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Motor Comparison

Motor Type / Characteristics / Commutation / Brushes / Starting Torque
Stepper / Precise speeds and positions; holding torque equal to starting torque; relatively low speed (500 rpm typical); easily bidirectional. / External; electronic. Digital by definition. Usually allows full and half-steps, CW or CCW. / No / Very high; equal to maximum torque
DC Brushless / Precise speeds; holding torque equal to starting torque; very wide speed range; easily bidirectional / External; electronic. Analog by definition. / No / Very high; equal to maximum torque
DC PM / Excellent starting torque; can be made very small and relatively inexpensive; very high efficiency / On armature / Yes / Very high; equal to maximum torque
Universal / Excellent starting torque; can run off DC or AC power; excellent power/weight ratio; low efficiency / On armature / Yes / Very high; equal to maximum torque
Single-phase AC Induction (capacitor-start or shaded pole) / Very rugged; inexpensive; relatively constant speed / Via AC induction; depends on AC frequency. / No / Very low; cannot start its rated load.
3-phase AC Induction / Extremely high efficiency and power/weight ratio / Via 3-phase AC induction; depends on AC frequency / No / Very high; equal to maximum torque
AC Synchronous / Very constant rpm / Via AC power; depends on AC frequency. / Yes / None; needs some way to bring up to synchronous speed

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Motor Comparison

Motor Type / Efficiency / Speed Control / Holding Torque / Typical Size Range
Stepper / Very low; typically <20% / Outstanding; digitally controlled. Acceleration and deceleration curves more complicated but common. / Excellent; equal to maximum torque / Small to medium (1 oz-in to 100 oz-in); not rated in hp.
DC Brushless / Very high; typically 75%-95% / Outstanding; digitally/electronically controlled. / Excellent; equal to maximum torque / Small to medium; some large (1/20 hp to 1 hp; some to 500 hp.)
DC PM / Very high; typically 60%-90% / Poor; fair with Va method. With servo feedback, absolutely outstanding. / None / Small to medium; some large (1/50 hp to 1 hp; some to 500 hp.)
Universal / Relatively poor; typically 20%-60% / Poor; fair with Va method. Not usually used where specific speed is important / None / Small to medium (1/10 hp to 5 hp)
Single-phase AC Induction (capacitor-start or shaded pole) / Very high; typically 80%-90% / Fair depending on load variation. With servo feedback, absolutely outstanding. / None / Small to medium (1/10 hp to 5 hp)
3-phase AC Induction / Very high; typically 85%-98% / Good, depending on load variation. / None / Medium to very large (5 hp to 5000 hp)
AC Synchronous / Very high; typically 90%-98% / Outstanding, as long as load does not prevent synchronous operation. / None / Small to medium (1/20 hp to 5 hp)

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Motor Type / Typical Application / Role of CEMF / Impact of Stalling / Impact of Varying Va
Stepper / Positioning: floppy disk drive head positioner / None / None / Varies torque
DC Brushless / Precise rpm: hard disk drive spindle motor / None / None / Varies torque
DC PM / DC: cars, portable tools, RC cars / Limits maximum RPM / Burns out motor / Varies RPM
Universal / Power/weight ratio: corded hand tools / Limits maximum RPM / Burns out motor / Varies RPM
Single-phase AC Induction (capacitor-start or shaded pole) / Small AC: fan/blower, refrigerator compressor, washing machine / Minimal / Minimal / Varies torque
3-phase AC Induction / Big movers: Large industrial pumps, blowers / Minimal / Overheats motor relatively slowly / Varies torque
AC Synchronous / Synchronicity: clocks, timers, synchronous drives / Minimal / Minimal / Varies torque