Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Automatic gear changing bicycle

  1. Sep 30, 2009 #1
    hi..

    i want to make a automatic gear changing bicycle in which instead of manual changing of gears they change automatically with variation of speed....

    for this project i need help..if you know any thing about this then please reply...by posting
     
  2. jcsd
  3. Sep 30, 2009 #2

    berkeman

    User Avatar

    Staff: Mentor

    I actually saw an infomercial for this type of bike a few months ago. Have you tried googling for a match? I'll try if I have time...
     
  4. Sep 30, 2009 #3

    i m waiting for your reply....i tried googling but i don't find anything useful..
     
  5. Sep 30, 2009 #4

    Mech_Engineer

    User Avatar
    Science Advisor
    Gold Member

    You want to design and build an automatic shift bicycle, but you can't even figure out how to search on Google for what's out there? :cry:
     
  6. Oct 1, 2009 #5
    i get many things related to the topic but they are not easily understandable......some of them are patents and some are just description.....
     
  7. Oct 1, 2009 #6

    minger

    User Avatar
    Science Advisor

    Maybe you could also look at a continuously variable transmission (CVT). It might actually reduce the complexity of having switches and things to decide when to change gears, etc, etc.
     
  8. Oct 1, 2009 #7

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    There have been a few autochanging bikes - but it's generally much easier to make them that change up as you peddle faster. Making ones that can change down as you peddle slower or allow you to change down while not moving are a lot harder.
     
  9. Oct 1, 2009 #8

    minger

    User Avatar
    Science Advisor

    More on my point, a quick google shows that quite a few CVTs are available for motor scooters. They seem to run around $100. It seems to me to be very reasonable alternative if you're interested.

    I think it will be quite difficult, as mgb mentioned to get it back into a lower gear.
     
  10. Oct 1, 2009 #9

    Mech_Engineer

    User Avatar
    Science Advisor
    Gold Member

    Instead of using the pedals, just make the transmission use the speed of the back wheel as the shift reference. When you slow down, it automatically gets you into a lower gear, and as it speeds up it goes into a higher gear.
     
  11. Oct 1, 2009 #10

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    If you think of the rear dérailleur it's easy to make it go into a high gear - if you take the spring off a normal unit the weight of the hanging part will pull the chain into the smallest cog (highest gear) but to make it go down (lifting the hanger and moving to a higher gear) you need a very strong spring.
    In practice this puts so much friction on everything that you can't move it.

    There have been a few attempts at a hub gear with a clutch (really a preselect) to switch into bottom gear automaticaly once you have stopped. But none of them seem to have caught on.

    A sprung split plate+belt style CTV could work but they are heavy and inefficient compared to a bike chain.
     
  12. Oct 1, 2009 #11

    berkeman

    User Avatar

    Staff: Mentor

  13. Oct 1, 2009 #12
    I'd use something like a opposed con variable drive the used the tension pull on the chain to sense the load. it would gear down as the pull was harder, and ease up as the pull reduced

    dr
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Automatic gear changing bicycle
  1. Bicycle Gearing Question (Replies: 30)

Loading...