A pancake type direct current motor is disclosed which comprises a motor drive shaft with one or more rotor assemblies secured along the motor drive shaft. An even number of spaced stator poles surrounds each of the one or more rotor assemblies. Each stator pole has an associated excitation...http://www.google.com.hk/patents/US6169349?utm_source=gb-gplus-share專利 US6169349 - Electromagnet type segmented field DC motor
