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On Tue, 5 Aug 2003 14:32:51 +0100, "Dave Larrington" <[email protected]> wrote:

>http://news.bbc.co.uk/1/hi/magazine/3125341.stm
>
>Oh
>
>My
>
>God

Hi Dave

Maybe it's a subliminal something or other - I read your post before I clicked on the URL - but the
very first words I said when I saw Sir Clive on the Segway were 'Oh my God' - complete with spaces.

The BBC site states: "... the Segway uses gyroscopes to stay upright." Don't bicycles stay upright
because of the gyroscopic action on their wheels. (Yes, I know that's extremly badly put.) Calling
all physicists.

James

--
http://homepage.ntlworld.com/c.butty/Larrau.jpg
 
"James Hodson" <[email protected]> wrote in message

> Don't bicycles stay upright because of the gyroscopic action on their wheels. (Yes, I know that's
> extremly badly put.) Calling all physicists.

Nope, not gyroscopes, more like hockey sticks or golf clubs - balancing one of these on the palm of
your hand is the same problem as balancing a bike.

's an FAQ too...

cheers, clive
 
In message <[email protected]>, James Hodson
<[email protected]> writes
>On Tue, 5 Aug 2003 19:30:28 +0100, "Clive George"

>>"James Hodson" <[email protected]> wrote in message

>>> Don't bicycles stay upright because of the gyroscopic action on their wheels. (Yes, I know
>>> that's extremly badly put.) Calling all physicists.

>>Nope, not gyroscopes, more like hockey sticks or golf clubs - balancing one of these on the palm
>>of your hand is the same problem as balancing a bike.

>OK, Clive. Next question: Why is balancing easier on a moving bike than on a stationary,
>track-standing one?

You balance a moving bike by steering it - first you go over a bit one way, then over a bit the
other way, etc. You can't do that when stationary.

--
- Jack Howard, Systems Development Engineer, Firstnet Services Limited
===[ http://www.firstnet.net.uk <--- Total Internet Solutions ]===

===[ This message subject to http://www.firstnet.net.uk/disclaimer.html ]===
 
On Tue, 5 Aug 2003 19:30:28 +0100, "Clive George"

>"James Hodson" <[email protected]> wrote in message
>
>> Don't bicycles stay upright because of the gyroscopic action on their wheels. (Yes, I know that's
>> extremly badly put.) Calling all physicists.
>
>Nope, not gyroscopes, more like hockey sticks or golf clubs - balancing one of these on the palm of
>your hand is the same problem as balancing a bike.
>

OK, Clive. Next question: Why is balancing easier on a moving bike than on a stationary,
track-standing one?

James

--
http://homepage.ntlworld.com/c.butty/Larrau.jpg
 
"James Hodson" <[email protected]> wrote in message
news:[email protected]...
> On Tue, 5 Aug 2003 19:30:28 +0100, "Clive George"

>
> >"James Hodson" <[email protected]> wrote in message
> >
> >> Don't bicycles stay upright because of the gyroscopic action on their wheels. (Yes, I know
> >> that's extremly badly put.) Calling all physicists.
> >
> >Nope, not gyroscopes, more like hockey sticks or golf clubs - balancing
one
> >of these on the palm of your hand is the same problem as balancing a
bike.
> >
>
> OK, Clive. Next question: Why is balancing easier on a moving bike than on a stationary,
> track-standing one?

How do you hold the hockey stick up? By moving your hand around underneath it to catch the fall. If
you're stationary on a bike you can't do this. If you're moving you steer so the bottom of the bike
moves underneath you to catch the fall.

cheers, clive
 
"James Hodson" <[email protected]> wrote in message
news:[email protected]...
> The BBC site states: "... the Segway uses gyroscopes to stay upright." Don't bicycles stay upright
> because of the gyroscopic action on their wheels. (Yes, I know that's extremly badly put.) Calling
> all physicists.

I'm not a physicist. But I do know that the stability of bicycles is nothing (well, almost nothing)
to do with gyroscopic action, unless you have extremely massive or fast spinning wheels - neither of
which are common on bicycles. It's all to do with the geometry of the front forks. A chap called
David E.H. Jones published a paper about it in 1970, which can be found in PDF format here:
http://ist-socrates.berkeley.edu/~fajans/Teaching/MoreBikeFiles/JonesBikeBW.pdf It tells you
everything you probably need to know about the subject.

Andrew.
 
On Tue, 5 Aug 2003 19:51:50 +0100, "Clive George"

>How do you hold the hockey stick up? By moving your hand around underneath it to catch the fall. If
>you're stationary on a bike you can't do this. If you're moving you steer so the bottom of the bike
>moves underneath you to catch the fall.
>

OK guys. I have the idea now. Thanks.

