This is a question about brushless DC motors. (I should have put that in the title) How do you compare the two for an single geared vehicle drive system to get the widest power band in the same package size? I've been looking over the max flux density of soft iron vs. neodymium permanent magnets. The field strength of high grade neodymium is quoted at a B_r of 14K Gauss, and B_R of soft iron at about 18K Gauss. But for the soft iron, the required copper reduces the effective pole crosssection. (Can B_r and B_R be directly compared?) Variable field winding strength can nearly double the operating speed range by decreasing the field stength at higher RPM, or so I've read. Where do I start?