The electronic speed controller, or ESC, connects the battery, motor, receiver, and often the servos. Choosing and setting it up correctly is essential for reliable electric flight.
What an ESC does
An ESC meters power from the battery to a brushless motor in response to the throttle signal. It also provides low-voltage protection and may include a battery eliminator circuit (BEC) that powers the receiver and servos.
Choosing the correct ESC
- Current rating: Select an ESC rated above the measured full-throttle current. A practical margin helps with hot weather, aggressive flying, and manufacturing variation.
- Voltage rating: The ESC must support the battery cell count.
- BEC rating: Confirm the BEC can supply the number, size, and type of servos in the airplane.
- Cooling: Install the ESC where air can move around it without allowing wires to contact rotating parts.
Use a wattmeter to check the complete motor, propeller, battery, and ESC combination. Propeller changes can raise current dramatically.
Linear and switching BECs
A linear BEC is simple but creates more heat as battery voltage and servo load increase. A switching BEC is generally more efficient and better suited to higher cell counts or heavier servo loads. Large models may use a separate receiver battery or external BEC.
Basic wiring
- Connect the three motor wires to the ESC.
- Connect the ESC’s receiver lead to the throttle channel with correct polarity.
- Connect the battery only when the transmitter is on, throttle is low, and the model is restrained.
- Swap any two motor wires if the motor rotates the wrong direction.
Remove the propeller before changing throttle calibration, brake settings, motor timing, or rotation.
Common settings
- Brake: Often off for sport models; useful for folding propellers.
- Low-voltage cutoff: Protects the battery, but should not replace a flight timer.
- Timing: Start with the motor manufacturer’s recommendation.
- Throttle calibration: Teaches the ESC the transmitter’s throttle range.
Troubleshooting
Repeated beeping commonly indicates that the ESC is waiting for a valid throttle signal, detecting the wrong throttle position, or reporting battery status. A hot ESC suggests excess current, poor cooling, a heavy servo load, or a component problem. Stop and investigate rather than flying again.
Related guides: electric motors, propellers, and troubleshooting.