James

--
http://homepage.ntlworld.com/c.butty/Larrau.jpg
 
In news:[email protected], James Hodson
<[email protected]> typed:
>
> The BBC site states: "... the Segway uses gyroscopes to stay upright." Don't bicycles stay upright
> because of the gyroscopic action on their wheels. (Yes, I know that's extremly badly put.) Calling
> all physicists.

that entered poular mythology many years ago but was disproved by a simple experiment of setting up
a slightly smaller wheel which counter rotated at the same speed as the bike wheel ie giving equal
and oposite angular momentum along the wheel axis. Balance and steering were unchanged.

a less rigourous dis-proof is to consider slow speed balance when any gyro scopic effect is minimal.

Sterring and balance have more to do with bike geometry esp the "trail" (horizontal distance between
stering axis and point of contact of the front wheel with the ground.

p - ex physicist - k
 
On Tue, 05 Aug, James Hodson <[email protected]> wrote:
> On Tue, 5 Aug 2003 19:30:28 +0100, "Clive George"

> >"James Hodson" <[email protected]> wrote in message
> >
> >> Don't bicycles stay upright because of the gyroscopic action on their wheels. (Yes, I know
> >> that's extremly badly put.) Calling all physicists.
> >
> >Nope, not gyroscopes, more like hockey sticks or golf clubs - balancing one of these on the palm
> >of your hand is the same problem as balancing a bike.
>
> OK, Clive. Next question: Why is balancing easier on a moving bike than on a stationary,
> track-standing one?

'cos the mechanism by which the bike is moved sideways depends on teh fact that teh wheel is
rolling forward.

When balancing said hockey-stick, you move your hand side to side. Track-standing is more like
balancing teh hockey stick without moving your hand. Altogether trickier.

regards, Ian SMith
--
|\ /| no .sig
|o o|
|/ \|
 
Clive George must be edykated coz e writed:

> "James Hodson" <[email protected]> wrote in message
> news:[email protected]...
>> On Tue, 5 Aug 2003 19:30:28 +0100, "Clive George"

>>
>>> "James Hodson" <[email protected]> wrote in message
>>>
>>>> Don't bicycles stay upright because of the gyroscopic action on their wheels. (Yes, I know
>>>> that's extremly badly put.) Calling all physicists.
>>>
>>> Nope, not gyroscopes, more like hockey sticks or golf clubs - balancing
> one
>>> of these on the palm of your hand is the same problem as balancing a
> bike.
>>>
>>
>> OK, Clive. Next question: Why is balancing easier on a moving bike than on a stationary,
>> track-standing one?
>
> How do you hold the hockey stick up? By moving your hand around underneath it to catch the fall.
> If you're stationary on a bike you can't do this. If you're moving you steer so the bottom of the
> bike moves underneath you to catch the fall.
>
> cheers, clive
>
Gyroscopic effect does come into play, more so as you move faster, the specific mass of the wheels
increase due to velocity, and the centripedal force generated within the wheels mass area becomes
more difficult to deflect off line, but at slower speeds the bicycle is balanced by the rider
shifting weight about, usually without thinking about it, both by moving the body and by altering
the steering, so all answers are correct.

Ian
 
On Tue, 5 Aug 2003 19:28:49 +0000 (UTC), "Paul Kelly" <[email protected]> wrote:

>Sterring and balance have more to do with bike geometry esp the "trail" (horizontal distance
>between stering axis and point of contact of the front wheel with the ground.

My 8 year old has one of those micro scooters. The "fork" is a simple folded bracket and is near
(but not quite) symmetrical. The bars/fork can rotate in a complete 360°.

His mum (we're divorced and live quite a distance apart) isn't a cyclist and doesn't appreciate
such things. So neither of them had ever noticed that with the bars one way round the thing is
completely unstable (I can barely stay on at walking pace), yet spin the bars through 180° and it's
easy to ride. The trail in this fork can't be more than 1/2", yet it's enough to totally transform
the handling.

Some marker pen work on labelling the bars made future riding a bit more predictable.
 
Andy Dingley wrote:
> On Tue, 5 Aug 2003 19:28:49 +0000 (UTC), "Paul Kelly" <[email protected]> wrote:
>
>> Sterring and balance have more to do with bike geometry esp the "trail" (horizontal distance
>> between stering axis and point of contact of the front wheel with the ground.
>
> My 8 year old has one of those micro scooters. The "fork" is a simple folded bracket and is near
> (but not quite) symmetrical. The bars/fork can rotate in a complete 360°.
>
> His mum (we're divorced and live quite a distance apart) isn't a cyclist and doesn't appreciate
> such things. So neither of them had ever noticed that with the bars one way round the thing is
> completely unstable (I can barely stay on at walking pace), yet spin the bars through 180° and
> it's easy to ride. The trail in this fork can't be more than 1/2", yet it's enough to totally
> transform the handling.
>

Well bugger me! I've just been up and down the street on my daughters's micro scooter and you are
quite right. One way round easy t'other unstable steering!

