motorspeed

Motor speed is the rate at which a motor’s output shaft rotates, typically expressed in revolutions per minute (rpm) or radians per second (rad/s). It is a central parameter that determines how a motor performs under a given load, often described alongside torque. No-load speed refers to the speed with almost no load, while stall speed is the point at which the motor cannot deliver any rotational motion because the torque required exceeds the motor’s capability.

Different motor types exhibit distinct speed characteristics. Direct-current (DC) motors have speed that is approximately proportional to the applied voltage for a given torque; increasing load decreases speed. Brushless DC motors (BLDC) behave similarly but are driven by electronically commutated, PWM-controlled waveforms. Three-phase AC motors, such as induction and synchronous motors, operate differently: induction motors run at a slip below the synchronous speed set by the supply frequency and the number of poles, while synchronous motors lock to the exact synchronous speed, barring overload or faults.

Control methods vary by application. Open-loop speed control uses fixed voltage or frequency without feedback, while closed-loop control employs sensors (tachogenerators or encoders) and a controller to maintain a target speed. For DC and BLDC motors, speed is often controlled with PWM to regulate average voltage. For AC motors, variable frequency drives (VFDs) adjust frequency and voltage (often with V/Hz control) to achieve desired speed across a range while preserving torque. Some systems use gearing to achieve required shaft speed.

Performance considerations include regulation, efficiency, heat generation, and dynamic response, all influenced by design, load, and control strategy. Applications span industrial drives, robotics, consumer appliances, and transportation.