2024.8.3 4:55

By 김민준

The most common motor type used in drones are BLDC motors, which stand for BrushLess Direct Current motors. The name originates from a older technology of motors which are Brushed DC motors.

Brushed DC motors -

• Still used in cheap toy grade drones, often referred as Coreless motors. Brushed motors have short lifetimes and lower efficiency, but are cheap and lightweight, and does not require specialized controllers as it just requires DC power to run, and reversing the polarity will reverse the motor direction.

BLDC Motors - Construction

• Comprised of a Stator(electromagnet), and rotating permanent magnets

• Stator size and dimensions impact motor characteristics, along with the magnet type and shape used in the rotor.

• Powered by 3 phase ‘AC’. Requires BLDC controllers

• Can be reversed by swapping 2 of the 3 wires

• BLDC Outrunner

  • Used in Multirotors or Fixed Wing Propulsions. Outer shell rotates

    • Has higher torque and usually better cooling than inrunners, but the rotating outer shell may cause issues.

    

• BLDC Inrunner

  • Commonly used in RC Cars. Inner shaft rotates

    • Has higher RPM and can be packed more densly, but cooling and torque may suffer

    

• Motor Size

  • Commonly shown as 2207, 3515, 4116, etc.
    • First two number is the stator diameter, while the next two are stator height
    • Taller stators tend to have higher peak RPM and more torque in higher RPM ranges but at the cost of increased power consumption. In terms of feel while flying, taller motors have more punch and ‘resolution’ or control in the upper throttle ranges.
    • Wider stators tend to have higher low RPM torque and better efficiency but lacks in peak RPM. In terms of feel, they are smoother and have more ‘resolution’ or control in the low to middle throttle ranges.

• Motor KV

  • KV is RPM/Volt. It essentially explains how fast the motor will spin
  • Typically smaller the motor or lower the power, the higher it’s KV

• Other specs

  • Thrust, Power, Amps, recommended prop is usually shown in a thrust test chart