Half a croissant, on a plate, with a sign in front of it saying '50c'
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speed multiplier

Planetary Gearbox changes bicycle gearing; commuting as we know it
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(1st post, plz be gentle) I think that the reason more people dont bicycle to work is because the distance to work and the fact that most people cant keep up a high enough cadence long enough to get anywhere worthwhile (7 to 10 miles) without getting up two to three hours earlier. I dont want to get up extra early, but id like to cover more ground once in a while. Enter the Planetary gearset. With cranks set up to support and power the planetary carrier we could easily multiply the operator output RPM by the number of teeth on the gears. It would be conceivable to overdrive output by a factor of five (this somehow feels attainable). Using the planetary gearset wed go from about a comfortable 55-60 rpm at the cranks to a respectable +-300 RPM at the output Sun Gear. Using about a 22 tooth front cog we would drive a regular 7 or 6 speed freewheel ( im afraid of breaking the chain with 8/9) with a really low first (34+) gear for the stop n go deal. The other gears would also increase in size due to the reduction in torque brought about by the gearbox, but the overall increase in output speed would be axceptable. Think of a human powered two stroke... We could use it in quadracycles and with a little electric assist be rid of our dependancy on foreign oil. The human powered vehicle that actually goes fast!
Alpharaul, Feb 01 2007


       The range of gear ratios on a normal bicycle are pretty well matched with typical human power output and cadence. These ratios, as they are, are optimised to give maximum attainable speed under a range of conditions.   

       Dramatically altering these ratios won't bring about any benefit to ground speed, as the existing limitations of human performance, gradient, and wind resistance will remain unchanged.
Texticle, Feb 01 2007

       FYI 55-60 is a very low cadence, although common among novice cyclists. Select gears with the view to maintain around 90-110 rpm and you'll see a big improvement in ground speed.   

       Welcome to the hb.
Texticle, Feb 01 2007

       //planetary gearset wed // so it's really an idea concerned with outfits that you wear at weddings in outer space, but it pretends to be about bicycles....obviously another fan of the great and wonderful: 'The Third Policeman' ? - say YES and retain your first ever croissant here ! (be prepared for close questioning first though)
xenzag, Feb 01 2007

       Alpharaul, if only this works...but it doesn't. What is reponsible for your speed is 'Power'. The speed of the crank, or gears, is not so important (except matching to the best ability of the human body).
The power output of someone won't change if you change the gearing.
By the way, 7-8 miles/2-3 hours? That's slower than walking speed. Most reasonably able people, after a few weeks, can get an average speed of around 15mph. Compare to a car on a B road in the UK - an overall journey might be at an average of around 30-35mph. A bicycle is surprisingly fast in that respect.
Ling, Feb 02 2007

       Bicycles have had epicyclic gearing and greater-than-unity ratios for ages. Is the idea simply to have the ratios even higher?
angel, Feb 02 2007

       Pedalling at anything less than 90 RPM is bad for your knees--I know from long experience.   

       A person develops more power at higher RPM--compare it to your two-stroke engine and its high revs.   

       And power is the limiting factor to speed, not gearing. This idea won't help you go faster.   

       I have a little rant about the unlikelihood of suggesting an improvement in any old technology, but won't paste it in here as you are new.   

       Welcome to the Halfbakery.
baconbrain, Feb 03 2007

       //A person develops more power at higher RPM--compare it to your two-stroke engine and its high revs.//   

       I'm not unfit! I 've just got a very narrow power band.
Ling, Feb 04 2007

       thanks yall, Im going back to that drawing board w more determiantion than ever. Ill get something to stick yet.
Alpharaul, Feb 15 2007

       the bicycle dérailleur is one of the most elegant of engineered devices that has ever been conceived. It is light, durable, repeartable, stable and does its job extraordinarily well. Many modern bicycles are equipped with more than 21 different gear ratios ranging from "Damn I can barely move this thing"(the Lance Armstrong hill climb gear) to "I could pedal at 1000 rpms for a week and lot make it to work"(the joe nobody halfway before we get tired hill climb gear) I do not see how your idea can possibly improve on this.   

       Welcome to the HB, your off to a positive start.
jhomrighaus, Feb 15 2007


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