Turning without countersteering: photographs and test results

Ian Smith

On 17 Dec 2004 08:25:53 -0800, dkahn400 <dkahn400@yahoo.co.uk> wrote:
>
> Think carefully about this. We're considering someone sticking their
> left arm out, first standing then rolling along in a straight line on a
> bike. I claimed that as the arm moves to the left there must be an
> equal reaction to the right, according to Newton's third law.

How about reacting against teh inertia of teh rest of teh body? If
your argument was infallible, cats would not be able to land on their
feet...

regards, Ian SMith
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Richard

dkahn400 wrote:
>
> Now imagine you are seated on your bicycle. I am standing beside you
> and you are leaning very slightly against me, almost upright. The
> slightest push from me will topple you. You are in intimate contact
> with the bike and its contact area with the ground. Short of putting a
> foot down or grabbing hold of me there is nothing you can do to resist
> that push.

Yes, there is; if the push is momentary and of sufficiently small
magnitude that the pusher can react before they hit the ground, *and the
pusher moves out the way fast enough* the pushee can jerk his/herself
back upright, in exactly the same way that a person standing on one foot
can do so. The danger with this sort of experiment when carried out
for real rather than in the gedankenrealm is that the pusher remains
with their pushy bit extended rigid (ooh, er, missus) for sufficient
time that the pushee can't push themselves back up because the pushy bit
is still in the way.

Of course, what usually happens balancing on a stationary bike is that
the pushee overcompensates the initial push, tries to compensate for
that, etc, and eventually (FCVO 'eventually') goes too far one way or
the other to recover. A similar phenomenon is known to pilots as PIO,
pilot-induced oscillation; a plane in level flight encounters a small
disturbance which brings the nose up or down in pitch, say down. The
pilot overcompensates too far, the nose rises, he pushes down but
overcompensates too far again, the nose dives even more, and the
resultant oscillations grow in magnitude.

R.

Tim Woodall

On Fri, 17 Dec 2004 11:42:34 -0000,
Clive George <clive@xxxx-x.fsnet.co.uk> wrote:
> "David Martin" <d.m.a.martin@dundee.ac.uk> wrote in message
> news:BDE8722F.5F2F%d.m.a.martin@dundee.ac.uk...
>
>> What about a swing? Surely it is impossible for a swing to start moving
> from
>> rest if there is always a net resultant of 0.
>
> In the absence of friction is this the case? Would a swing work on the moon?
>
<strictly theoretical>
Actually yes, even if the only action that you can make is to stand up
and sit down.
It is actually impossible to have a completely stationary simple
harmonic oscillator (this is second year undergraduate physics) and
standing and sitting (at the right times) can pump the oscillator.

(OK, so a swing isn't strictly an SHO which means that you can't solve
the physics for it exactly[1] but it still applies)

[1] There are three problems that can be solved in physics, the SHO, the
infinitely deep square potential well and the two body problem.
Everything else is an approximation.

Tim.

--
God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H = J + @D/@t,"
and there was light.

http://tjw.hn.org/ http://www.locofungus.btinternet.co.uk/

Tim Woodall

On 17 Dec 2004 14:17:58 GMT,
Mark Thompson <pleasegivegenerously@warmmail.com> wrote:
><simpleton>
>
> So on the bike, by leaning to the left we can make the bike go left
> without having to move the steering. Presumably it's only a small lean
> but once it's started gravity helps with the rest?

I wasn't going to get involved but oh well :-)

Assuming everything is theoretically perfect - vacuum, tyre that has a
round cross section with no deforming, frictionless headset, perfectly
flat road etc, etc, etc.

When you lean to the left the bike leans to the right (you can ride the
bike like this quite easily and some people actually suggest it for
riding in the wet - some also suggest the opposite of leaning the body
and not the bike and yet others say just lean everything - I'm making no
judgement although I try to keep everything straight but nervousness
tends to mean I err a bit to the upright bike leaning body even though
intellectually I suspect that keeping everything straight is safer)

At this point the CoG stays in the same place above the tyre.

Because the bike leans to the right the steering turns to the right but
you keep leaning left.
This causes the bike to move right so the tyres move out from under the
CoG. Also the right turn causes a "centrifugal" force which causes the
bike to lean to the left.

The bike leans to the left and the steering turns to the left and you
now go around the corner because you maintain the left lean.