I've never noticed before as there is an abvious right and wrong way round from the paintwork and
labelling!

pk
 
"James Hodson" <[email protected]> wrote in message
news:[email protected]...
> On Tue, 5 Aug 2003 14:32:51 +0100, "Dave Larrington" <[email protected]> wrote:
>
> >http://news.bbc.co.uk/1/hi/magazine/3125341.stm
> >
> >Oh
> >
> >My
> >
> >God
>
> Hi Dave
>
> Maybe it's a subliminal something or other - I read your post before I clicked on the URL -
> but the very first words I said when I saw Sir Clive on the Segway were 'Oh my God' - complete
> with spaces.
>
> The BBC site states: "... the Segway uses gyroscopes to stay upright." Don't bicycles stay upright
> because of the gyroscopic action on their wheels. (Yes, I know that's extremly badly put.) Calling
> all physicists.
>
> James
>
> --
> http://homepage.ntlworld.com/c.butty/Larrau.jpg

Hold the front page the lot of you....everyone knows it's down to the stabilisers!!! ;-) Dave.
 
I believe you balance a bike in three ways. The relative importance of each strategy depends on how fast the bike is moving.

1. If the bike is stationary the only thing you can possibly do is to shift bits of your body (and/or bike) around to keep your centre of mass over the line between the contact points of the wheels.

2. When the bike is moving you can re-establish equilibrium by steering in the direction of fall. At low speeds this simply works by moving the support line back beneath your centre of mass. It's easy to see this happening when you stand on the pedals to climb a hill: the wheels track from side to side to compensate for shifts of the upper body.

3. Centrifugal force caused by the turn provides a balancing force to gravity. The gravitational force, acting in a vertical plane, and the centrifugal force, acting in a horizontal plane, resolve into a force acting through the support line. This is why you bank the bike when you take a corner. As long as your tyres don't slide sideways the result is stable.

I don't think gyroscopic effects are significant. Bikes (or scooters) with tiny or very light wheels aren't noticeably harder to balance than those with big heavy wheels. I've read that the forces resulting from gyroscopic action of a spinning bike wheel are trivial compared to the mass of the bike and rider. And it's not clear how the gyroscopic forces are supposed to keep the bike balanced. Imagine yourself trying to stand on a board on top of a bowling ball - do you think it would be any easier if you had a couple of spinning wheels to hold?

The shape of the forks, or rather the position of the front wheel with respect to the axis of the headset, probably makes steering harder or easier, and this is why it affects balance.

(Apologies to any physicists for the mangled concepts above, but I think the ideas are fundamentally correct. It seems to work for me, as I haven't fallen off for a while.)

Chris (definitely not a physicist) Walker

Originally posted by Jack Howard
In message <[email protected]>, James Hodson
<[email protected]> writes
>On Tue, 5 Aug 2003 19:30:28 +0100, "Clive George"

>>"James Hodson" <[email protected]> wrote in message

>>> Don't bicycles stay upright because of the gyroscopic action on their wheels. (Yes, I know
>>> that's extremly badly put.) Calling all physicists.

>>Nope, not gyroscopes, more like hockey sticks or golf clubs - balancing one of these on the palm
>>of your hand is the same problem as balancing a bike.

>OK, Clive. Next question: Why is balancing easier on a moving bike than on a stationary,
>track-standing one?

You balance a moving bike by steering it - first you go over a bit one way, then over a bit the
other way, etc. You can't do that when stationary.

--
- Jack Howard, Systems Development Engineer, Firstnet Services Limited
===[ http://www.firstnet.net.uk <--- Total Internet Solutions ]===

===[ This message subject to http://www.firstnet.net.uk/disclaimer.html ]===
Click to expand...
 
In message <[email protected]>, James Hodson
<[email protected]> writes

<snip>

>The BBC site states: "... the Segway uses gyroscopes to stay upright."

Just in case there's any confusion, the gyroscopes on the Segway aren't big spinning masses, but are
small micromachined chips. They're not gyroscopes in the conventional sense, but rather sensors
which measure the rate of angular rotation. The signal outputs from these are used by a program
running in a microcontroller, along with other information, to drive the Segway motors so as to keep
the platform nominally level.

Personally, I think that a less expensive Segway with limited top speed
- say 5MPH - could be a boon to the arthritic elderly. There are many people who live for years
being able to stand and walk a little, but can't manage the half-mile to the local shop.

Cheers
--
Keith Wootten
 
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