Chapter 03 · Components
The muscles
Brushless motors turn electricity into thrust. Choosing them well means balancing power, weight, efficiency and smoothness.
How to read the size
The four digits give the size of the stator, the fixed part with the windings: on a 2207, 22 mm in diameter and 7 mm tall. A wider stator gives more torque (quicker speed changes); a taller one gives more rpm. More volume means more power, but also more weight.
| Drone | Common sizes |
|---|---|
| Tiny whoop | 0702–0802 (1S) |
| Toothpick / 2–3" | 1103–1404 |
| 3.5–4" | 1804–2004 |
| 5" | 2207, 2306, 2208 |
| 7" | 2806.5–2807 |
KV and voltage go together
KV is the number of revolutions per minute the motor spins per volt, with no load. Since the final rpm depends on KV × voltage, the more cells your battery has, the less KV you need. You can compare combinations with the rpm calculator.
5" on 6S
Between 1700 and 1950 KV. Less current for the same performance and cooler motors.
5" on 4S
Between 2300 and 2700 KV.
High KV
More punch and speed, but higher consumption, more heat and less flight time.
Low KV
Smoother and more efficient. Ideal for cinematic or long range with big props.
Signs of quality
- Good bearings: the motor spins smooth and quiet when you turn it by hand.
- A titanium or hardened-steel shaft that doesn’t bend on the first crash.
- A sturdy bell, with curved magnets sitting very close to the stator.
- A standard bolt pattern (16 × 16 mm with M3 on a 5") for frame compatibility.
- Similar weight across all four units.
Mounting and maintenance
- Screws with at least 1 mm of clearance to the windings. If they touch them, the motor burns out.
- Spin them by hand now and then: if they grind or feel stiff, check the bearings and clean out the sand.
- Touch them after flying: they should be warm. If they’re too hot to touch, there’s a filter or D-term problem.
- Motor wires protected with heat-shrink tubing under the arm.
A motor that has overheated can lose magnet strength and fail in flight. If one is hotter than the others, find out why.