What keeps a bike upright?

[slto...@gmail.com]

https://www.nature.com/news/the-bicycle-problem-that-nearly-broke-mathematics-1.20281

Of course this isn't for John or Frank who could fall down if they were sitting on the ground.

[Frank Krygowski]

On 1/4/2019 11:37 AM, slto...@gmail.com wrote:
> https://www.nature.com/news/the-bicycle-problem-that-nearly-broke-mathematics-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

[Sir Ridesalot]

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 gyroscoptic 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

[John B. Slocomb]

Well, Tom is a little slow on the uptake.

cheers,

John B.

[John B. Slocomb]

On Fri, 4 Jan 2019 10:43:12 -0800 (PST), Sir Ridesalot
<i_am_cyc...@yahoo.ca> wrote:

>On Friday, January 4, 2019 at 12:28:54 PM UTC-5, Frank Krygowski wrote:
>> On 1/4/2019 11:37 AM, slto...@gmail.com wrote:

>> > https://www.nature.com/news/the-bicycle-problem-that-nearly-broker-mathematics-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.

[slto...@gmail.com]

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.

[Frank Krygowski]

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

[John B. Slocomb]

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.

cheers,

John B.

[Ralph Barone]

Hard braking, coasting down steep hills and mounting/dismounting
disregarded, of course :-)

[John B. Slocomb]

Correction. should have read "riding high wheelers".

cheers,

John B.

[Jeff Liebermann]

On Fri, 4 Jan 2019 08:37:24 -0800 (PST), slto...@gmail.com wrote:

>https://www.nature.com/news/the-bicycle-problem-that-nearly-broke-mathematics-1.20281
>Of course this isn't for John or Frank who could fall down if they were sitting on the ground.

It's the optional kickstand that keeps the bicycle upright.

Bicycle Dynamics
<http://bicycle.tudelft.nl/schwab/Bicycle/>

The Stability of the Bicycle by David L. Jones:
<http://www.phys.lsu.edu/faculty/gonzalez/Teaching/Phys7221/vol59no9p51_56.pdf>

How Do Bikes Stay Up?
<https://www.youtube.com/watch?v=oZAc5t2lkvo> (3:56)

Why bicycles do not fall: Arend Schwab at TEDxDelft
<https://www.youtube.com/watch?v=2Y4mbT3ozcA> (17:55)

--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[John B. Slocomb]

If I member the discussion was confined to balance but from what
little I've read about them mounting wasn't a major problem, and just
from looking at them I doubt that hard breaking was either, from the
simple friction brake pressing on the tire that appear to be used.
Some trishaw's here use this system and "hard braking" is not an
applicable term for them either. A more descriptive term is something
like "slow and decorous" :-)

cheers,

John B.

[slto...@gmail.com]

I would be willing to bet that if you reversed the steering so that you mentally do so that it would have been a great deal more ridable.

[John B. Slocomb]

I suspect that a rear steering bike might be similar to a rear
steering fork lift in that it turns around the front wheels as apposed
to a more conventional vehicle that turns around the rear wheels.

If you have ever tried to back a car a long way backward at any speed
over a slow walk you will notice a similar problem.

Given that turning a bicycle also involves balance I can see how a
rear steering bicycle might be rather difficult to ride :-)

cheers,

John B.

[Frank Krygowski]

I've ridden two or three of them, just short test rides probably no more
than a mile. Yes, they are very easy to balance. The analogy I use is,
it's like the difference between balancing a yardstick vs. a one-foot
ruler. The yardstick's higher polar moment of inertia gives a lot more
time for corrections. Except balancing a high wheeler is more like
balancing a broom with the brush end up. You have forever to catch any tilt.

(For the same reason, balancing a recumbent is more tricky until you get
used to it.)

Mounting turned out to be no trouble at all. You put your left foot on
the little step attached to the bike's backbone, give one scoot with
your right foot, and gracefully ascend to the seat. Dismounting was no
harder, just find that foot rest and reverse the procedure, although
experts can dismount in flashier ways.

The riding experience is sort of majestic. The view is wonderful. The
pace is slow (or at least, was for me) and the machine is very stable.
Going uphill is not easy, though. Of course there's no downshifting, but
ISTR that the riding position wasn't as suited for putting out lots of
pedal force. I never tried to stand up to pedal, and wonder if it's even
possible.

Downhill would, I think, be frightening. You're almost directly over the
contact patch of the big wheel. Braking at even 1/10 gee would send you
over the bars, and hitting a rock might do the same thing. Normal
pedaling postion, with your legs under the handlebars, would guarantee a
Superman imitation, but with less success. That's why the really gutsy
ones would hook their legs over the bars while coasting fast downhill.

One friend who owned one has since passed away. Another friend has two
of them, and has done a century on one - a feat I find amazing. Aside
from the leg strength required for climbing hills, the aero resistance
is immense. One does not ride very fast, so 100 miles must require
considerable time in the saddle.

--
- Frank Krygowski

[Sir Ridesalot]

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

[Andre Jute]

The one I've always liked best
http://www.phys.lsu.edu/faculty/gonzalez/Teaching/Phys7221/vol59no9p51_56.pdf
just upped and did the experiments on the bike he rode to work. Today's "scientists" would probably start the same test by demanding a budget of at least $5.6m...

Andre Jute
Saddened, and not much wiser either...

[slto...@gmail.com]

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.

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.

[slto...@gmail.com]

So if you purposely take someone that has ridden a normal bike and make the steering non-instinctive it requires a time to re-learn? Whoever would have thought?

[Frank Krygowski]

On 1/6/2019 9:40 AM, slto...@gmail.com 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

[Sir Ridesalot]

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

[AMuzi]

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

[AMuzi]

Well, except that the rider will accelerate into the
pavement face first with a hard application of the brake. I
have not done this myself but rider reports from the early
1880s are graphic enough.

Advantages and shortfalls, features and foibles:
http://3.bp.blogspot.com/_6hUBbm9EVm8/SlQx5f_rdLI/AAAAAAAAASA/Wg_UCVe4_tY/s400/high+wheelerfendingdog.jpg

[Ralph Barone]

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.

[news18]

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.

[slto...@gmail.com]

Front wheel drive is easily possible now. I have no idea why they don't use it but it requires nothing more than a single universal joint at the steering head.

[slto...@gmail.com]

The difficulty is the time required for the rear wheel steering to effect a turn vs the immediate action of a front wheel steering. There's nothing different in the actual operation of the bike.

[Mark J.]

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.