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"The Stability of the Bicycle"



 
 
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  #71  
Old October 9th 03, 06:43 AM
A Muzi
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Default "The Stability of the Bicycle"

I asked a simple question about the relative effect of the two.

Bill Patterson wrote:
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.



I agree.
Your comments caught my eye with the word "stable" because I
had never considered that a virtue. This year, I was asked
several times by customers for a "stable" bicycle, including
a gentleman who specified that as his prime motivation for
buying a custom touring frame. I am at a loss to explain this.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

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  #72  
Old October 9th 03, 08:29 AM
W K
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Default "The Stability of the Bicycle"


wrote in message
...

When walking a bicycle, holding it by the saddle, lean angles are
trivially small and cause steering by gyroscopic action


I don't see how you get that conclusion from the below.

the test for
which you have apparently not done. Take the wheel out of the
bicycle, turn it at "walking speed" and tilt it to the left and right
in your hands. You will notice a quick and relatively forceful
steering response.


Yep.

It is this force that allows the bicycle to be
steered by slight lean angles


Very slight indeed.

I have an alternative experiment I'd like you to comment on:
Take whole bike, put back wheel on a brick so it can be held horizontally.

Tip bike slightly to one side, and see the way the steering goes.

I did this for:
a) wheels stationary - steering flops to one side.
b) wheel going at 20 kph - could not see any difference.
c) wheel going at 20kph BACKWARDS - very slight effect of steering going
opposite direction. With several attempts I only saw this happen once, and
it was soon overcome by a similar "flop" to (a).

No Maths for the above, but it shows the gyroscope effect is easily swamped
by other effects.


  #73  
Old October 9th 03, 10:03 AM
DejaVU
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Default "The Stability of the Bicycle"


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


followed by....

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.
`----


havn't you guys given thought to the fact that the forks were
reversed to remove the caster action? this would make it a total
bitch to ride no-hands for sure.

to my mind the gyro forces don't even come close to the caster action
forces, at any speed. I balance (and steer) my bicycle by moving the
contact point around to change the top heavy weight distribution.
I'm sure I do this. To go left I first steer right, sort of a
wobble, to move the contact patch to the right so the system is
unbalanced, then I steer left to counter that force, and by
countering it only anough to prevent falling, I go round a corner.
to straighten up again one steers MORE left to get the wheels back
under your weight and balance the system. I don't see where gyro
forces come in at all, EXCEPT when no-hands riding, MAYBE. I believe
that is all leansteer/caster angle acting. it is harder at low
speed, but if you lean forward you'll find it easier, this increases
caster action. go try it


swarf, steam and wind

--
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  #74  
Old October 9th 03, 10:05 AM
DejaVU
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Default "The Stability of the Bicycle"

Benjamin Lewis scribed in
:


You misunderstand me. The bicycle with a "counter gyroscopic
wheelset" has been tried by someone other than Jobst (I don't
remember the reference, but someone posted a link to an academic
paper the other day), and found by this person to be almost
impossible to ride no hands, as Jobst has claimed.


but it was quoted that the forks were reversed to remove the caster
action. that alone would make it very scary to no-hands ride.
in that context the gyro effects are meaningless

swarf, steam and wind

--
David Forsyth -:- the email address is real /"\
http://terrapin.ru.ac.za/~iwdf/welcome.html \ /
ASCII Ribbon campaign against HTML E-Mail - - - - - - - X
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PLEASE pretend you don't know me.
  #75  
Old October 9th 03, 10:16 AM
DejaVU
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Default "The Stability of the Bicycle"

Bill Patterson scribed in
. net:

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.


yup, Sopwith Pup was a total bitch to fly for this reason.

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


yes, for some things.

