Science of Bikes (the physics behind ghost riding a bike)

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dwillen
Participant
#

Science Friday video, for lay audiences:

http://www.sciencefriday.com/videos/watch/10376

Science paper, for the geeks:

J. D. G. Kooijman, J. P. Meijaard, Jim M. Papadopoulos, Andy Ruina, and A. L. Schwab, Science, Vol. 332 no. 6027 pp. 339-342, April 15, 2011, doi:10.1126/science.1201959

and a podcast from Science:

http://www.sciencemag.org/content/332/6027/339/suppl/DC2

a website from the authors:

http://bicycle.tudelft.nl/stablebicycle/

The abstract:

A riderless bicycle can automatically steer itself so as to recover from falls. The common view is that this self-steering is caused by gyroscopic precession of the front wheel, or by the wheel contact trailing like a caster behind the steer axis. We show that neither effect is necessary for self-stability. Using linearized stability calculations as a guide, we built a bicycle with extra counter-rotating wheels (canceling the wheel spin angular momentum) and with its front-wheel ground-contact forward of the steer axis (making the trailing distance negative). When laterally disturbed from rolling straight, this bicycle automatically recovers to upright travel. Our results show that various design variables, like the front mass location and the steer axis tilt, contribute to stability in complex interacting ways.


AtLeastMyKidsLoveMe
Participant
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Hey, that looks really interesting, but can you post it in English, too?


robjdlc
Participant
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Thats what the video is for. :p

This is why the trick to riding without hands is to not correct the bike too much. Neat stuff.


edmonds59
Participant
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I haven’t read the paper yet, that’s going to take some time. But, just intuitively, it seems like a second set of counter rotating wheels would not cancel gyroscopic resistance to turning, but would double it, since force put into a gyroscope is redirected at 90 deg, the second set would resist turning at the opposite 90 deg, making it nearly impossible to turn whatsoever. Maybe.


dwillen
Participant
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Nope, two identical discs spinning in opposite directions on the same axis have no angular momentum, and will act as if they’re not spinning at all.


quizbot
Participant
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Erica
Participant
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That is fantastic.


edmonds59
Participant
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I finally watched the video, really excellent. It almost makes me wish I could do math.

The close-ups of the Bianchi track bike gave me warm feelings.

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