BLDC Motor
Brushless DC Motor
A permanent-magnet rotor chased by electronically switched stator coils — a 'DC motor' with the commutator replaced by a controller. Powers drones, e-bikes, EVs, ceiling fans and every cooling fan on a PCB.
Schematic symbol
Motor
How bldc motor appears in a circuit diagram.
Types & variants
Key specs
KV rating
RPM/VNo-load speed per volt. A 1000 KV motor on 11.1 V spins ~11,100 RPM. Low KV = more torque per amp, for bigger props/wheels.
Rated voltage
V / cells (S)Often given as LiPo cell count: 2S–6S hobby, 36/48 V e-bikes, 300–800 V EVs.
Max current
AContinuous current the windings tolerate; the ESC must be rated above it.
Torque constant
N·m/ATorque per amp — inversely related to KV. Industrial datasheets quote this instead of KV.
Pole/slot count
—E.g. 12N14P outrunner. More poles = smoother low-speed torque, lower top speed.
Markings
Hobby motors are named by stator size and KV, e.g. '2212 920KV' (22 mm dia × 12 mm high stator). Three thick phase wires (any colour); sensored motors add a 5–6 pin Hall connector.
Standard values
Drone: 2204–2306 outrunners, 1700–2600 KV on 4S. E-bike hubs: 250 W–1500 W at 36/48 V. PC fans and BLDC ceiling fans: integrated controller, just DC or mains in.
How to choose
1) Pick KV and voltage so no-load RPM suits the prop/wheel. 2) Size continuous current with 30% headroom, then choose an ESC rated above it. 3) Sensored (or FOC sensorless) for smooth start from standstill under load — e-bikes, gimbals; plain sensorless is fine for props and fans. 4) Outrunner for torque at low speed, inrunner for high RPM.
Pinout & package
Three phase wires to the ESC — swap any two to reverse direction. Sensored versions add Hall wires (5 V, GND, HA, HB, HC). Mounting: M2/M3 bolt circles on hobby motors, face or hub mounting on e-bike and industrial units.
Example circuits
- Quadcopter: flight controller → 4 ESCs → 4 outrunners
- E-bike: 48 V battery → sensored controller → hub motor with PAS sensor
- BLDC ceiling fan: mains → SMPS + controller board → 12–24 pole motor (half the power of induction fans)
- Sensorless pump/fan drive using back-EMF zero-cross detection
Common failures
Burnt windings from overcurrent (blackened, shorted turns), demagnetised rotor from overheating (speed rises, torque falls), failed Hall sensor (cogging, won't start smoothly), bearing wear from prop crashes, and shorted phase from crushed wire insulation.
How to test
Spin by hand: you should feel uniform magnetic cogging and no grinding. Measure the three phase-to-phase resistances — they must match (fractions of an ohm). Shorting any two phases should make hand-spinning noticeably harder (back-EMF braking). Check Hall outputs toggle 0/5 V as the shaft rotates.
Substitutes
Match KV, size and voltage for hobby swaps. A PMSM with FOC is the industrial equivalent. Brushed DC can substitute only where cheap simple control matters more than lifespan; induction motors replace BLDC at mains-powered fixed-speed jobs.