Re: Fell off

Simon Brooke said:

You should read David Jones paper on the Unrideable Bicycle (_The
Stability of the Bicycle_, Physics Today 23, 34-36); you would find it
instructive. There's a PDF on the net somewhere but I've lost the link.

http://socrates.berkeley.edu/~fajans/Teaching/MoreBikeFiles/JonesBikeBW.pdf

..... or so you posted this August.

Mike

in message
<[email hidden]>, Mike

Causer (') said:

Simon Brooke said:

You should read David Jones paper on the Unrideable Bicycle (_The
Stability of the Bicycle_, Physics Today 23, 34-36); you would find
it instructive. There's a PDF on the net somewhere but I've lost the
link.

http://socrates.berkeley.edu/~fajans/Teaching/MoreBikeFiles/JonesBikeBW.pdf

Quoted message said:

.... or so you posted this August.

Thanks, yes. I knew somebody would remember.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

my other car is #<Subr-Car: #5d480>
;; This joke is not funny in emacs.

Simon Brooke said:

Thanks, yes. I knew somebody would remember.

In truth, Google remembered for me ......

.... up till today I'd just used the report of Daedelus' findings in
D.G. Wilson's "Bicycling Science" 3rd Ed.

Mike

Simon Brooke said:

in message
<[email hidden]>, Mike

Causer (') said:

Simon Brooke said:

You should read David Jones paper on the Unrideable Bicycle (_The
Stability of the Bicycle_, Physics Today 23, 34-36); you would find
it instructive. There's a PDF on the net somewhere but I've lost the
link.

http://socrates.berkeley.edu/~fajans/Teaching/MoreBikeFiles/JonesBikeBW.pdf

Quoted message said:

.... or so you posted this August.

Thanks, yes. I knew somebody would remember.

Now that we've sorted whether you turn left or right to turn left, can
we move on to whether the wheel hangs or rests on the spokes please.

Only joking.

Simon Brooke said:

in message <[email hidden]>, James Annan

(') said:

Your logic is broken, I'll merely point out that the countersteering
is NOT "in effect a short turn in the other direction", it is in fact
a loss of balance in which the _bicycle_ (contact patch) moves to one
side while the _rider_ is left behind. If you did it for more than a
brief moment, you would fall off, not turn.

I suggest you try riding a bicycle. You will find that if you lean the
bicycle to one side, it will turn to that side, without any need for
any other steering input. If you lean your body to one side, thus
moving your centre of gravity, then the bike will naturally lean to the
other side, and thus you can easily initiate a turn in either
direction.

I agree that it is possible to tip the bicycle to one side while riding
along no-hands. I suggest you consider what happens when an
intantaneously balanced rider does this. Since there is no external
lateral force (I assume from your snipping of my question on this point
that you do not dispute it) then for the bicycle to move a little to the
left, the rider's CoG must move a rather smaller distance to the right.

So we have the bicycle marginally to the left of the rider, and turning
further to the left.

In the immortal words of David Vine,

"What happens next"?

Quoted message said:

You should read David Jones paper on the Unrideable Bicycle (_The
Stability of the Bicycle_, Physics Today 23, 34-36); you would find it
instructive. There's a PDF on the net somewhere but I've lost the link.

You should try not to be so patronising from a position of ignorance.
You made an [censored] of yourself only a couple of weeks ago when trying to
pontificate about mathematical concepts that you did not understand. I
doubt anyone needs the lesson reinforced. I certainly don't.

I'll repeat the question from my previous email:

Quoted message said:

Quoted message said:

One can initiate a
turn by any means which moves the CoG away from vertically above the
track. Sudden body movements exploiting inertia do this easily - so
easily, in fact, that it's instinctive.

Can you describe such a movement, with particular reference to the source of the external lateral force that is required to move the CoG to one side? You might like to think of it as a torque around the wheel contact patch since the motion can also be viewed as a rotation about that point. (This takes the contact point out of the picture entirely.)

Once you accept that (for a balanced rider, eg CoG vertically above tyre
contact patch and riding straight ahead) there are no external forces
that can move the combined CoG of bike and rider to one side, it is an
immediate corollary that the only way to turn to the right, is to make
the contact patch move to the left relative to the CoG. That is all that
"countersteering" means.

