some more videos at http://www.youtube.com/user/stringbike http://www.youtube.com/user/stringbike

eli 16y ago

Couldn't you just put a second chain on the other side? Or am I missing something in this "symmetry" argument?

Tichy 16y ago
Perhaps it would be difficult to keep them in sync, and if they are not in sync, chaos ensues. No idea, though.

JoeAltmaier 16y ago

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.

eldenbishop 16y ago

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".

utexaspunk 16y ago
I don't see any reason why one couldn't put a ratcheting hub in the crankset, allowing backward pedaling...