Stall Torque / No-Load Speed

A motor's maximum torque when jammed still, and its top speed with no load attached.

These are the two endpoint values on a motor or servo's spec sheet. Stall torque is the torque a motor can output when its output shaft is locked and its speed is zero — the theoretical maximum. No-load speed is the highest speed it reaches with nothing attached. For a DC motor, torque and speed roughly fall along a straight line running from the stall point to the no-load point (the torque-speed curve), and the actual operating point sits somewhere between the two. Current, and therefore heat, is highest at stall, and prolonged stalling can burn out the motor — so selecting a motor by stall torque alone is a mistake; rated torque and sustained-operation capability matter too.

ExampleWhen picking a servo for a robot arm joint, the torque actually needed is usually only a small fraction of the stall torque, leaving margin for acceleration and heat.

Also called

Locked-Rotor Torque, Free-Run Speed

Related

Torque-Speed Curve · Peak Torque · Rated Torque · Servo (Smart Serial Bus Servo) · Motor Thermal Derating / Overheat Protection · Torque Constant (Kt)

Sources

Stall torque - Wikipedia
ROBOTIS e-Manual: XL330-M288-T specifications