Wednesday, September 22, 2010

15 String Transmission

It looks like one of those linear drive systems have shown their face again. It was in 1897 that a patent, granted to a teen Swedish inventor Birgin Ljungström, showed the world a linear drive bicycle where the pedals moves in linear, reciprocating fashion. The project was sponsored by dynamite inventor Alfred Nobel. Ofcourse, numerous other linear drive systems for bicycles have been invented since then.

Recently shown on the Internet by a Hungarian bicycle design team was a linear drive bicycle. The system we're looking does involve circular pedal motion but the symmetric cam mechanism ensures that a string or rope constantly winds and unwinds on both sides of the bike, transmitting torque through the freewheel of the rear hub. Some videos are attached below to show the design and operation of the drive.

Discuss the possibilities and negative aspects offered by a symmetric drive system such as number of extra moving parts, ease or difficulty of adjustment, gear ratio variability, safety etc.


  1. My major concerns are-
    The friction/load at the wheel on the pedal arm is probably pretty high.

    At speed, will the hub be able to wind up fast enough or are you going to get string slack?

    The motion looks anything but smooth, esp when trying to spin at 80+rpm

  2. Knees will take a severe beating from the whiplash action at the bottom of the pedal stroke.

    Not sure I see any advantages to this design.

  3. Too much moving parts = complicate and constant mantainance;

    That movement on the rear hub - forward / backward, plus the thin laether-like wire, pulleis, etc tends to accumulate a lot of dirt. Think that all drivetrain should be enclosed to assure parts stay clean.

  4. Too complicated. Pointless and doesn't offer any significant advantage over a chain system to convince me to change. Next....

  5. What is the claimed advantage?

  6. Useful post. You keep churning out some good info!

  7. Anonymous6:22 PM

    Hm, where does my rear disc brake go?

  8. Anonymous6:25 AM

    At a high cadence the return of the oscillating frame at the top of the pedal stroke will be too fast causing vibration, excessive wear and will likely begin to flick aggressively back in to place for the next stroke, possibly way too fast for the controlled placement of the drive wire/string. I doubt the knees will have an easy time of the motion either.

    The big plus is to see new ideas, and I welcome that, but as has been found many times in the past, the diamond frame and chain drive are very, very hard to beat.

  9. Anonymous4:52 AM

    This must be the worst day in the history of the cozy beehive. Contador busted while Armstrong is still a free and innocent (until proven guilty) man :)

  10. Anonymous8:05 AM
    Read and weep, Ron. And we thought Landis was lame!

  11. Mechanically the concept is groovy and remarkable, but I don't see the point or advantage since it overly complicates a very simple drive train mechanism that bicycles currently employ.

  12. Anonymous5:57 AM

    Well, the original design from 1897 has a big advantage to the current crank mechanism:

    If you look at the position of a pedal of a normal crank drive, the lever arm of force starts at 0 Newton (0 degree), goes to it's maximum (90 degree) and back to 0 Newton (180 degree). The torque curve shows a sinus wave therefore. The old design from 1897 doesn't have this disadvantage, as no crank drive was used.

    The ungarian design unfortunately combines the disadvantages of both, the crank drive (sinus torque curve) and the linear drive (complex mechanical design)...

  13. Anonymous9:56 PM

    I just came across this -- looks mighty similar, from 30 years ago (if the link doesn't work, Google for "biocam bicycle of the future")

  14. At first I was wondering what the point of all that complexity is... it seems like lot of elaboration for no perceptible benefit.

    But then I noticed this system allows for ratios to be spread optimally, rather than the deal you get with derailleur gears where the higher the ratios, the bigger the gaps the between them, which is opposite to optimal.

    If this system actually works well in practice (contrary to the impression it's given via these vids), it could represent a worthwhile development... and if it doesn't, maybe it could inspire something that does.

    I don't think this was a waste of time.

  15. Anonymous4:22 PM

    Already noted above, the BioCam system from Facet in the early '80s is essentially the same and better.

    Here's further info.

    Very, very few things in the cycling world, indeed in life, are actually new.


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