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Auto-Shift Bike

automatic bike transmission
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like cars, bikes now have many more gears than just one. So, design an automatic transmission that can work on a bike to optimize your efficiency for the few of us that have trouble shifting gears on our bicycles (guilty.) also like a car, this might have a low gear activated manually, for steep hills and things.
fischerman, Apr 16 2011

Shimano auto-shift system https://bike.shiman...eps/auto-shift.html
Not much drag on the driveline - but nothing beats a clean and tight fixie [a1, May 01 2023]

[link]






       ummmm... Google came up with over 1.8million results for "bicycle automatic transmission" including videos.
FlyingToaster, Apr 16 2011
  

       Welcome to the Halfbakery, [fischerman].
normzone, Apr 16 2011
  

       Don't feel bad, we've all done it.   

       Okay, well I have, anyway.
Alterother, Apr 17 2011
  

       Well, yes you definitely have.
FlyingToaster, Apr 17 2011
  

       [fischerman], check out the help file over there on the left, under meta. It's an entertaining read and will be a great help to you. We all had to read it as preparation for the quiz (you heard about the quiz, didn't you?)
normzone, Apr 18 2011
  

       If you're thinking of motorcycles, that's already done too. Most scooters have a belt type CVT. There have been a couple of bigger bikes built with more conventional automatic transmissions, but it's not good. When you have substantial power available, the prospect of an unexpected gearshift in mid corner is unappealing. The natural layout of motorcycle controls doesn't force the rider into a choice between shifting and other controls. Motorcyle gearchanges are very light and quick. There is not enough to be gained from auto transmission to justify the extra weight and power drain.
Twizz, Apr 18 2011
  

       [marked-for-deletion] Widely known to exist, I'm afraid.
jutta, Aug 05 2012
  

       BUT WAIT! While out on a ride today I thought of a brilliant and new way to do this.   

       Googled when I got home… dang … Shimano is offering exactly the thing I had in mind.
a1, Apr 29 2023
  

       Efficiency is the big problem with any modification to the way bicycles work. When the thing is being pedaled by a person, they tend to be extremely intolerant of inefficiency. As a baseline, bicycle chain/sprockets are >95% efficient, current gear change mechanisms change the ratios, but leave the chain/sprocket system intact.   

       Shaft drives have been tried, but even the relatively marginal power losses of ~5% or so means everyone hates them. The other problem is managing the relatively large torque generated by humans ~200 ft/lbs, in a package light enough not to hurt efficiency. Even something as thoroughly tested and famously reliable as a Sturmey-Archer 3 speed AW hub gear is on the edge of the possible, fit a bigger sprocket than the 16t default and there's a good chance you'll strip the gears.
bs0u0155, May 01 2023
  

       Shimano's system integrates technology they've honed separately - cadence and torque sensors in the crank, electric shifting at the derailleur. Regardless of weight and complexity, it doesn't impact the efficiency of the chain and gears.
a1, May 01 2023
  

       Had one of these, perhaps early 90s? Centrifugal weights on the freewheel assembly controlled up- and downshifts. It worked quite well until it didn't: the mechanism seized briefly and then quietly exploded. Never did find all the component pieces.
whatrock, May 04 2023
  

       You must have been going impressively fast. Though the modern Shimano design isn’t like that spinning weight thing of the 1990s.
a1, May 05 2023
  
      
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