James
--
If I have seen further than others, it is
by treading on the toes of giants.
http://www.ne.jp/asahi/julesandjames/home/

James Annan said:

Once you accept that (for a balanced rider, eg CoG vertically above tyre
contact patch and riding straight ahead) there are no external forces
that can move the combined CoG of bike and rider to one side, it is an
immediate corollary that the only way to turn to the right, is to make
the contact patch move to the left relative to the CoG. That is all that
"countersteering" means.

I'm sure that I will regret getting involved in this one but...

Can't the balanced rider just lean from the hips. I'm writing this while
leaning slightly to the right in my chair (In fact, I look a prat
because I'm concentrating on the screen while randomly leaning from side
to side). I see no reason why this cannot be done on a bike and it would
then move the CoG away from the contact patch.

Jon

Not Responding said:

Now that we've sorted whether you turn left or right to turn left, can
we move on to whether the wheel hangs or rests on the spokes please.

Given the ominous creaks from Igor's back wheel, I think even the spokes
are arguing about that one.

Must threaten it with a spoke key..

...d

in message <[email hidden]>, James Annan

(') said:

Simon Brooke said:

in message <[email hidden]>, James Annan

(') said:

Your logic is broken, I'll merely point out that the countersteering
is NOT "in effect a short turn in the other direction", it is in fact
a loss of balance in which the _bicycle_ (contact patch) moves to one
side while the _rider_ is left behind. If you did it for more than a
brief moment, you would fall off, not turn.

I suggest you try riding a bicycle. You will find that if you lean
the bicycle to one side, it will turn to that side, without any need
for any other steering input. If you lean your body to one side, thus
moving your centre of gravity, then the bike will naturally lean to
the other side, and thus you can easily initiate a turn in either
direction.

I agree that it is possible to tip the bicycle to one side while
riding along no-hands. I suggest you consider what happens when an
intantaneously balanced rider does this. Since there is no external
lateral force (I assume from your snipping of my question on this
point that you do not dispute it) then for the bicycle to move a
little to the left, the rider's CoG must move a rather smaller
distance to the right.

So we have the bicycle marginally to the left of the rider, and
turning further to the left.

In the immortal words of David Vine,

"What happens next"?

You adjust your balance and carry on normally. As to how you do this,
see below.

Quoted message said:

Quoted message said:

You should read David Jones paper on the Unrideable Bicycle (_The
Stability of the Bicycle_, Physics Today 23, 34-36); you would find
it instructive. There's a PDF on the net somewhere but I've lost the
link.

You should try not to be so patronising from a position of ignorance.

And he himself has said it, so it must be to his credit...

Quoted message said:

I'll repeat the question from my previous email:

Quoted message said:

Quoted message said:

One can initiate a
turn by any means which moves the CoG away from vertically above the
track. Sudden body movements exploiting inertia do this easily - so
easily, in fact, that it's instinctive.

Can you describe such a movement, with particular reference to the
source of the external lateral force that is required to move the CoG
to one side? You might like to think of it as a torque around the
wheel contact patch since the motion can also be viewed as a rotation
about that point. (This takes the contact point out of the picture
entirely.)

Certainly. The issue is entirely in the rapidity of acceleration and
deceleration of body movement, exploiting inertia. If it were not
possible to adjust balance in this way, riding a unicycle, for
instance, or walking on a tightrope, would be impossible. Yet they are
not. If it can be done on a tightrope, why is it impossible on a
bicycle?

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
Ye hypocrites! are these your pranks? To murder men and give God thanks?
Desist, for shame! Proceed no further: God won't accept your thanks for
murther
-- Roburt Burns, 'Thanksgiving For a National Victory'

in message <[email hidden]>, Jon Senior

jon_AT_restlesslemon_DOT_co_DOT_uk ('') said:

James Annan said:

Once you accept that (for a balanced rider, eg CoG vertically above
tyre contact patch and riding straight ahead) there are no external
forces that can move the combined CoG of bike and rider to one side,
it is an immediate corollary that the only way to turn to the right,
is to make the contact patch move to the left relative to the CoG.
That is all that "countersteering" means.

I'm sure that I will regret getting involved in this one but...

Can't the balanced rider just lean from the hips. I'm writing this
while leaning slightly to the right in my chair (In fact, I look a
prat because I'm concentrating on the screen while randomly leaning
from side to side). I see no reason why this cannot be done on a bike
and it would then move the CoG away from the contact patch.

