A Cycling & bikes forum. CycleBanter.com

Go Back   Home » CycleBanter.com forum » rec.bicycles » Techniques
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

"The Stability of the Bicycle"



 
 
Thread Tools Display Modes
  #21  
Old October 7th 03, 05:55 AM
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

Peter Rathman writes:

Take the wheel out, spin it in you hands and try to tilt it to the
left or right and note the force of the steering action. This
should convince you of its effect.


please explain. gyro reaction is _90 degrees to the applied
force_. i.e. my front wheel, spinning "forwards" tries to tilt top
rightwards when turned to the left. you seem to be implying that
gyro recation is responsible for banking the bike to the left when
steered left.


No, when you wheel the bike along holding onto the seat you steer by
banking the bike and the turn is a reaction to the bank. Banking
the bike to the left will tend to initiate a turn to the left. But
the gyroscopic force is quite small when the wheel is spun at only
walking speed and the geometry of the bike also results in the wheel
turning left in response to a left bank (even when the wheel isn't
rotating). I'd have to try this with a counter-rotating second
front wheel (like on URB I) before concluding which is the dominant
effect.


That is why I suggest the spinning wheel in hand experiment. The
steering forces are not small and are sufficient at casual walking
speed to steer the bicycle. That the bicycle does not steer when
stationary shows that effect as well. TO make the bicycle steer
merely from rake and trail takes a large lean angle and does not
accomplish the same effect. You don't need any esoteric URB's to test
this with your own mount although this may not sound as scientifically
complex, it demonstrates the effects strikingly.

Jobst Brandt

Ads
  #22  
Old October 7th 03, 06:33 AM
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

anonymous writes:

Take the wheel out, spin it in you hands and try to tilt it to the
left or right and note the force of the steering action. This
should convince you of its effect. You don't need to solve
differential equations.


OK, but envision a system without any rotating elements. Substitute
a runner or blade shaped essentially the same as the bottom of a
wheel and substitute sliding for rolling. Such a device would still
have a turning capability without the existence of any gyroscopic
effect.


You don't have to go to other devices to see that when the wheel is
not rotating the self steering does not work. For it to work on a non
rotating wheel, the bicycle must be leaned significantly for front
wheel trail to have any effect.

Don't! There is more to be gained by intelligent observation of
natural phenomena.


You mean it's OK to be able to "feel" something even if you can't
prove it exists mathematically?


You don't have to call it "feel". We are talking about physical
effects that either do or do not occur. Their presence is
demonstrable without delving into jargon and mathematical proofs.

Jobst Brandt

  #23  
Old October 7th 03, 06:55 AM
Peter
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

wrote:

Peter Rathman writes:


Take the wheel out, spin it in you hands and try to tilt it to the
left or right and note the force of the steering action. This
should convince you of its effect.



please explain. gyro reaction is _90 degrees to the applied
force_. i.e. my front wheel, spinning "forwards" tries to tilt top
rightwards when turned to the left. you seem to be implying that
gyro recation is responsible for banking the bike to the left when
steered left.



No, when you wheel the bike along holding onto the seat you steer by
banking the bike and the turn is a reaction to the bank. Banking
the bike to the left will tend to initiate a turn to the left. But
the gyroscopic force is quite small when the wheel is spun at only
walking speed and the geometry of the bike also results in the wheel
turning left in response to a left bank (even when the wheel isn't
rotating). I'd have to try this with a counter-rotating second
front wheel (like on URB I) before concluding which is the dominant
effect.



That is why I suggest the spinning wheel in hand experiment.


Which I had just done before posting the above.

The
steering forces are not small and are sufficient at casual walking
speed to steer the bicycle.


I walked along with the wheel on the ground and then picked it up so it
continued to rotate at the same speed (about 2 - 3 mph). With that rate of
rotation I found the gyroscopic forces to be barely perceptible when I
gently leaned the wheel over while holding it in my hands.

That the bicycle does not steer when
stationary shows that effect as well.


? The front wheel certainly does turn to the side if the bike is leaned
while stationary. It does take a larger lean angle than when moving, but
that would be expected merely from frictional considerations and doesn't
prove that gyroscopic forces are needed.

TO make the bicycle steer
merely from rake and trail takes a large lean angle and does not
accomplish the same effect. You don't need any esoteric URB's to test
this with your own mount although this may not sound as scientifically
complex, it demonstrates the effects strikingly.


My observations are that either effect could explain the ability to steer a
bike by making it lean by small amounts while walking so distinguishing
between them would require either constructing a frame/fork with a
different rake/trail geometry to eliminate one effect or canceling the
gyroscopic force to eliminate the other.

  #25  
Old October 7th 03, 10:35 AM
Simon Brooke
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

Peter writes:

jim beam wrote:

Take the wheel out, spin it in you hands and try to tilt it to the
left or right and note the force of the steering action. This should
convince you of its effect.

please explain. gyro reaction is _90 degrees to the applied
force_. i.e. my front wheel, spinning "forwards" tries to tilt top
rightwards when turned to the left. you seem to be implying that
gyro recation is responsible for banking the bike to the left when
steered left.


No, when you wheel the bike along holding onto the seat you steer by
banking the bike and the turn is a reaction to the bank. Banking the
bike to the left will tend to initiate a turn to the left. But the
gyroscopic force is quite small when the wheel is spun at only walking
speed and the geometry of the bike also results in the wheel turning
left in response to a left bank (even when the wheel isn't
rotating).


Well, just so. I agree that you can get strong gyroscopic effects with
a fast rotating wheel, but I'm completely unpersuaded that they are
significant at walking speed. So, again, has anyone done the maths?