When you want to stop turning you "lean to the right" i.e. back upright.
This causes the bike to lean more to the left
This causes the steering to turn more to the left
This causes the CoG to move to the right
This causes a force that brings the bike back upright underneath you.



Note that you are countersteering, even though you don't know it. You
really are leaning to the left to turn left but, initially, your left
lean actually causes a _automatically_self_correcting_ turn to the right
of the bike.


HTH


Tim.

>
> Thinking about falling off my bike again, I could probably make a non
> steerable bike fall whatever way I wanted to. To eliminate any
> possibility of countersteering being involved I could do it stationary
> too.
>
> If I can make a bike lean the way I want it to turn without
> countersteering does it not follow that I could turn without
> countersteering.
>
> This thread's stupidly long so I presume it isn't this simple. When
> someone disagrees with my post could you just explain what on earth you
> mean by 'countersteering' first.
>
> thx.
>
>
> ps I thought countersteering was briefly turning right to go left. My
> simple method of turning without countersteering is leaning left while
> steering left.
>
></simpleton>


--
God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H = J + @D/@t,"
and there was light.

http://tjw.hn.org/ http://www.locofungus.btinternet.co.uk/

James Annan

David Martin wrote:


>
> So, your evidence for only a tiny proportion of people being able to do
> something most have never tried is..?

For starters, we've all tried, cos when the speed drops, so does the
steering response (in terms off the lateral motion off contact patch in
responce to handlebar turning)

For a follow-up, why don't you just go and read that David Jones article
that was cited earlier.

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

Mark Thompson wrote:

>>>What about a swing? Surely it is impossible for a swing to start
>>>moving from rest if there is always a net resultant of 0.
>>
>><snippity> It is actually possible <snippity>
>
>
> <simpleton>
>
> So on the bike, by leaning to the left we can make the bike go left
> without having to move the steering. Presumably it's only a small lean
> but once it's started gravity helps with the rest?

It is possible in theory, for some value of "leaning to the left" (which
I think actually would mean leaning to the right, or more typically by
waving your arms about in the manner of someone trying to balance on a
very narrow plank edge).


> Thinking about falling off my bike again, I could probably make a non
> steerable bike fall whatever way I wanted to. To eliminate any
> possibility of countersteering being involved I could do it stationary
> too.
>
> If I can make a bike lean the way I want it to turn without
> countersteering does it not follow that I could turn without
> countersteering.

In theory, yes. If you could actually perform this control in practice,
you would be able to balance a non-steering bike by tipping your self
back up whenever you accidentally wobbled to one side (for a initially
small wobble, the effect of gravity pulling you over is very small).
Given that you are never going to be _perfectly_ balanced and steady
over the CoG in normal riding (it moves from side to side under you),
any claim of _control_ and _deliberate_ turning must include the case of
turning to the "uphill" side rather than merely falling off on the side
that you happen to already be on when you stop steering normally.

Otherwise, all you are claiming is the ability to fall off a bike when
you stop steering it normally. I'm sorry to have to break it to you, but
that is not really very exciting news. I don't believe that Simon was
considering such a semantic dodge when he first outlined his ideas,
although he may by now be coming round to it as an escape route....

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

Paul - xxx wrote:

> light-hearted disagreement over something that we all agree happens most of
> the time.

Maybe, but Simon has supplied his usual range of arrogant, patronising
and snide comments [1] towards people who have tried patiently to
firstly understand what he is trying to claim, and then to explain why
he is wrong. Just like in our last disagreement (the maths thing) where
once his mistake had been explained, he didn't have the decency to even
concede the point, still less apologise for his behaviour and thank
those who took the trouble to help him, but just slunk away as he now
seems to be doing again. I suppose it must be conceded that it is an
impressive display of trolling.

James
[1] So have I, but I have been right rather than wrong. You can like me
or hate me or ignore me as you choose, but it does not affect the truth
of my statements.
--
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

Ian Smith wrote:


> How about reacting against teh inertia of teh rest of teh body? If
> your argument was infallible, cats would not be able to land on their
> feet...

Cats are rotating about their own CoG, so I'm not sure how this is
relevant. But anyway, they can turn round by extending and retracting
their front and rear pairs of legs independently (thus changing their
moments of inertia at either end) and rotating in the middle
appropriately. Sticking the legs out acts somewhat as an anchor, that
end rotates less far than the one where the legs are pulled in.

They are actually not all that reliable at landing on their feet, from
the limited resarch I once found.

