Understanding RC Electric Motors: Brushed, Brushless, kV, Turns and ESCs
Every RC electric motor turns electrical current into rotation with magnets and copper windings. Brushed motors switch the current with carbon brushes and are cheap and simple; brushless motors switch it electronically in the ESC and are more efficient, more powerful and almost maintenance-free. The numbers on the can tell you how fast it spins: kV is RPM per volt, turns describe the winding, and the can size (like 540 or 3660) tells you how much power it can handle without overheating.
By Kyle HilsonUpdated: October 20264 min read
Brushed vs brushless
| Brushed | Brushless | |
|---|---|---|
| Switching | Brushes and commutator | ESC electronics |
| Efficiency | Lower, more heat | Higher |
| Maintenance | Brushes wear; break-in, cleaning | Bearings only |
| Wires | 2 | 3 (plus sensor cable if sensored) |
| Cost | Low | Higher |
| Typical use | Entry RTRs, crawlers, stock classes | Bashers, racing, speed runs |
Brushed motors benefit from a short break-in; see how to break in a brushed motor.
Sensored vs sensorless
Brushless motors need to know where the rotor is. Sensorless motors work it out from the motor’s back-EMF, which is cheap and robust but can stutter at very low speed. Sensored motors have Hall sensors and a small cable to the ESC, giving smooth starts. Racing and crawling favour sensored; bashing is fine with sensorless.
kV, turns and can size
- kV: unloaded RPM per volt. A 3,500 kV motor on 7.4 V (2S) spins up to about 25,900 RPM before load. Higher kV = more speed, more current.
- Turns (T): used for 1/10 motors. Fewer turns = higher kV. A 17.5T is a mild stock-class motor; a 4.5T is very fast.
- Can size: e.g. 540 (1/10), 550 (longer), 3660/4074 (1/8 and larger). Bigger cans handle more power and heat.
- Poles: 2-pole inrunners for cars rev high; multi-pole outrunners for planes give torque at lower RPM.
Matching motor and ESC
- The ESC must support the motor type (brushed or brushless, sensored if needed).
- Its continuous current rating must exceed what the motor draws under load.
- Check the voltage (LiPo cell count) limits of both motor and ESC.
- Check turn or kV limits: many ESCs list a minimum turn count.
- Calibrate the ESC to the radio and set the battery type; see how to program an RC car ESC.
Gearing and heat
A motor’s speed only becomes car speed through the gearing. A bigger pinion or smaller spur gives more top speed but more load and heat. Check the motor temperature after a few minutes: if you can’t hold your finger on the can for five seconds (roughly above 70–80 °C), gear down. Heat is the main killer of motors, because it weakens the magnets and the winding insulation. Choosing a motor for your car is covered in choosing a brushless motor for an RC car.
Common mistakes
- High-kV motor on high voltage in a heavy car: overheating.
- Ignoring the ESC’s turn limit with brushed motors.
- Wrong phase wiring: the motor runs backwards (swap two wires on a sensorless motor, or set direction in the ESC).
- Never checking temperature after a gearing change.
Looking after a motor
Brushless motors need little care: blow out dust, check that the bearings spin freely and quietly, and keep the sensor cable plugged in firmly. Brushed motors also need the commutator cleaned with motor spray and new brushes when they wear short. In both cases, watch for burnt smells and discoloured windings, which mean the motor has been run too hot.
FAQ
Is higher kV better?
Only for speed on light setups; lower kV gives more torque and runs cooler on high voltage.
Can I put a brushless motor in a brushed car?
Yes, with a brushless ESC and often stronger drivetrain parts.
Why three wires?
Brushless motors have three phases that the ESC energises in sequence.
How hot is too hot?
Above roughly 80 °C on the can; gear down or improve cooling.
More on this topic: the complete RC Cars guide covers the basics behind this article.
About 20 years in RC. Mostly boats in the NAVIGA Mini Eco Expert class, with many self-made parts; also a King Motor Baja 5B, a home-built electric plane, home-built nitro planes he has flown, and an RC helicopter. More about SwellRC
