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i want to know about the complete design and dimensions of the shaft and suggest me to give more efficiency to the bicycle

Móż
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ytfhgv ikj
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  • I think we need a few more details, i.e. are you intending to do a hardtail or soft tail. Is it for an MTB or a road bike. – Henry Jan 22 '16 at 19:27
  • Efficiency to the transmission system specifically, or efficiency to the bike overall? Chain drive is considered to be the highest efficiency available. Total weight comes into it too - a shaft will have to be hollow. Where does the freewheel/coasting happen, or will it be a fixed gear? Could add brakes on the driveshaft. For added complexity, consider a 2 wheel drive. – Criggie Jan 22 '16 at 19:57
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    As an me student you should be able to design the shaft. Your biggest problem is a gearbox to spin the shaft at the crank. And then alignment at the wheel as you have the chainstay to deal with. If you run a chain to a gearbox it kind of defeats the whole idea. I suggest you start bamboo shaft mock up. Do you have a plan B project? – paparazzo Jan 22 '16 at 19:58
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    So you want to do the design, starting with us giving you the design? How is this not "please do my homework for me?" – Móż Jan 22 '16 at 21:51
  • There have been shaft-driven designs in the past -- probably some creative Googling will dig up some info on them. – Daniel R Hicks Jan 22 '16 at 23:45
  • You need to decide right off whether there is suspension or not between the driving (rear) wheel and the rest of the bike. Suspension makes it MUCH more complicated since you need to allow for motion somewhere along the shaft. – Daniel R Hicks Jan 22 '16 at 23:46
  • Without suspension the main decision is with regard to the right-angle shaft connections at crank and rear hub. These need to be non-bulky (not adding too much to the width of the crank shaft and rear axle), they need to provide the right gear ratio, and they need to be able to withstand considerable torque. – Daniel R Hicks Jan 22 '16 at 23:50
  • https://en.wikipedia.org/wiki/Shaft-driven_bicycle – Daniel R Hicks Jan 22 '16 at 23:51
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    http://bicycles.stackexchange.com/questions/20591/any-experience-with-shaft-driven-bikes – Daniel R Hicks Jan 22 '16 at 23:53
  • Bottom brackets with integrated gear-boxes exist. Geared hubs exist. A shaft-drive would have to connect these in the most elegant (i.e. weight saving) way. – Carel Jan 23 '16 at 08:57

2 Answers2

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Always remember, cycling technology is driven by reducing the weight of the bicycle. Having a shaft that weighs half the weight of your bicycle is something you should avoid.

These are consideration when building a shaft:

  • Weight: 500gram to 1kg heavier than normal chain drive is ok, 1-2kg kg is not bad, but over 2kg+ is terrible.
  • Strength: must be able to withstand torque of at least 200 N.m, in practice it could be 3-4 times the minimum. Apart from the torque, you need to analyse the hoop strength. For example, the shaft should not break under normal drop/horizontal impact. I cannot tell you how thick and how big the shaft should be, because different materials will result in different design.
  • Compatibility: how you integrate the shaft driven into a normal frame. Bevel gear is a good start. Design a bevel gear appropriate for cycling is the next. Don't integrate a heavy bevel gear, which was designed for car/industrial machine, into your shaft. Design it yourself, shave as much weight as possible, but keep it as strong as possible.
  • Gearing: Start with single gear, or integrated gear hub. It is the easiest way. If you are using single gear, having a bicycle that is more than 11 kg is undesirable. Also check gearing ratio. Design a pinion (part of bevel gear) that could be threaded into the single gear wheel. (Last time I remember it is some imperial 1.375x24 tpi or something close to that)
  • Torque: for the same weight, shaft-drive is at great disadvantage comparing to chain-drive regarding maximum deliverable torque. So, again consider gearing appropriately so that the torque is as small as possible.

Aiming to build a shaft driven bicycle for efficiency is the wrong direction. Efficiency improvements of shaft over chain driven in bicycle is negligible. Not to mention, shaft driven is overshadowed by an (un)established market regarding gearing on bicycle.

Advantages of shaft driven:

  • Low maintenance
  • Better durability
  • Slightly better efficiency over time, since it requires less maintenance
  • Can be driven with high-torque, very good for some of the electric mid-drive motor

Disadvantages of shaft driven

  • Heavy. However, with the cost of carbon fiber being driven down, a carbon shaft designed for bicycle might just be light and economical just as a chain driven.
  • Expensive when repair/replace, again, market is the keyword
Nhân Lê
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  • Specifically, you have an allowable loss in the drivetrain of 2% under optimum conditions. More than that and your design is less efficient than a chain drive bike. So start by coming up with a pinion drive that loses less than 1% (you have two, one each end of the shaft). – Móż Jan 22 '16 at 21:54
  • Great answer. You can add shaft 'wind up' as another disadvantage. Whenever you ride hard you can really notice the shaft twisting under each pedal stroke due to the fact out output is not constant. I remember reading somewhere that our peak torque is higher than a small internal combustion engine. This makes designing a shaft drive difficult due to the need to also keep it light. – Rider_X Jan 23 '16 at 05:40
  • @Rider_X "small IC engine" as in 4 cylinder turbo, not small as i 900c Japanese eco. 100kg rider on 170mm crank = 170Nm – Móż Jan 23 '16 at 05:45
  • @Mσᶎ - I believe a bit smaller like a motor scooter or small motorcycle. It will take some work to track down the source. I remember being excited that we at least beat a lawn mower. – Rider_X Jan 23 '16 at 05:59
  • @Rider_X Now I have no idea what you mean. 170Nm is ~125foot-pounds and Car Torque List says that fts in with a Lotus Elise, Toyota Yaris or Toyota MR2. Likewise this list of "high torque motorcycles" has them around 90-110 foot-pounds and calls the one with 150 foot-pounds "obscene" – Móż Jan 23 '16 at 06:26
  • @Dont forget that those engine can run at a much higher RPM, that is why they can output a lot of power. A bicycle RPM on crank is around 50-130 RPM, which is about 20-30 time less than an automative – Nhân Lê Jan 23 '16 at 10:31
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    @NhânLê - yes agreed, but torque is what causes shaft wind up and on a shaft driven bike the shaft will experience two wind up and release cycles per pedal revolution which is pretty harsh relative to a drive shaft in an engine, which will experience a wind up at the start of power delivered but will remain wound up due to the more constant power delivery of an IC engine. – Rider_X Jan 23 '16 at 18:58
  • @Mσᶎ - I didn't realize that so many car engines had so little torque. I am not much of a car person. – Rider_X Jan 23 '16 at 19:07
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Here's some prior art for you to search out...

Reader "Unclemiltie" reminded me that America's first billionaire, John D. Rockefeller, loved to ride his bike, and was still riding in his 80s. It's a little bit ironic that he made his fortune at the helm of what was then the world's biggest oil company, which greatly enabled America's love affair with the automobile. This Library of Congress photo shows him posing with his shaft-drive Columbia bicycle.

From http://bikeretrogrouch.blogspot.co.nz/2016/01/the-non-politics-of-riding-bike.html

Rockefeller with his bike

Unfortunately he's standing in front of the interesting bits. However we can see that there is no chainring. There are also no brakes, so his bike was likely a fixed single-speed. To me this implies a toothed ring gear at the front and at the back, with a fixed drive shaft between them. As a plus it would pedal backwards as well as forwards, but no gearing. Lubrication of the gears is likely an oil bath, like a car's differential.

Criggie
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