Physics eei help

physicskids1

Hey guys im currently proposing an eei for my year 12 physics class my idea is to make a small motor and then connect an axel with 3 fan heads as well as one with 4 and 2 heads, the question is to see why wind turbines use 3 heads instead of 4 or 2. i just need help with the making of the heads not to hard and not much money spent and maybe a place to buy the motor in brisbane qld australia. And any information tot he study of wind turbines would help a lot thank you.