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
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