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#22
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What keeps a bike upright?
On 1/5/2019 5:05 PM, John B. Slocomb wrote:
On Sat, 5 Jan 2019 10:29:06 -0800 (PST), wrote: On Friday, January 4, 2019 at 3:41:22 PM UTC-8, John B. Slocomb wrote: On Fri, 4 Jan 2019 10:43:12 -0800 (PST), Sir Ridesalot wrote: On Friday, January 4, 2019 at 12:28:54 PM UTC-5, Frank Krygowski wrote: On 1/4/2019 11:37 AM, wrote: https://www.nature.com/news/the-bicy...matics-1.20281 Of course this isn't for John or Frank who could fall down if they were sitting on the ground. You're just reading that now?? -- - Frank Krygowski Seems to me that the guy has made a few basic false assumptions. Any bicycle I've ever seen with the front fork in it's proper position soon falls over after being pushed without a rider on it. I also think that the gyroscopic force of rotating bicycle wheels keeping the bicycle upright is miniscule unless the wheels are turning at very high revolutions. I once saw a video on You Tube of a normal bike with the front fork reversed, and without a rider, that went quite a distance when pushed before toppling over. I think too that making a bicycle stable enough to be riderless might end up being extremely difficult to ride. Look at how even small changes in frame/trail geometry on a road bike creates quite different handling characteristics. Cheers There has been a lot of research into what makes a bike stable. One paper I read described a bike that was built with a front fork that allowed the trail to be adjusted from a negative number to a rather large positive number and yes "trail" has a great effect on the (would one say) the longitudinal stability of a bike - how easily the fork turns, and during the same experiment it was "discovered" that BB height, vertical location of center of gravity, also effected this same stability. Bikes have also been built with counter rotating wheels which counter act the gyroscopic effect of the spinning wheels. My own guess is that bicycles require stability in at least two planes and so far no one seems to have built a bicycle that is completely stable. cheers, John B. All you have to do is look at a Penny Farthing which had totally different geometry but not only was ridable but they raced them. That gives you some idea of just how odd a bicycle really is. Ridable? A bloke rode one across the U.S. in 1884.... and today people brag when they ride down a gravel road. There was a discussion here about riding wheelers some time ago and Frank, I believe, described riding one and apparently they are easier to balance then the more modern bicycles. They are indeed. The taller the wheel the easier to control. But as has been noted the geometry is unlike modern chain driven safety bicycles. -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
#23
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What keeps a bike upright?
Sir Ridesalot wrote:
On Sunday, January 6, 2019 at 11:01:48 AM UTC-5, Frank Krygowski wrote: On 1/6/2019 9:40 AM, wrote: I cannot see how you couldn't ride a rear steering bike as easily as a front steering bike remembering that you do not turn the wheel much and that would be a handicap since you couldn't determine how much you were turning the rear wheel by sight. If you did some reading on the "rear wheel steering" attempts people have made for decades, and the very limited success they've had, you might change your mind. If rear wheel steering were easy, almost every recumbent would use it because of the simpler and more compact drive train. -- - Frank Krygowski Just wondering if rear wheel steering would be easier if it was the FIRST method of riding a bicycle a person learned? That is like the almost unsteerable bike I linked to above, is it the learned behaviour of riding a normal steering bicycle that makes it so hard to ride a rear steering bicycle? Would a person who has never ridden a bicycle find a rear steering one so difficult? Cheers I believe that there's a positive feedback mechanism to rear wheel steering that makes it more "twitchy". When cars were playing around with four wheel steering in the 80s/90s, I seem to recall they were using in phase rear wheel steering at low speeds for tighter turning circles, but anti-phase rear wheel steering at high speeds for stability. |
#24
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What keeps a bike upright?
