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"The Stability of the Bicycle"



 
 
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  #61  
Old October 8th 03, 07:59 PM
Benjamin Lewis
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Default "The Stability of the Bicycle"

Simon Brooke wrote:

writes:

In spite of the garbled text, I don't see in what way this contradicts
steering a bicycle using these forces, if I deciphered it correctly.
By the way, have you performed this experiment or did you only read
about it? If you have done this, you'll note that the axle of the
wheel remains in a horizontal plane down rotation speed of the wheel
below one revolution per second.


OK, I've just done the experiment. 700c front wheel with tyre,
supported at one end of the axle (actually by the quick release lever
on the skewer). My observations are as follows:

* at 1Hz it just flops, falling to the axle vertical position in less
than one revolution.

* at 2Hz it loses about 20 degrees from the horixontal at each
revolution, falling to the axle vertical position in less than five
revolutions.

* at about 5Hz it loses about 10 degrees from the horizontal at each
revolution, but it's less easy to observe when the axle vertical
position is reached because of precessive effects.

Above 5Hz I wasn't able to time the speed of the wheel adequately, but
by observation it was about four or five times this speed before the
wheel would spin with the axle horizontal for any significant period
of time.

As Jobst says, this experiment is easily repeatable, but if anyone
argues with my results I'm quite happy to repeat the experiment on
film and post a quicktime movie.

1 Hz = .7*3.14 = 2.2 metres/sec = 8 km/h, approximately. So 5 Hz =
40 km/h, well above the speed at which no-hands riding becomes easy,
and at that speed a wheel cannot even keep it's own weight upright for
2 seconds.

I have to say I started this discussion unpersuaded either way, but on
the basis of this I'm now convinced that on normal bicycles operating
at normal speeds the gyroscopic effects are negligable.


You have shown they are negligible for holding the bike upright,
substantiating Jobst's claim that a bicycle is *not* held upright by
gyroscopic forces. It's the "precessive effects" that are relevant for
steering.

--
Benjamin Lewis

Never underestimate the bandwidth of a station wagon full of tapes.
-- Dr. Warren Jackson, Director, UTCS
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  #62  
Old October 8th 03, 09:05 PM
Simon Brooke
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Default "The Stability of the Bicycle"

writes:

Simon Brooke writes:

Actually, this report
URL:
http://www.geocities.com/CollegePark...32/pyfair.html
contradicts Jobst. It says that


'He reversed the front fork to nullify the caster action, and he
fitted a counter-rotating wheel on the front fork to effectively
nullify or cancel out the gyroscopic effects. When he was
finished, he still found that the bicycle could still be balanced
and steered quite easily... These experiments effectively
disproved the hypothesis that gyroscopic motion was the primary
force responsible for balance in a bicycle...'


There is one of the glaring failures of this report. There is mention
of riding no-hands mixed in with being able to control the bicycle.
In the above paragraph, one might assume he meant riding no-hands, but
in fact that is impossible and was not the case. Therefore, it does
not conflict with what I have said.


On the contrary he is quoted as explicitly saying he rode no hands.
See for example URL: http://www.dclxvi.org/chunk/tech/trail/

'...he found it difficult (although not impossible) to ride with his
hands off of the handlebars ...'

Dr Jones article is cited as
Jones, David E.H., "The Stability of the Bicycle", Physics Today
(April 1970): 34-40

I have not read it myself.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

;; in faecibus sapiens rheum propagabit
  #63  
Old October 8th 03, 09:13 PM
Carl Fogel
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Default "The Stability of the Bicycle"

wrote in message ...
Ian L? writes:

There are no "maths", math is an aggregate concept and has no
plural... except in GB maybe.


I guess you don't have a bicycle with a QR front wheel so you can't
perform the simple experiment of turning the wheel at "walking
speed" to fell the strong gyroscopic effect caused by tilting the
wheel manually to the left and right.


Sorry Jobst - we don't have "math" downunder either, we have "maths"
as in Pure Maths, Applied Maths. "math" is an Americanism.


