Direct-current motor design as influenced by the use of the inter-pole

The advent of the inter-pole is due to the demand for motors which operate under conditions so severe that perfect results can not be obtained with those of the standard design. The machine-tool builders quickly saw the advantages of the individual motor drive, largely on account of the possibility of obtaining speed variations, but the 33% increase in speed which the standard constant-speed motor would allow was not sufficient for their requirements. As it seemed evident that the motor builders could furnish motors of special design that would satisfy almost any demand they might make in the way of speed changes, the tool builders have adapted their machines to this form of drive, and call for motors that will operate at from 100% to 500% above minimum speed.