On Fri, 14 Sep 2007 12:21:17 +1000, Jordan wrote:

I've volunteered to help an artist, who wants to place a number of small
vertical rotor windmills in a seaside park, on top of picnic sheds. (He
has permission!)

The rotors will be about 6 ft diameter, 3 ft high, and free-spinning -
won't drive anything.
The challenge is how to control the things so they don't spin too fast,
but still be able to start in a light breeze.

Of course, cost matters.

Ideas so far:
1. Centrifugal-operated "air brake".
2. Permanent-magnet motor, with speed-sensing switch to short out for
back-emf braking.
3. Sails attached with Velcro, to rip out in big wind.


Centrifugal clutch, a la:

http://www.gokartsupply.com/clutches.htm

You put the shaft on the centrifugal part, and tie down the clutch
part. :-)

Good Luck!
Rich