Err, no it wouldn't. James is right about that. Provided it is done
slowly and smoothly, as you lean left, the bike leans right, keeping
the CoG more or less in the same place WRT the track. Try it when
you're riding no hands some time: this is one method by which you can
initiate turns (and, to be honest, I don't know of any other when
riding no hands).

Imagine standing on a tightrope. If you move your upper body slowly to
the left, your hips must move right. You can do this just by standing
on a line on the floor. The reason is that your only contact with the
world is the line, and, as James rightly points out, you have no
purchase or leverage to rotate your mass around that line.

The line or tightrope has some of the physics of a bike. On a bike, the
line is the track. However, on a bike, unlike a tightrope, the line can
be moved WRT the mass, by steering.

However, while we're on this subject, a suggestion for James. Stand on a
line on the floor, or the edge of a plank, or some similar object, one
foot in front of the other. Stand as still as you can. After a time you
will inevitably begin to fall to one side or the other. What
instinctive body movements do you make to correct your balance?

I think you will find that you make jerky movements of your shoulders
and arms. I think you will find that, some of the time at least, the
inertia from these jerky movements is sufficient to correct your
balance. If so, you must concede that this instinctive exploitation of
inertia gives you sufficient torque around the line to actually move
your centre of gravity. And if it works standing on a line, why can it
not work on a bicycle?

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

[ This mind intentionally left blank ]

in message <[email hidden]>, [Not

Responding (') said:

Now that we've sorted whether you turn left or right to turn left, can
we move on to whether the wheel hangs or rests on the spokes please.

I'm not going to hang around for that. I couldn't stand it...

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
Das Internet is nicht fuer gefingerclicken und giffengrabben... Ist
nicht fuer gewerken bei das dumpkopfen. Das mausklicken sichtseeren
keepen das bandwit-spewin hans in das pockets muss; relaxen und
watchen das cursorblinken. -- quoted from the jargon file

Simon Brooke said:

The line or tightrope has some of the physics of a bike. On a bike, the
line is the track. However, on a bike, unlike a tightrope, the line can
be moved WRT the mass, by steering.

That's bass-ackwards, of course. The tightrope can (and does) move
sideways under the performer. Look at those two brackets, and imagine
them to be a view of the performer from the rear. The left bracket has
the feet to the right of the CoG, and vice-versa. The bicycle contact
patch can only move sideways if the bicycle is steered to the side.

Quoted message said:

I think you will find that you make jerky movements of your shoulders
and arms. I think you will find that, some of the time at least, the
inertia from these jerky movements is sufficient to correct your
balance. If so, you must concede that this instinctive exploitation of
inertia gives you sufficient torque around the line to actually move
your centre of gravity. And if it works standing on a line, why can it
not work on a bicycle?

Well, standing on a single foot is not much problem for someone with
decent balance - it provides a platform several inches across and
twisting one's ankle can shift the effective pressure point from one
side to the other, giving a fair bit of wobble room before one risks
overbalancing. As the support gets narrower, it gets much harder, until
one (well, me at least) can only resort to increasingly desperate and
wild waving around of the arms. This can generate small temporary
torques, but has little to do with normal bike riding (even hands off)
and only prolongs the inevitable for a few seconds.

If you think you can control your balance a bicycle by this method, then
you should also be able to ride one in which the fork is locked straight
ahead. A few circus performers might be able to manage it, but 99.9% of
riders certainly cannot, and it has nothing to do with normal riding.

James
--
If I have seen further than others, it is
by treading on the toes of giants.
http://www.ne.jp/asahi/julesandjames/home/

Simon Brooke said:

Quoted message said:

So we have the bicycle marginally to the left of the rider, and
turning further to the left.

In the immortal words of David Vine,

"What happens next"?

You adjust your balance and carry on normally. As to how you do this,
see below.

Quoted message said:

Certainly. The issue is entirely in the rapidity of acceleration and
deceleration of body movement, exploiting inertia. If it were not
possible to adjust balance in this way, riding a unicycle, for
instance, or walking on a tightrope, would be impossible. Yet they are
not. If it can be done on a tightrope, why is it impossible on a
bicycle?

As I've already mentioned, the tightrope moves laterally under the
performer. This is also a trick that takes quite some skill (I doubt
many would go to the circus just to see a normal cyclist riding along).
A unicycle is also moved under the rider, in the fore-aft plane as well
as from side to side. The relevance of that to your point is not clear,
but then again, your point is not clear in itself.