I used to have a Peugot bike. I called it a 'cruiser'. The head
angle, in fact the whole frame, was stable in the extreme, much more
so than the 10 speed 'racer' I'd had before (stolen). perfect for
ambling along or ordinary commuting (I rode it to school for years),
maybe touring with panniers. nice bike, no surprises

my current bike, a Nishiki 'Graffiti' MTB, is much less stable, has a
higher head angle etc. tricky to no hands at low speed unless one
leans forward to increase the caster forces. I have slicks on it,
the knobblies I wore out were worse. But I'm happy with it, as it is
responsive.
  #76  
Old October 9th 03, 11:05 AM
Simon Brooke
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Default "The Stability of the Bicycle"

DejaVU writes:

Benjamin Lewis scribed in
:

You misunderstand me. The bicycle with a "counter gyroscopic
wheelset" has been tried by someone other than Jobst (I don't
remember the reference, but someone posted a link to an academic
paper the other day), and found by this person to be almost
impossible to ride no hands, as Jobst has claimed.


but it was quoted that the forks were reversed to remove the caster
action. that alone would make it very scary to no-hands ride.
in that context the gyro effects are meaningless


Just so. And yet is was 'very difficult but not impossible' to ride no
hands.

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

;; in faecibus sapiens rheum propagabit
  #77  
Old October 9th 03, 11:05 AM
Simon Brooke
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Default "The Stability of the Bicycle"

John Dacey writes:

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.


Touche!

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

;; in faecibus sapiens rheum propagabit
  #79  
Old October 9th 03, 05:34 PM
Benjamin Lewis
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Default "The Stability of the Bicycle"

Simon Brooke wrote:

DejaVU writes:

Benjamin Lewis scribed in
:

You misunderstand me. The bicycle with a "counter gyroscopic
wheelset" has been tried by someone other than Jobst (I don't
remember the reference, but someone posted a link to an academic
paper the other day), and found by this person to be almost
impossible to ride no hands, as Jobst has claimed.


but it was quoted that the forks were reversed to remove the caster
action. that alone would make it very scary to no-hands ride.
in that context the gyro effects are meaningless


Just so.


Says the man who hasn't read the article.

And yet is was 'very difficult but not impossible' to ride no hands.


Sorry, it was a different bicycle on which the forks were reversed. This
bicycle had normal forks, and yet was nearly impossible to ride no hands
due to the lack of gyroscopic effects.

http://tinyurl.com/pswa

--
Benjamin Lewis

Everything that can be invented has been invented.
-- Charles Duell, Director of U.S. Patent Office, 1899
  #80  
Old October 9th 03, 07:40 PM
Phil Holman
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Default "The Stability of the Bicycle"

"W K" wrote in message ...
wrote in message
...

When walking a bicycle, holding it by the saddle, lean angles are
trivially small and cause steering by gyroscopic action


I don't see how you get that conclusion from the below.

the test for
which you have apparently not done. Take the wheel out of the
bicycle, turn it at "walking speed" and tilt it to the left and right
in your hands. You will notice a quick and relatively forceful
steering response.


Yep.

It is this force that allows the bicycle to be
steered by slight lean angles


Very slight indeed.

I have an alternative experiment I'd like you to comment on:
Take whole bike, put back wheel on a brick so it can be held horizontally.

Tip bike slightly to one side, and see the way the steering goes.

I did this for:
a) wheels stationary - steering flops to one side.
b) wheel going at 20 kph - could not see any difference.
c) wheel going at 20kph BACKWARDS - very slight effect of steering going
opposite direction. With several attempts I only saw this happen once, and
it was soon overcome by a similar "flop" to (a).

No Maths for the above, but it shows the gyroscope effect is easily swamped
by other effects.


I'm not picturing what you did exactly but you bring up an interesting
point. The front wheel turning backwards. If a bicycle is wheeled
backwards, and I assume according to Jobst's hypothesis, the
gyroscopic effect should steer the front wheel in the opposite
direction. I haven't done the test yet but for some, it may bring
clarity to the situation as to which is the dominant force......or
not.

Phil Holman
 




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