how can i build a small efficient windmill generator?

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Question by Jake M: how can i build a small efficient windmill generator?
I want to build a small windmill generator for my tree house that will produce enough power for a light bulb. i was wondering what would produce more power, a generator with alot of copper coils, or more magnets.and other advice would be very helpful
also i want to be able to make it mostley from scratch.

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