Now, back to the cyclist. Assume this time he is not a circus performer.
How does he apply sufficient torque to himself to move himself bodily
from one side to the other of the contact patch. If you believe he can
do this, do you also believe he can ride a bicycle with the forks locked
straight ahead? If not, why not? Surely the same "adjust your balance
annd carry on normally" trick should work there too, shouldn't it?

James
--
If I have seen further than others, it is
by treading on the toes of giants.
http://www.ne.jp/asahi/julesandjames/home/

in message <[email hidden]>, James Annan

(') said:

until one (well, me at least) can only resort to increasingly
desperate and wild waving around of the arms. This can generate small
temporary torques,

Thank you, that is what I said.

Quoted message said:

but has little to do with normal bike riding (even
hands off)

Evidence, please? I believe it has everything to do with normal bike
riding. You are, of course, correct that balancing on a _moving_ bike
is substantially easier than balancing on the edge of a plank, but that
is because very small control inputs ('small temporary torques', in
your own words) are sufficient, in conjunction with the sensitive
lean-steering of a conventional bicycle, to keep the show on the road.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

Age equals angst multiplied by the speed of fright squared.
;; the Worlock

in message <[email hidden]>, James Annan

(') said:

Simon Brooke said:

Certainly. The issue is entirely in the rapidity of acceleration and
deceleration of body movement, exploiting inertia. If it were not
possible to adjust balance in this way, riding a unicycle, for
instance, or walking on a tightrope, would be impossible. Yet they
are not. If it can be done on a tightrope, why is it impossible on a
bicycle?

As I've already mentioned, the tightrope moves laterally under the
performer.

I suggested to you that you try this yourself with a line on the floor.
Are you suggesting that the whole building moves? If the whole building
does not move, how does the trick work?

Quoted message said:

Now, back to the cyclist. Assume this time he is not a circus
performer. How does he apply sufficient torque to himself to move
himself bodily from one side to the other of the contact patch. If you
believe he can do this, do you also believe he can ride a bicycle with
the forks locked straight ahead? If not, why not? Surely the same
"adjust your balance annd carry on normally" trick should work there
too, shouldn't it?

No, clearly you can't, because that bike cannot turn; a normal bike
turns if you lean it. It is this fact combined with body movement which
makes riding no hands possible - I assume you _can_ ride no hands.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

Morning had broken. I found a rather battered tube of Araldite
resin in the bottom of the toolbag.

Simon Brooke said:

in message <[email hidden]>, James Annan
([email hidden]'😉 wrote:

Quoted message said:

I suggest you try riding a bicycle. You will find that if you lean

the

Quoted message said:

bicycle to one side, it will turn to that side, without any need for
any other steering input. If you lean your body to one side, thus
moving your centre of gravity, then the bike will naturally lean to

the

Quoted message said:

other side, and thus you can easily initiate a turn in either
direction. You can demonstrate this easily by holding the bike by the
back of the saddle and pushing it along at walking pace; the bike is
easy to control just by leaning it. Or just ride no hands.

You should read David Jones paper on the Unrideable Bicycle (_The
Stability of the Bicycle_, Physics Today 23, 34-36); you would find

it

Quoted message said:

instructive. There's a PDF on the net somewhere but I've lost the

link.

The paper is concerned with the stability of the bicycle, and at least
lays the gyroscopic theory to rest, but does not appear to address the
issue of how a controlled turn is initiated. I don't think
counter-steering is even mentioned.

Certainly counter-steering can be used to initiate a turn. Try the
experiment of riding no-hands and giving one side or other of the bars
a gentle push forwards. The bike will lean to the pushed side and the
bars will turn against the push, entering a smooth turn. I am not
convinced, however, that this is the mechanism by which I normally
enter a turn. I feel as though the turn happens by itself and I just
control its magnitude.

Here's an alternative idea which may explain Jones' finding that a very
stable bike is difficult to ride, and why racers prefer bikes that are
less stable, or "twitchier", than utility riders would enjoy. As we
ride along we are all the time making minute corrections as the bike
begins to fall one way or the other. We must be doing this or riding
no-hands would be just as easy as hands-on. These corrections are in
the intuitive direction - the bars are turned towards the direction of
lean - and small and quick enough to take place at a subliminal level,
much like the corrections we constantly make in order to stand upright,
for example.

