>> target is very low wind speed, trivial power out
>
> I want to do something like this. =A0Some sort of convenient semi-
> tubular piece of trash mounted on a discarded CD drive spindle motor
> (or one at the top an one at the bottom?), perhaps with much of the CD
> drive mechanics still intact. =A0Put it on the roof and measure the
> output...

See my prior comments.
You'd need advanced Savonius blades to get 1 Watt/ m^2 at 2 m/s. This
increases with cube of wind speed.
ie 125 Watts / m^2 at 10 m/s.
I want something that makes 1 Watt if you can feel the breeze on your face.

Most promising motor so far is 1.44 MB floppy disk as it is low RPM
compared to CD motor.
Good iron and magnetics to play with
Most BLDCMs can be used by bypassing the drive IC. Rewinding for
higher voltage per rpm is often desirable

Main trouble with CD motor and Savonius is speed mismatch.
Savonius as per my recent posts is only TSR ~=3D 1 so low rpm wrt lift WTs.
That's why the idea of a long and low dia rotor is useful.
~- 200 RPM per m/s at 100 mm dia.

I have a $1 bucket on a metal pie plate on an inline skate bearing as
a demonstrator of 'how low can you go" $ wise.
Extremely low wind speed start up (unloaded). Savonius has good torque
and good startup compared to most alternatives.

Benesh profile blades do not allow use of buckets and barreles (unless
you beat them severely) but is easy and cheap with sheet material and
signifi=3Dcantly superior to bucket style.

Beware the Rahai profile. His results look good for single blades but
are probably inferior to Benesh when in a real machine.

If you use a large diameter alternator with many poles you get better
low speed performance for give magnetics and windings.

Someone asked about gearing etc multiple rotors together. It's doable
but for low powers and with lowish quality designs (non rigid
structures,  plastic gears etc) the power losses can easily exceed the
modest power available. I'm going to try "magnetic drive" coupling.
May not be economic. One advantage of gearboxes is the ability to
increase alternator speed. but unless some form of clutch or careful
magic is used the reflected load often makes startup torques
unacceptable. Even cogging (saliency) in direct drive alternators is
often the limiting factor in startup wind  speed.


               Russell

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