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

David Martin

James Annan wrote:
> David Martin wrote:
>
>
>>
>> So, your evidence for only a tiny proportion of people being able to do
>> something most have never tried is..?
>
>
> For starters, we've all tried, cos when the speed drops, so does the
> steering response (in terms off the lateral motion off contact patch in
> responce to handlebar turning)

No you haven't. you have tried a bike with *poor* response, not *no*
response.

> For a follow-up, why don't you just go and read that David Jones article
> that was cited earlier.

Why not repost the citation?

I was just intrigued by your suggestion that most people would not have
the ability to ride a particular type of bike, when clearly the vast
majority of people have not ever tried such a beast.


...d

Mark McN

Response to James Annan:
> > You've changed direction. Has counter-steering happened?"
>
> No.
>
> Now all you need to be able to do is maintain your balance in this
> state indefinitely, and then choose which side you want to fall to, and
> you will have proved that bicycles can be controlled without
> countersteering. Can you do this, even in your thought experiment?


The discussion seems to have moved on a little since my last post ;-),
and I think the issue has become clearer to me.

If you agree that a turn without countersteering is possible when the
CofG is already on the side of the turn, the only issue is how the CofG
got there.

As you said in a previous post, the CofG is continually moving around,
caused by previous micro-corrections, and requiring more micro-
corrections in turn; it seems pretty clear that if a micro-correction is
not made, a turn in the direction of the CofG will result.

AIUI (and I may well be wrong) you're defining countersteering as the
micro-correction (or, of course, a deliberate larger move) which puts the
CofG on the side of the intended turn. Am I right so far?


--
Mark, UK.
We hope to hear him swear, we love to hear him squeak,
We like to see him biting fingers in his horny beak.

James Annan

Mark McN wrote:


> AIUI (and I may well be wrong) you're defining countersteering as the
> micro-correction (or, of course, a deliberate larger move) which puts the
> CofG on the side of the intended turn. Am I right so far?

Yes, I think that's a reasonable description. Even if you dispute that
Simon's photo was clear, the principle is as indicated by the lines I
drew on it, and I think it will be generally clearly visible if you ride
a narrow-tyred bike through a puddle on a dry road, and then turn
sharply. The front wheel will not only follow a larger radius bend
(through the rear "cutting the corner") but also start by moving
outwards to initiate the lean.

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

Just zis Guy, you know?

On Fri, 17 Dec 2004 21:46:36 +0900, James Annan
<still_the_same_me@hotmail.com> wrote in message
<32g2mlF3jd0l3U2@individual.net>:

>> I'm missing something, too, and it is this: in what way is calling it
>> "countersteering" anything other than pointless pedantry? To say that
>> a bicycle cannot be steered left without first placing the rider's CoG
>> to the left of the contact points is self-evidently true. This is a
>> long way from the description of "countersteer" as a deliberate and
>> conscious act to precipitate a violent turn, as described in some
>> books.

>Maybe so, but Simon is not just debating the semantics, he really seems
>to believe that he has a method for balancing a bicycle that is
>physically different from the standard method of steering the contact
>patch under the rider.

Maybe, maybe not. I haven't read each post in detail because as I say
it sounds like a particularly silly argument but my understanding of
his original point (before Usenet hyperbole and digging-in took over)
is that you can steer without countersteering simply by waiting for
the bike to fall the right way, which eventually it will, plus a bit
of blurred distinctions between definitions of countersteer as either
a conscious and deliberate act to provoke a rapid turn, or a slightly
exaggerated part of the normal weaving motion of riding a bike.

Guy
--
"then came ye chavves, theyre cartes girded wyth candels
blue, and theyre beastes wyth straynge horn-lyke thyngs
onn theyre arses that theyre fartes be herde from myles
around." Chaucer, the Sheppey Tales

Ian Smith

On Sat, 18 Dec, James Annan <still_the_same_me@hotmail.com> wrote:
>
> Ian Smith wrote:
>
> > How about reacting against teh inertia of teh rest of teh body? If
> > your argument was infallible, cats would not be able to land on their
> > feet...
>
> Cats are rotating about their own CoG, so I'm not sure how this is
> relevant.

Because it demonstrates that it is possible to rotate a body (in teh
general sense) without having something solid to react against.

regards, Ian SMith
--
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|o o|
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Buck

Non of this countersteering rubbish on a tadpole trike.
--
I would rather be out on my Catrike