Motors & Propellers

What KV means

A motor's KV rating is its (unloaded) RPM per volt of applied voltage:

$$\text{RPM}_\text{no-load} \approx K_V \times V$$

So a $1900\,KV$ motor on a fully charged 6S pack (nominal $22.2\ \text{V}$, ~$25.2\ \text{V}$ charged) spins up to roughly $1900 \times 25.2 \approx 47\,900\ \text{RPM}$ with no prop attached. Under a real propeller load the actual RPM is substantially lower, but KV still tells you the family of speed you're working in.

Pack	Typical motor KV (5″)	Idea
4S	2400 – 2700	More KV to reach useful RPM
6S	1700 – 1950	Lower KV, lower current draw

The 6S trend in modern 5″ builds is mostly about current: for the same power, higher voltage means lower current, which means less heat in the ESC and thinner, lighter wiring.

Prop pitch

A propeller labelled 5.1 x 3.1 x 3 is 5.1″ diameter, 3.1″ pitch, 3 blades. Pitch is the ideal forward distance per revolution. Ideal (no-slip) top speed is:

$$v_\text{ideal} = \text{RPM} \times \text{pitch} \times \frac{1}{60}$$

(with pitch converted to meters). Real props "slip", so true speed is lower — but higher pitch trades low-end grip for more top speed, while lower pitch gives crisper, more responsive handling at the cost of straight-line speed.

Pairing rule of thumb

• More blades / more pitch → more thrust and grip, more current, more heat.
• Fewer blades / less pitch → more efficiency and speed, cooler running.

Match the prop to the motor's thermal headroom: if motors are hot to the touch after a pack, you're over-propped for that KV and voltage.