savonius rotor

[boobesque]

ok. i have built a small scale savonius rotor. the big one will be coming soon. lets assume that each wedge will be 4ft wide and 2 wedges will be connected at halfway points making the total diameter 6 ft wide. to get the most rpm out of this would i be better joining the wedges further apart ie at 3/4 the width and/or would wider wedges, after taking into consideration the added weight and drag, be at all beneficial? i probably havent explained this very well. sorry. thanks in advance for any replies

[gen2]

As a result of this question I have just spent an enjoyable hour broadening my knowledge of wind generators. Most designs I found on the web have an overlap of 50%.

It would appear you have three choices:
Zero overlap
Weld each section to a central shaft for greater strength and rigidity, but lower efficiency.
50% overlap
Greater efficiency but weaker structure.
Modified shape
Flattening the inside curves of each wedge involves more constructional work but leads to even greater efficiency.

Also, I am not sure of the relative merits of a two-tier design offset by 90 degrees, or a three tier design where each is offset by 60 degrees.

[boobesque]

the modified shape idea is a fab idea. i will probably try this. not sure why i didnt think of it to be honest. i think that the 3 tier designs benefits would be negligable over the 2 tier as the wind direction changes frequently enough anyway. thanks for the response

[BillyBB]

Great stuff, please post some photos when you have finished. Are you connecting to an alternator? If so are you gearing up or connecting direct? And what are you hoping to run with the electricity?

[boobesque]

probably direct to an alternator. i am however considering gears to create extra rpm but i havent yet decided whether i can be bothered. not sure what i intend to power. it is a labour of interest more than anything. i am going to try to fashion a ups system between the alternator and whatever device i may power as well. watch this forum for more questions which i no doubt will have.

[BillyBB]

Probably easiest to use pulleys, most alternators have one already.

[boobesque]

i was actually thinking of dismantling an old mountain bike and mount the mill on the pedal gears and the alternator on the back wheel. this will probably look a little odd on my roof. not many people where i live keep there bikes on the roof