DC Motors are generally used in lower voltage applications where portability is the primary goal. Most DC Motors have brushes to switch the magnetic alignment to cause rotation. DC Motors operate over a wide range of voltages. A 12V DC Motor will operate down below 6V or up to over 15 or more. What is lost at low voltage is speed & torque. At a lower voltage, both friction and load will drop motor speed. Thus a DC Motor rated 1200RPM at 12V at no load will drop to near ½ Speed at 6V and torque will be much lower. At a high voltage the speed & torque will be higher but the DC Motor upper voltage range is limited by rotational force & heat. The best way to lower a DC Motor speed is through the use of Pulse Width Modulation (PWM) where full voltage is applied (therefore full torque available) but only for a adjustable period of time. The load will cause the DC Motor to slow to an average lower speed. Without increasing voltage above rated; the max speed & torque with PWM is the rated value. A DC Motor with Gearhead is another method to increase or decrease speed range and resultant torque.