That's fine. Only one with a stiff upper lip would create such an
abbreviation that defies pronunciation. I suppose as long as it
remains on the KBD it doesn't tangle the tongue. The essence of a
lisp is the mix of 'th" and 's'. To make 'maths' from 'mathematics'
is an excessive linguistic rigourosity. I see we are more fortunate
in the USA with a bit of realism and where we do our 'math' without
linguistic twisting of the tongue.

Jobst Brandt


Dear Jobst,

Perhaps we should drop that dreadful terminal "s"
and speak of the Mathematic Department? After all,
our fortunate, realistic children have led the
way--they do arithmetic instead of arithmetics.
When they grow up, let them study linguistic and
and physic in the art and science.

Wouldn't it have been easier to say oops, you
didn't know that "maths" is proper slang where
Brytysh bycyclysts named Smythe ryde on tyres?

Nothing looks sillier than a pedant trying
not to look ignorant--except, come to think
of it, a pack of other pedants gleefully piling
on top of him.

Adult, n. A mature individual whose slightest
lapse entitles everyone--including himself--to
behave as childishly as possible. One who no
longer enjoys the kindness and courtesy traditionally
extended to children.

Carl Fogel

P.S. As a minor linguistic aside, plurals in English
are historically troublesome.

Consider the classic cases of the pair of scissors
and the pair of pants. We avoid dealing with their
ambiguity by saying "gimme the scissors" or "hand
me my pants, dear."

The indefinite "the" and the innumerate possessive
"my" gracefully avoid the vexed question of whether
the scissors and pants are singular or plural.

Well-educated snots will crisply ask for "a scissors,"
loftily informing anyone who cares that the instrument
is singular. They then wonder why the snips are handed
to them point-first. They never ask for "a pants."

In Old English (not Chaucer's fairly readable Middle
English), the pants and scissors were no problem at
all. The world was "sensibly" divided into not singular
versus more than one, but into singular, dual, and
more than two.

They had words like "a" for things came one by one,
words like "those" for things that might come in droves,
and words in-between that we now lack for things like
pants, scissors, and portions of the human anatomy that
naturally come in pairs.

Like the British "maths," a singular-dual-plural system
is obviously wrong and reprehensible to us, but makes
sense to those who know no better.

The Old English also cared about gender and divided
almost everything into masculine and feminine.

This was too damned complicated, so English lost
almost all gender, just as today there is a growing
tendency among European youths to forgo the proper
masculine and feminine articles.

Only the strong survive, so most of our words have
been simplified and regularized. Our strongest words
are the most common verbs, used in most conversation.

Feeble modern verbs like bicycle are quite simple:
bicycle, bicycles, bicycled, and bicycling. There is
no "bicycleth," much to Jobst's relief (although
"Jobst's" is easier to type than to pronounce).

The strong verb in English is the hideous hodge-podge
"to be," which is conjugated as am, is, are, been,
being, was, and were, a completely nonsensical
progression explained by the fact that we once had
several forms of "to be" with different meanings
that all got mashed together in the continuing
bumper-car madness of linguistic evolution. (Consider
Spanish, where "ser" and "estar" both translate to
"to be," but have important differences obvious to
any child brought up in the language.)

C.F.

P.P.S. Double-dare ya' all to top this for linguistic
pedantry!

C.F.
  #64  
Old October 8th 03, 10:29 PM
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Default "The Stability of the Bicycle"

Carl Fogel writes:

P.P.S. Double-dare ya' all to top this for linguistic pedantry!


Excellent and entertaining.

Jobst Brandt

  #65  
Old October 8th 03, 11:07 PM
Bill Patterson
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I asked a simple question about the relative effect of the two.

Check the equations on my web site

http://www.calpoly.edu/~wpatters/

Most bikes have little moment of inertia on the front wheel. Therefore, the
torque
trasmitted up the steer tube is small. The primary torque coming up the
steering column is from the vertical normal force and sideward friction
force on the front wheel contact point. These forces generate a torque
acting through the trail vector that is then dot producted (?) with a vector
up the steer tube.

Motorcycles and bikes with heavy rims are exceptions.

In my opinion, stability is not a suitable design goal. No fighter aircarft
was designed to be stable. The airplane guys started "doing" stability when
they started flying instruments and didn't have good situational awareness.

You don't want a stable bike. You want a bike the responds properly to your
intentions.