Now, when we wish to turn in one direction we simply stop correcting
when the bicycle naturally starts to fall that way, or over-correct
when it starts to fall the wrong way. When the turn has become as steep
as we wish we correct to stop it increasing further. To exit the turn
we correct some more. Everything is intuitive and we are not aware of
any action on our part to initiate the turn. Learning to ride a bike is
a process of training the nervous system to associate the appropriate
movements with correcting the imbalance. Very like walking, the time
this process takes varies from one individual to another, but once
complete is permanent. It's a truism that you never forget how to ride
a bike.

This also explains why it is so difficult to make a sudden turn. You
cannot turn by the normal process any sooner or any more rapidly than
the bike would naturally have fallen anyway. You can, however, rapidly
initiate a steep turn by counter-steering. This can be learned and
performed consciously but is not intuitive.
That's my theory at any rate.

--
Dave...

Simon Brooke said:

a normal bike
turns if you lean it. It is this fact combined with body movement which
makes riding no hands possible - I assume you _can_ ride no hands.

It depends on the geometry - I can ride no hands on my town runaround,
but on my elderly road bike it's impossible. [1]

R.

[1] FCVO "impossible".

Simon Brooke said:

in message <[email hidden]>, James Annan
([email hidden]'😉 wrote:

Quoted message said:

Quoted message said:

Now, back to the cyclist. Assume this time he is not a circus
performer. How does he apply sufficient torque to himself to move
himself bodily from one side to the other of the contact patch. If

you

Quoted message said:

Quoted message said:

believe he can do this, do you also believe he can ride a bicycle

with

Quoted message said:

Quoted message said:

the forks locked straight ahead? If not, why not? Surely the same
"adjust your balance annd carry on normally" trick should work
there too, shouldn't it?

No, clearly you can't, because that bike cannot turn; a normal bike
turns if you lean it. It is this fact combined with body movement
which makes riding no hands possible - I assume you _can_ ride no
hands.

The bike would not need to turn. In order to ride a straight line the
cyclist would simply need to keep the combined CofG of himself and the
bike directly over the line between the contact patches of the two
tyres.

--
Dave...

in message <[email hidden]>,

dkahn400 (') said:

Simon Brooke said:

in message <[email hidden]>, James Annan
([email hidden]'😉 wrote:

Quoted message said:

Quoted message said:

Now, back to the cyclist. Assume this time he is not a circus
performer. How does he apply sufficient torque to himself to move
himself bodily from one side to the other of the contact patch. If

you

Quoted message said:

Quoted message said:

believe he can do this, do you also believe he can ride a bicycle

with

Quoted message said:

Quoted message said:

the forks locked straight ahead? If not, why not? Surely the same
"adjust your balance annd carry on normally" trick should work
there too, shouldn't it?

No, clearly you can't, because that bike cannot turn; a normal bike
turns if you lean it. It is this fact combined with body movement
which makes riding no hands possible - I assume you _can_ ride no
hands.

The bike would not need to turn. In order to ride a straight line the
cyclist would simply need to keep the combined CofG of himself and the
bike directly over the line between the contact patches of the two
tyres.

I suspect that's not possible (or at least exceedingly difficult) unless
you are a highly trained acrobat. In any case, places where you could
ride a bike which is only capable of travelling in a straight line are
pretty rare.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
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M- !d- PS++ PE-- Y+ PGP !t 5? X+ !R b++ !DI D G- e++ h*(-) r++ y+++
------END GEEK CODE BLOCK------

in message <[email hidden]>, Richard

(') said:

Simon Brooke said:

a normal bike
turns if you lean it. It is this fact combined with body movement
which makes riding no hands possible - I assume you _can_ ride no
hands.

It depends on the geometry - I can ride no hands on my town runaround,
but on my elderly road bike it's impossible. [1]

Oh, indeed. When I first got my Jekyll I couldn't ride it no hands. I
thought this must be a feature of the lefty fork until I took the
remote rear lockout control off, when it became easy to ride no
hands... it was the springyness of the cable which had been upsetting
the handling.

Bike steering is by and large pretty sensitive; it needs only very small
forces to steer a bike.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; If you're doing this for fun, do what seems fun. If you're
;; doing it for money, stop now.
;; Rainer Deyke