"The Stability of the Bicycle"

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.


--
(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

writes:

Simon Brooke 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:

[snip]

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.

No need to belabor what is self evident. We have all parked a bicycle
either leaning against a wall or on a kick-stand and seen that the
front wheel turns to the side to which the bicycle leans. This is not
what steers the bicycle in this exercise.

When walking a bicycle, holding it by the saddle, lean angles are
trivially small and cause steering by gyroscopic action, the test for
which you have apparently not done.

I have now done, and reported on, both the experiments you suggest. In
neither experiment was I able to reproduce your reported results. As
I've said, I'm quite happy to repeat both on camera and post Quicktime
movies so that everyone can verify my results. I suggest you repeat
your own experiments.

--
(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

wrote in message
...
Simon Brooke writes:

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.

Well don't just sit there and fret about it, try it. Take the wheel
out and turn it.

What would that tell you about rake/trail/lean ?

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

In article ,
wrote:


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

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.

plus, we got them cranksets here too.

Simon Brooke writes:

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.

Well don't just sit there and fret about it, try it. Take the
wheel out and turn it.

I've done that often enough. I'm aware of the degree of gyroscopic
force you can get from a fast spinning wheel;

Well try spinning it slowly. You keep insisting that it requires a
lot of speed. It doesn't. Try spinning the wheel ad slower and
slower speeds (vertically as in a bicycle), holding the wheel by only
one end of the axle. You will note that the slower the wheel turns
the faster it will precess (steering motion).

all I'm questioning is how much this force contributes to balancing
a bike, and whether it's a significant component (particularly at
low speeds). The fact that bikes lean steer is easily verified; the
extent to which this is gyro-assisted is less easily assessed.

Whoa! That's a dodge. We have never mentioned that the bicycle is
held upright by gyroscopic forces, only that it can be steered that
way. The basis for all this is in the FAQ because people of your
persuasion pop up regularly here.

http://draco.acs.uci.edu/rbfaq/FAQ/9.35.html

Jobst Brandt

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.

Now, I have no way immediately of assessing whether Jobst's claim or
the report given above should be given more credence. But lean
steer works for a number of other 'vehicles' which have no
gyroscopic effects. Snowboarders manage just fine no hands, as do
surfers. Furthermore, on both these platforms control increases
with speed. Thus gyroscopic effects are not _required_ to account
for the ability to ride a bike no hands.

You are grasping at straws. The Skibob example is given in the FAQ,
surfing, ice skating and skiing are a different matter entirely and
fall into the category of running, where humans balance by moving the
ground contact point to be plumb with the body. The surfboard and
snowboard can be steered by canting the board and the shifting of
weight.

Jobst Brandt

Simon Brooke 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.

Held in both hands, axle horizontal, a wheel at 1Hz steers easily and
rapidly when the axle is tilted slightly to either side. This is the
effect one gets when wheeling the bicycle by the saddle. To see the
effect more dramatically, hanging the wheel by one end of the
horizontal axle while it is spinning shows that the precession speed
increases with decreasing rotational velocity. This experiment shows
that tilting the wheel easily steers it as in riding no-hands.

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 think that depends more on rider skill than whether or not there is
a gyroscopic steering effect in riding the bicycle no-hands, whether
on the bicycle or walking next to it.

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.

I don't see what persuasion you are getting for your point of view,
with all experimental evidence pointing the other way. By the way, do
you ride no-hands?

Jobst Brandt

Why is it that I could lean the bike further when turning with my hands on
the
handlebars than I could with no hands? fear?
I've seen some Chinese Acrobats lean their bike way over with no hands.

btw: I did your experiment of riding with no hands from the top of Sand Hill
Rd. East.
No shimmy, so it must be self induced.
-tom


wrote in message
...
'

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.

Simon Brooke wrote:

David Damerell writes:

"jim beam" wrote:
Benjamin Lewis:
"jim beam"
as Jobst has claimed.
that's proof?

There's a neat piece of selective quoting. What this should read is;

old high school physics footage of a bike being ridden with a counter
gyroscopic wheelset. works just fine.
And is reportedly "almost impossible" to ride no-hands, as Jobst has
claimed.

I.e., the behaviour of this bike substantiates Jobst's claim.

With respect, that behaviour of a counter-gyroscopic bike is reported
in Jobst's claim. Thus it can't either substantiate or refute it. What
could substantiate or refute it is an independent report from someone
who had either seen the film (in which case they could confirm what
was said on the film) or had ridden the bike (in which case they
could confirm the behaviour of the bike).

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.

--
Benjamin Lewis

Never underestimate the bandwidth of a station wagon full of tapes.
-- Dr. Warren Jackson, Director, UTCS

wrote in message
...
Simon Brooke writes:

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.

Well don't just sit there and fret about it, try it. Take the
wheel out and turn it.

I've done that often enough. I'm aware of the degree of gyroscopic
force you can get from a fast spinning wheel;

Well try spinning it slowly. You keep insisting that it requires a
lot of speed. It doesn't. Try spinning the wheel ad slower and
slower speeds (vertically as in a bicycle), holding the wheel by only
one end of the axle. You will note that the slower the wheel turns
the faster it will precess (steering motion).

The rate of precession increases as the wheel turns slower because it
has less momentum and because the torque on the axle (the weight of the
hanging wheel) remains the same. By this you imply that precession is
greater with a slower turning wheel but when wheeling a bicycle slowly,
precession is less because the torque inducing it by leaning the wheel
is less and eventually becomes overshadowed.

Phil Holman