  #66  
Old October 8th 03, 11:30 PM
Benjamin Lewis
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Default "The Stability of the Bicycle"

Simon Brooke wrote:

writes:

Simon Brooke writes:

Actually, this report
URL:
http://www.geocities.com/CollegePark...32/pyfair.html
contradicts Jobst. It says that


'He reversed the front fork to nullify the caster action, and he
fitted a counter-rotating wheel on the front fork to effectively
nullify or cancel out the gyroscopic effects. When he was
finished, he still found that the bicycle could still be balanced
and steered quite easily... These experiments effectively
disproved the hypothesis that gyroscopic motion was the primary
force responsible for balance in a bicycle...'


There is one of the glaring failures of this report. There is mention
of riding no-hands mixed in with being able to control the bicycle.
In the above paragraph, one might assume he meant riding no-hands, but
in fact that is impossible and was not the case. Therefore, it does
not conflict with what I have said.


On the contrary he is quoted as explicitly saying he rode no hands.
See for example URL: http://www.dclxvi.org/chunk/tech/trail/

'...he found it difficult (although not impossible) to ride with his
hands off of the handlebars ...'

Dr Jones article is cited as
Jones, David E.H., "The Stability of the Bicycle", Physics Today
(April 1970): 34-40

I have not read it myself.


Here's the relevant quote from the paper:

,----
| Gingerly, and with great trepidation, I tried the experiment --
| downhill, to avoid complicating the effort with pedalling. URB I is not
| an easy bicycle to ride "hands off" even with the front wheel static; it
| somehow lacks balance and responsiveness. In the disrotatory mode it was
| almost impossible and invited continual disaster, but it could, just, be
| done.
`----

--
Benjamin Lewis

Now is the time for all good men to come to.
-- Walt Kelly
  #68  
Old October 9th 03, 02:00 AM
John Dacey
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Default "The Stability of the Bicycle"

On Thu, 09 Oct 2003 00:05:16 GMT, Simon Brooke esquire, metapedant
wrote:

P.P.S. Double-dare ya' all to top this for linguistic
pedantry!


ITYMHM '_I_ _challenge_ _you_ to _better_ this for linguistic pedantry'.

The phrase 'you all' is a deprected colonial form; the 'all is
redundent and may be elided. 'Double-dare' is slang, and, worse,
vulgar.


Your spellchecker is broke.

"Quis custodiet ipsos custodes?" - Juvenal

-------------------------------
John Dacey
Business Cycles, Miami, Florida
http://www.businesscycles.com
Now in our twenty-first year.
Our catalog of track equipment: eighth year online
-------------------------------
  #69  
Old October 9th 03, 03:50 AM
Tim McNamara
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Default "The Stability of the Bicycle"

In article . net,
"Bill Patterson" wrote:

In my opinion, stability is not a suitable design goal. No fighter
aircarft was designed to be stable. The airplane guys started
"doing" stability when they started flying instruments and didn't
have good situational awareness.

You don't want a stable bike. You want a bike the responds properly
to your intentions.


"Properly" in this case is probably what most of us are thinking of as
"stable."

In Jones's URB experiments, he was able to make a bike so stable that
it was effectively unrideable- indeed it was so stable that it was
self-balancing. The video that was broadcast in the two-part PBS show
called "The Bicycle" about 10 years ago was very entertaining, with
the riderless bike coasting away down a hill quite nicely. Conversely
it's possible to make a bike so "responsive" that it's unrideable.

Bikes for different purposes tend to need different stability
characteristics. A "crit" bike tends to be very responsive, but after
riding it 250 km it would be unpleasant. A bike designed for brevets
and similar ultra-long rides will be very stable, to allow it to be
ridden in a straight line while very fatigued, but wouldn't be much
fun in a crit.

My most stable bike is my track bike, despite the 75 degree head
angle. It can be ridden no-handed very easily for long distances,
around corners, up and down hill, over bumps, etc. That makes sense,
since track bikes are effectively ridden in a straight line around a
velodrome, thanks to the banking. My least stable bike is a mid-80's
Japanese bike with a 73 degree head angle and a bit too much fork
offset, reducing trail just a bit too much.
 




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