For applications where variable speeds are necessary, typically an AC motor with an Inverter or brush motors are used. Brushless DC motors are an advanced option due to their wide speed range, low heat and maintenance-free operation. Stepper Motors offer high torque and smooth low speed operation.
Speed is typically controlled by manual operation on the driver or by an external switch, or with an external 0~10 VDC. Speed control systems typically utilize gearheads to increase output torque. Gear types range from spur, worm or helical / hypoid depending on torque demands and budgets.