Torque-speed curves across motor families
Brushed DC motors deliver constant torque as speed rises until base speed, then torque drops as back-EMF builds. This makes them ideal for applications needing sustained high torque at variable speed, like drill chucks and vehicle traction. Induction motors (AC three-phase) start with high induction torque and then drop as speed increases toward synchronous speed. Synchronous motors lock to the line frequency and run at exactly that speed; they are more efficient but less flexible. Stepper motors deliver precise angular position steps but have low continuous torque. Brushless DC motors, driven by electronic commutation, offer efficiency and wide speed range, now dominant in fans and tools.
Choosing the motor for load requirements
High-inertia loads (like centrifuges) that start from rest need motors with strong starting torque; induction motors excel here. Variable-speed loads (like conveyor speed adjustment) suit brushed or brushless DC because torque stays high across the speed range. Constant-speed applications (like refrigerator compressors) choose synchronous or carefully controlled induction motors to run efficiently at one point on the curve. Stepper motors suit precision positioning where torque demand is low and speed steps are desired (printers, 3D printers). The efficiency and cost tradeoff varies by motor type and duty cycle.