Page 148 - Electric Drives and Electromechanical Systems
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Chapter 5 Brushed direct-current motors 141
FIG. 5.4 The key features of (A) radial and (B) axial field d.c. brushed motors. For clarity in the axial field or
printed-circuit motor only two magnet pairs and winding are shown. In practice up to eight magnet pairs are
typically used, together with a similar increase in windings.
with the winding arrangement as shown. A family of brushed printed circuit motors are
shown in Fig. 5.5.
The main constraint on the length of the motor is the size of the magnets. The motor
design could use either low-power ferrite magnets (to give a short motor) or Alnico
magnets (to give a longer, more powerful, motor). The use of neodymium-iron-based
magnetic materials has allowed high-power motors to be designed with minimum
lengths. In addition, these materials are now stable up to 150 C and this, combined with