Motor Efficiency Engineering: Torque, KV Scaling & Thermal Dynamics

Brushless FPV motors operate on electromagnetism. The torque $T$ generated by a stator is directly proportional to stator volume ($V = \pi \cdot r^2 \cdot h$), magnetic flux density $B$, and current $I$:

$$T \propto V \cdot B \cdot I$$

Increasing stator volume (e.g. from 2207 to 2306.5) shifts the torque curve, giving the multirotor more control authority over aggressive propellers.

The KV rating defines the motor's RPM per volt under zero load.

• Fewer Windings (High KV): Thick copper wire, low resistance, high current draw, extreme top-end speed, low torque.
• More Windings (Low KV): Thin copper wire, higher resistance, lower current draw, high torque.

2.1 4S vs 6S Scaling Dynamics

Running a lower KV motor (e.g. 1750KV) on 6S ($22.2\text{V}$) draws fewer amps for the same wattage output compared to a 2400KV motor on 4S ($14.8\text{V}$), lowering ohmic losses:

$$P_{loss} = I^2 \cdot R$$

Excessive current draw leads to thermal loading. If stators exceed $150^\circ\text{C}$, the neodymium magnets (typically N52SH grade) undergo irreversible demagnetization, causing permanent torque loss.