Torque-Speed Curve

扭矩-转速曲线（T-N 曲线）Advanced

A curve plotting the maximum torque a motor can deliver at each speed.

A torque-speed curve has speed on one axis and torque on the other, describing the limits of what a motor can deliver at a given voltage. Torque is highest at low speed; as speed rises, back-EMF (the reverse voltage the motor itself generates as it spins) increasingly cancels out the supply voltage, so less current can flow in, and torque drops accordingly, reaching zero at the no-load speed. The curve is usually split into two zones: a continuous-operation zone, where the motor can run indefinitely without overheating, and a peak zone, usable only briefly. When picking a joint motor, engineers plot the torque and speed a task actually needs — a robot's jump takeoff, a fast leg swing — onto this curve, to check it falls within the motor's capability with some margin to spare.

ExampleWhen designing a quadruped robot, engineers overlay the knee joint's torque-versus-speed trajectory during a jump onto a candidate motor's T-N curve to check it doesn't exceed the peak zone.

Also called: T-N Curve
Related: Stall Torque / No-Load Speed · Peak Torque · Rated Torque · Torque Constant (Kt) · Motor Thermal Derating / Overheat Protection · Power Density (W/kg)
Sources: Motor constants - Wikipedia