Motor Velocity Constant (KV Rating)

How many more RPM a motor spins at no load for each extra volt applied.

The KV rating is the most commonly quoted spec for a brushless motor, in units of rpm/V: a motor rated KV100 connected to 24V spins at roughly 2,400 rpm with no load. It's roughly inversely proportional to the torque constant (Kt, the torque produced per amp of current), with a common estimate of Kt ≈ 9.55 / KV (N·m/A). So a lower-KV motor produces more torque for the same current, at a lower speed, while a higher-KV motor does the opposite. Drones and RC models want high speed, so they typically use high-KV motors; robot joints want low speed and high torque, so they typically use large-diameter, low-KV outrunner motors paired with a low-ratio reducer. When choosing a motor, KV needs to be considered together with supply voltage, target speed, and gear ratio.

ExampleA KV100 motor connected to a 24V supply spins at roughly 2,400 rpm with no load; by the estimation formula, its torque constant is about 0.095 N·m/A.

Also called

KV, KV Rating, Velocity Constant

Related

Torque Constant (Kt) · Outrunner Motor · Brushless DC Motor · Torque-Speed Curve · Quasi-Direct Drive · Gear Ratio

Sources

Motor constants - Wikipedia