Ratiotrol DC motors have specific characteristics to match the controls with which they operate. Thus, it is not necessary that a motor and control be mated; any stock motor will operate with a stock control of suitable rating within a series.
Standard motors have a base speed of 1750 RPM and are stocked in ratings from 1/6 through 5 HP. Operating characteristics, reliability and durability are similar; PM motors do offer advantages such as smaller size, lower weight and the absence of field hum on critical applications. In addition, installation is simplified since only two armatures leads need be connected.