
Researchers explain why bicycles balance themselves - flyingyeti
http://www.news.cornell.edu/stories/April11/bicycle.html
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dmlorenzetti
This publicity release mis-advertises what is new here.

From the publicity release: _Now, a new analysis says the commonly accepted
explanations are at least partly wrong. The accepted view: Bicycles are stable
because of the gyroscopic effect of the spinning front wheel or because the
front wheel "trails" behind the steering axis, or both._

From a Wikipedia article
(<http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics>): _In 1970,
David E. H. Jones published an article in Physics Today showing that
gyroscopic effects are not necessary to balance a bicycle._

In fact, Jones' article addresses the steering axis question, as well.

What appears to be new here is the mathematical analysis. From Jones: _I have
not yet formalized all these contributions into a mathematical theory of the
bicycle..._

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wiredfool
I had Ruina as a dynamics prof many years back. Good teacher, Good class.

I still remember that he was interested in self walking robots at the time,
powered only by gravity and walking down a slight slope.

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kragen
How do those work? With the Jansen linkage?

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wiredfool
I remember a three legged version, with the inner leg out of phase with the
outer two. This is a more refined two legged version,
<http://www.youtube.com/watch?v=_2pAMe_5VeY> .

Power here is gravity, in the form of a slight slope on the surface it's
walking on. The walking form is all from dynamic motion, no electronic
control.

It looks simpler than a jansen linkage, much more like the physiology of our
legs. (and there's a funny story there, Prof Ruina had a limp when he taught
the class, because he had implanted studs in the bones of one of his legs so
that they could motion capture the bone motion when he walked. Not sure if the
limp affected that.)

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hoag
This is awesome: I have seriously been searching for an explanation on this
ever since I was a little kid and my dad bought me my first bike at about 3
years of age and immediately removed the training wheels.

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vlisivka
> They built a bicycle with two small wheels, each matched with a counter-
> rotating disk to eliminate the gyro effects

...to double gyro effects... or I missed something?

Two conter-rotating disks will compensate each other, BUT they must be
perfectly aligned, is not?

In their bicycle, upper disk produces about 2x of gyro effect comparing to
lower disk gyro effect, because it moves with about 2x larger amplitude
comparing to lower disk at same incline, thus we still have about 2x-1x=1x
gyro effect.

They should try their system on skates with two tiny blades instead of wheels.

PS.

Sorry for my English - I am Ukrainian.

PPS. System need to spent some energy to restore vertical alignment of
inclined body.

Thus they need to add small incline to bicycle and then find where motion
energy is spent by bicycle to restore vertical alignment. If bicycle will
unable to restore vertical alignment then it is not stable.

