Choosing a brushless motor and ESC: kV, turns, amps and cell count

Whether you are converting a model from brushed to brushless, replacing a faulty drive or simply want more power: motor and ESC have to match each other, the battery and the model. A few key figures narrow the choice down quickly. New to the hobby? Then start with the guide RC car for beginners.

Brushed or brushless?

Brushed motors are simple, cheap and easy to control at very low speed. That is why they are still common in crawlers and entry-level models. Their carbon brushes wear, however, and they are less efficient.

Brushless motors work without brushes. They are more efficient, more powerful and almost maintenance-free; only the ball bearings wear. They always need a brushless ESC; a brushed ESC will not work with them.

Motor size: which motor fits which model?

The size of a brushless motor is usually part of its name: the first two digits are the diameter, the following ones the length in millimetres. A 3652 motor is 36 mm in diameter and 52 mm long. A longer motor of the same diameter delivers more torque.

The shaft diameter also differs by size, and the bore of the pinion has to match it exactly. You will find the usual sizes in the guide How to calculate RC gear ratio.

What does kV mean on a motor?

The kV rating states how many revolutions per minute the motor makes per volt without load. A 3300 kV motor on a fully charged 2S pack (8.4 V) therefore spins at about 27,700 rpm unloaded, on 3S (12.6 V) at about 41,600 rpm.

A high kV rating does not automatically mean more power. It means more rpm, and with the same gearing more current and more heat. Hence the most important rule of thumb: the higher the voltage, the lower the kV should be. Manufacturers state limits for this. For the Hobbywing QuicRun WP10BL60 G2, for example, motors of size 3652 and 3660 are approved up to 6000 kV on 2S, but only up to 3500 kV on 3S. Light vehicles on smooth surfaces tolerate higher kV than heavy trucks off-road.

Turns: the rating of racing and brushed motors

Sensored racing motors in 540 size are often rated by the number of winding turns (T) instead of kV. Fewer turns mean more rpm. Many racing classes prescribe the number of turns, for example 13.5T or 17.5T in stock classes. For orientation, the values of the Hobbywing Xerun Justock motors:

The same applies to brushed motors: more turns mean lower rpm and finer control, typical for crawlers.

Sensorless, sensored or FOC?

• Sensorless (“SL” at Hobbywing): the ESC detects the rotor position through the motor wires. Robust, inexpensive and insensitive to water and dirt, ideal for bashers, short course trucks and monster trucks. When starting off under heavy load, the motor may cog slightly.

• Sensored (“SD”): an additional sensor cable reports the rotor position. This gives a particularly smooth start and fine control at low rpm. Standard in racing and in large, heavy vehicles.

• FOC (field-oriented control): the ESC drives the motor with a sinusoidal signal. The result is very smooth running at walking pace, and the vehicle holds reliably on a slope. That is why FOC is used mainly in crawlers, for example in the Hobbywing Fusion and AXE systems.

The ESC: continuous current, cell count, BEC

• Continuous current (A): the bigger and heavier the model and the higher the voltage, the more current flows. Allow some headroom, because an ESC that runs at its limit all the time gets hot and shuts down. In 1:10, 60 to 120 A is common; in 1:8, considerably more.

• Cell count: the permitted cell count is in the data sheet, for example “2S–3S” or “3S–6S”. A pack with more cells than permitted destroys the ESC.

• BEC: the built-in power supply of the ESC feeds the receiver and the steering servo. Voltage and current both matter. Many Hobbywing ESCs can be switched between 6.0 V and 7.4 V; select 7.4 V only if servo and receiver are designed for it. Powerful servos need a strong BEC, more in the guide Choosing and setting up a steering servo.

• Water resistance: ESCs with “WP” in their name (waterproof) are protected against splashes, puddles and snow. They should still not be submerged.

Combos: matched motor and ESC

If you would rather not compare parts at length, choose a combo of motor and ESC matched by the manufacturer. An overview from our range:

Individual parts are listed under motors and speed controllers.

Example: a brushless system for a 1:10 RC car

For a 1:10 2WD short course truck or buggy on 2S or 3S, a sensorless 3652 motor with a water-resistant ESC of around 60 A is a good fit. If you want to run both 2S and 3S, watch the kV limit for 3S: for the QuicRun WP10BL60 G2 it is 3500 kV. The combo of WP10BL60 G2 and 3652SL motor with 3250 kV stays below that and therefore suits both 2S and 3S. For heavy 4WD short course trucks and monster trucks on 3S, the stronger QuicRun WP10BL120 G2 is the better choice.

Setting up a brushless ESC: calibration and programming

1. Calibrate the throttle range: after installation, after changing the transmitter or after adjusting the throttle trim, the ESC has to learn neutral, full throttle and full brake again, usually via the SET button (see the manual). First set the throttle trim on the transmitter to 0 and the throttle travel to 100%.

2. Battery type and low-voltage cutoff: set to LiPo so that the ESC cuts power in time. More in the guide Charging and storing LiPo batteries.

3. Running mode: forward/brake for racing, forward/reverse/brake for everyday driving, direct forward/reverse for crawlers.

4. Brake, drag brake and punch: the drag brake (automatic holding brake) brakes as soon as you release the throttle. On crawlers it is important so that the vehicle stays put on a slope. Punch determines how hard the motor accelerates; on slippery surfaces, set it lower.

5. Timing: increase only in small steps while checking the temperature. More timing means more rpm, but also more heat.

Depending on the ESC, settings are made with the SET button, an LED program box or the LCD program box Pro, which supports Xerun, Ezrun and selected QuicRun ESCs such as the WP10BL60 G2. Selected Xerun and Ezrun ESCs can also be set up wirelessly with the OTA Bluetooth module and the “HW Link” app.

Checking the temperature

Measure motor and ESC after three to five minutes of driving, most easily with an infrared thermometer. If the motor is too hot, the gearing is usually too tall, and a smaller pinion helps. Limits and the step-by-step procedure are in the guide How to calculate RC gear ratio.