On Sun, 06 Jan 2019 06:40:57 -0800, sltom992 wrote:
As part of the driving test you are required to be able to back a vehicle up. Particularly as part of a Class B license exam. And it is quite easy to do since you look into mirrors and hence everything is shown in reverse. It is a skill that a lot of people forget very quickly. Try looking after the loading/unloading bay of a live steamers meet where it is vey common to carry their loco in a trailer. Trailer aside, It is the same with any "facility' that requires people to reverse in. I cannot see how you couldn't ride a rear steering bike as easily as a front steering bike remembering that you do not turn the wheel much and that would be a handicap since you couldn't determine how much you were turning the rear wheel by sight. Re-reasd the article you posted where he talks about how to front steer and then think how many people can safely adapt their skills to rear steer. |
#25
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What keeps a bike upright?
On 1/5/2019 7:26 PM, Sir Ridesalot wrote:
On Saturday, January 5, 2019 at 4:49:17 PM UTC-5, Frank Krygowski wrote: On 1/5/2019 1:29 PM, wrote: On Friday, January 4, 2019 at 3:41:22 PM UTC-8, John B. Slocomb wrote: On Fri, 4 Jan 2019 10:43:12 -0800 (PST), Sir Ridesalot wrote: On Friday, January 4, 2019 at 12:28:54 PM UTC-5, Frank Krygowski wrote: On 1/4/2019 11:37 AM, wrote: https://www.nature.com/news/the-bicy...matics-1.20281 Of course this isn't for John or Frank who could fall down if they were sitting on the ground. You're just reading that now?? -- - Frank Krygowski Seems to me that the guy has made a few basic false assumptions. Any bicycle I've ever seen with the front fork in it's proper position soon falls over after being pushed without a rider on it. I also think that the gyroscopic force of rotating bicycle wheels keeping the bicycle upright is miniscule unless the wheels are turning at very high revolutions. I once saw a video on You Tube of a normal bike with the front fork reversed, and without a rider, that went quite a distance when pushed before toppling over. I think too that making a bicycle stable enough to be riderless might end up being extremely difficult to ride. Look at how even small changes in frame/trail geometry on a road bike creates quite different handling characteristics. Cheers There has been a lot of research into what makes a bike stable. One paper I read described a bike that was built with a front fork that allowed the trail to be adjusted from a negative number to a rather large positive number and yes "trail" has a great effect on the (would one say) the longitudinal stability of a bike - how easily the fork turns, and during the same experiment it was "discovered" that BB height, vertical location of center of gravity, also effected this same stability. Bikes have also been built with counter rotating wheels which counter act the gyroscopic effect of the spinning wheels. My own guess is that bicycles require stability in at least two planes and so far no one seems to have built a bicycle that is completely stable. cheers, John B. All you have to do is look at a Penny Farthing which had totally different geometry but not only was ridable but they raced them. That gives you some idea of just how odd a bicycle really is. It's actually hard to build a bicycle that is not rideable. There's a somewhat well-known but quirky physics paper out there documenting a physicists quest to build an unrideable bike. As I recall, he tried several weird front end geometries, including doing away with trail entirely. He mounted a second front wheel next to the original and just above contact with the ground, which he rotated in the opposite direction to cancel any gyroscopic effects. As I recall, he could ride anything he built. But back in the early and most experimental days of modern recumbents (probably the 1970s) I read about a guy who tried to build a rear-steering recumbent, based on the idea that it would simplify a front wheel drive train. IIRC, that was almost impossible to ride. The variety of current bikes is pretty amazing - long and short wheelbase recumbents, small wheel folding bikes, kids bikes with questionable geometries, tandems, box bikes, tall bikes, long-tail cargo bikes. People ride them all. Handling on some can be a bit quirky, especially at first, but people adapt. And that's one of the main things about human beings: We're very adaptable. -- - Frank Krygowski Even this bicycle became ridable after months of practice by the adult. The child learned much quicker. I found it quite interesting. https://www.youtube.com/watch?v=MFzDaBzBlL0 Cheers Wow. Just wow. Video definitely worth watching, especially for those of us in (or formerly in) the teaching biz. I have never seen this video before, and yet feel like I've witnessed this transition in hundreds of students. Topics of cognition, meta-cognition, and "neuroplasticity." Mark J. |
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