If the field is constant then there is no change in time, and so d?/dt = emf = zero
I still don't understand you...what about this principle:
"A charged particle moving in a B-field will feel a sideways force that is proportional to the strength of the magnetic field, the component of the velocity that is perpendicular to the magnetic field and the charge of the particle. This force is known as the Lorentz force"
BTW, I created this image with Vizimag, which shows fairly accurately the field between two magnets as they are in the generators.