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

[ This .sig intentionally left blank ]
  #26  
Old October 7th 03, 10:35 AM
Simon Brooke
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

writes:

That the bicycle does not steer when
stationary shows that effect as well. TO make the bicycle steer
merely from rake and trail takes a large lean angle and does not
accomplish the same effect.


OK, I have just been out to the bike shed and carried out an empirical
experiment; and this is just false. My observations are, when stationary:

(i) On rougher surface (grass), greater lean angles are required before a
steering effect is noticed as compared to smoother surfaces (tiled
floor).

(ii) On tyres with a larger contact patch (mountain bike), greater lean
angles are required before a steering effect is noticed as compared to
smaller contact patch (road bike).

(iii) All bikes on all surfaces showed steering effect on lean.

(iv) Road bike on tiled floor showed to within the limits of
observational measurement as much steering effect on the same amount
of lean when stationary as when moving.

(v) By contrast, a mountain bike on grass had to be leant to a
considerable angle to show any steering effect when stationary, and
when the steering effect did occur it occured in jerky movements
through considerable angles.

From this I conclude that the resistance to steering when stationary
is as much due to friction at the contact patch as anything else (and,
lets face it, tyres are designed to generate the maximum possible
friction at the contact patch).

I'm quite prepared to repeat the experiment on camera an post a
quicktime movie. But it's a very simple experiment and I'm sure
everyone else can repeat it too.

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

[ This .sig intentionally left blank ]
  #28  
Old October 7th 03, 11:59 AM
W K
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"


wrote in message
...
Jim Beam writes:

Take the wheel out, spin it in you hands and try to tilt it to the
left or right and note the force of the steering action. This
should convince you of its effect.


please explain. gyro reaction is _90 degrees to the applied force_.
i.e. my front wheel, spinning "forwards" tries to tilt top
rightwards when turned to the left. you seem to be implying that
gyro recation is responsible for banking the bike to the left when
steered left.


Not at all. I suggest that the wheel spinning forward steers to the
left when tilted to the left and to the right when tilted to the
right.


I wouldn't disagree with the above.

This is the means by which the bicycle steers when walking the
bike while held by the saddle and also what enables it to be ridden
no-hands.


What is the relative contribution of the different effects - ie to what
degree is the above more important than the effects of rake and trail - at
different speeds and with the addition of the rider to the whole system.


  #29  
Old October 7th 03, 03:05 PM
Simon Brooke
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

"W K" writes:

What is the relative contribution of the different effects - ie to what
degree is the above more important than the effects of rake and trail - at
different speeds and with the addition of the rider to the whole system.


As a child I rode one winter a bicycle which had a normal rear wheel
but had part of an old ski bolted onto the front forks in place of the
front wheel. It was good fun to use and I don't remember it handling
noticably differently from a normal bike. This is a long time
ago and I could be wrong, but again it's easy enough to verify.

This isn't to deny that gyroscopic effects play some part, nor that
the influence of gyroscopic effects increases with speed; but without
some maths I'm skeptical about their being significant as compared to
lean.

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

;; how did we conclude that a ****ing cartoon mouse is deserving
;; of 90+ years of protection, but a cure for cancer, only 14?
-- user 'Tackhead', in /. discussion of copyright law, 22/05/02
  #30  
Old October 7th 03, 03:40 PM
Phil Holman
external usenet poster
 
Posts: n/a
Default "The Stability of the Bicycle"

"W K" wrote in message ...
wrote in message
...
Jim Beam writes:

Take the wheel out, spin it in you hands and try to tilt it to the
left or right and note the force of the steering action. This
should convince you of its effect.


please explain. gyro reaction is _90 degrees to the applied force_.
i.e. my front wheel, spinning "forwards" tries to tilt top
rightwards when turned to the left. you seem to be implying that
gyro recation is responsible for banking the bike to the left when
steered left.


Not at all. I suggest that the wheel spinning forward steers to the
left when tilted to the left and to the right when tilted to the
right.


I wouldn't disagree with the above.

This is the means by which the bicycle steers when walking the
bike while held by the saddle and also what enables it to be ridden
no-hands.


What is the relative contribution of the different effects - ie to what
degree is the above more important than the effects of rake and trail - at
different speeds and with the addition of the rider to the whole system.


The mass imbalance is a constant for a given bicycle and the speed at
which it will impart steering action is dependent on the lean angle
and is easily observable with a stationary bicycle. Gyroscopic
precession is dependent on rotation rate of the wheel, the faster the
wheel rotates the higher the torque required to lean the wheel for a
give rate of precession. At walking speed (1/2 rev/sec) the difference
in torque between leaning this and a stationary wheel will be the
amount of torque that causes the wheel to turn (precess). It will be
small and likely doesn't even overcome the trail effect of keeping the
wheel pointed straight ahead. Rider weight adds more tire scrub
effects which are small but riding no hands at low speeds is almost
impossible due to insufficient gyroscopic forces. It's not until the
bicycle is going ~15mph does no hands riding become feasible for the
ordinary rider. Gyroscopic forces being large enough to impart
adequate self steering.

Phil Holman
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
A song for Carla John Harlow Mountain Biking 3 May 10th 04 02:29 PM
Those bicycle builders big mistake! Garrison Hilliard General 30 December 23rd 03 07:03 AM
Reports from Sweden Garry Jones General 17 October 14th 03 05:23 PM
Reports from Sweden Garry Jones Social Issues 14 October 14th 03 05:23 PM


All times are GMT +1. The time now is 08:27 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 CycleBanter.com.
The comments are property of their posters.