Brushless Motors

🟢 Start — zero knowledge, plain words. 🟡 Hands-on — building or buying, specifics and tradeoffs. 🔴 Specialist — the physics and math behind it.

🟢 Start. A brushless motor is a spinning "bell" of magnets around a stationary stator of copper coils. Nothing rubs on anything (except bearings), so power and lifespan are in a different league from brushed motors. Read the size from the code: 2207 = stator 22 mm in diameter, 7 mm tall. The other key parameter is KV — how many RPM the motor turns per volt applied (unloaded).

🟡 Hands-on. KV is chosen as a pair with the battery, because the product is what matters: an 1800 KV motor on 6S (~22.2 V) targets similar RPM to 2500 KV on 4S (~14.8 V). Bigger stator = more torque = bigger props: a 5″ freestyle build is typically 2207/2306 at 1700–1950 KV (6S), a 7″ long-ranger runs 2806.5 at ~1300 KV, a whoop spins 0802 at ~20,000 KV (1S). The rule to remember: low KV + big prop = efficiency and lift; high KV + small prop = RPM and snap.

🔴 Specialist. KV hides a torque constant:

$$K_t = \frac{60}{2\pi \cdot KV}\ \left[\frac{\text{N·m}}{\text{A}}\right],\qquad \tau = K_t I,\qquad \text{RPM}_{\text{no-load}} \approx KV\cdot V$$

For 1800 KV: $K_t \approx 5.3$ mN·m/A — current under load is now calculable. Heat losses grow with the square of current ($P_{loss} = I^2R$), which is why an "oversized" stator runs cooler at the same thrust — and overheating weakens magnets permanently. Powertrain thrust grows roughly with the square of RPM — as long as the prop keeps up:

⚠️ Common mistakes: picking KV without looking at the battery cell count; mounting motors with screws that are too long (screw touches windings = short); first flight without checking prop-to-arm clearance.

🖼️ Photos: your own disassembled motor (bell, magnets, stator); "brushless DC motor" animations on Wikimedia Commons.