Hi Greystoke. The idea was to just add weight to the lower plate until the plates separate. Hmmm - I suppose you could use a jack too, attached to a large spring (fish) scale, which is attached to the lower plate. However, I'm hoping to do something that some guy in the middle of rural Africa could easily duplicate, which is why I'm trying so hard to make it need minimal technology.
Drawing is done with a full 3D design package, so I could use it to produce precise drawings for others to copy once we agree on a method.
The magnets of this shape are usually polarised towards the large faces, not lengthwise. For wind generators you want the flux coming off the rotor plates at a right angle (normal to the plane of rotation). So in my drawing they would be attracting (both magnets the same way, either both North up, or both South up).
Converting to flux density... not sure. Perhaps once you have done the weight test, you could use magnetism formulas to work out the flux density required to to produce a force equal in magnitude to F=ma for the weight of the lower plate at separation?