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Wikipedia article on automatic quartz watch describes the watch mechanism as follows: a rotating pendulum is attached to a pinion and when the wearer moves his hand the pinion is rotated at up to 100 thousand revolutions per minute and that pinion rotates an electric generator.

AFAIK the fastest hard disk drives currently reach only 15K RPM and they have serious problems with heat dissipation - a fan is required for cooling the drive.

How can a miniature pinion inside a watch be rotated at such speed without the whole assembly being worn out by friction in no time?

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This is simply wrong. Maybe the writer confused point and comma (translation problem) But nevertheless 100.000 (in american meaning) is nonsense too. – Georg Jul 4 '11 at 16:20
Also, just to note, 100k RPM would sound like a whinning (1.6kHz), no matter how small & isolated rotating part is. – BarsMonster Jul 4 '11 at 22:03
Also note that almost surely the 100k RPM is a theoretical upperbound, and for the most part the pinion will go much slower than that. The rate of rotation will depend on how fast the wearer is moving. – Willie Wong Jul 5 '11 at 0:21
up vote 4 down vote accepted

Why is 100K RPM an issue? Dental drills works at around 10 kHz, with is about 600K RPM. :-)

If you look at the Seiko Patent for the design of the Kinetic, the drive-train steps up the rotation of the spinning weight by 100 fold for the generator. When I charge my watch I shake it at around 5 - 10 Hz, which means 0.5-1 kHz for the small pinion, which gives 30 - 60k RPM indeed. So I don't think the Wikipedia article is that far off the mark.

When things are really small and light and precision made, I think you don't have to worry as much about heat dissipation and wear. (A typical hard-drive disk is about a couple inches in diameter. The pinion can't be more than a 10th of an inch, if you allow two steps to up the rotation speed.)

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You are wrong about the dental drills, and so ist the rest of Your reasoing. – Georg Jul 4 '11 at 18:25
Dental drills spin can go up to 400k rpm see [Dental drill ] – Fortunato Jul 4 '11 at 19:30

The rotation of the counterweight in the watch moves at that speed for a fraction of a second. Say if you hit a tennis ball the wait will only go 2 or tree turns and the initial speed can very well be at that speed. When your arm changes direction the weight will most likely stop. Now I don't know if calling the counterweight a "pendulum" is correct because all the math on a pendulum are based on gravity and the counterweight depends on changes of direction and momentum.

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