Electric generator build v0.1

Its me building a simple electric generator. I'm not entirely sure my maths in right. Please correct me if you think its wrong and any advice is welcome.
I might do a second part with more RPM / magnets and maybe i will have enough juice for an LED.
Parts
www.amazon.co....
www.amazon.co....
Here is the calculation for magnetic density.
Br = 1.22
L = 0.05
W = 0.01
D = 0.003
z = 0.003
B = (Br/pi) * (atan((L*W)/(2*z*sqrt(4*z^2+L^2+W^2))) ...
atan((L*W)/(2*(D+z)*sqrt(4*(D+z)^2+L^2+W^2))))