"Jordan" wrote in message
u...
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.

All comments and suggestions welcome.

Jordan

Take a look at the centrifugal speed controllers on the old steam engines.
The perfect solution in that they are simple, dependable, cost effective,
and will not hinder low breeze operations.... Two balls rotating and the
faster they go the tighter the pull on the brake lining. You can see the
same effect on small motor drives like in a scooter. Rev up the motor and
the clutch engages to drive the pup.