Pcb-designHow-ToBeginner · 4 min read

How to Select Motor for Drone: Key Factors and Example

To select a motor for a drone, calculate the required thrust based on the drone's weight and desired flight performance, then choose a motor with a suitable KV rating and power that matches this thrust. Use the motor's specifications and propeller size to ensure efficient and stable flight.

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Syntax

When selecting a drone motor, consider these key parameters:

Thrust: The lifting force the motor can provide, usually in grams or Newtons.
KV Rating: Motor speed constant, indicating RPM per volt.
Power: Maximum wattage the motor can handle.
Propeller Size: The size of the propeller the motor supports.

Basic formula to estimate thrust needed per motor:

Required Thrust per Motor = (Total Drone Weight * Safety Factor) / Number of Motors

python

def calculate_required_thrust(drone_weight_grams, motors_count, safety_factor=1.2):
    return (drone_weight_grams * safety_factor) / motors_count

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Example

This example calculates the required thrust per motor for a quadcopter drone weighing 1200 grams and selects a motor based on that thrust.

python

def calculate_required_thrust(drone_weight_grams, motors_count, safety_factor=1.2):
    return (drone_weight_grams * safety_factor) / motors_count

# Drone specs
weight = 1200  # grams
motors = 4

required_thrust = calculate_required_thrust(weight, motors)

print(f"Required thrust per motor: {required_thrust:.2f} grams")

# Example motor specs (from datasheet)
motor_kv = 920  # RPM per volt
motor_max_power = 200  # watts
motor_max_thrust = 600  # grams

if motor_max_thrust >= required_thrust:
    print("Motor is suitable for the drone.")
else:
    print("Motor is NOT suitable for the drone.")

Output

Required thrust per motor: 360.00 grams Motor is suitable for the drone.

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Common Pitfalls

Common mistakes when selecting drone motors include:

Choosing motors with insufficient thrust, causing poor lift and unstable flight.
Ignoring the KV rating, which affects motor speed and efficiency.
Not matching motor power with battery and ESC (Electronic Speed Controller) limits.
Using propellers that are too large or too small for the motor, reducing performance.

Always check motor datasheets and test with your drone's weight and battery setup.

python

def wrong_motor_selection():
    # Motor thrust less than required
    required_thrust = 400
    motor_thrust = 300
    if motor_thrust >= required_thrust:
        return "Motor is suitable"
    else:
        return "Motor is NOT suitable"

print(wrong_motor_selection())

Output

Motor is NOT suitable

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Quick Reference

Parameter	Description	Typical Range / Notes
Thrust	Force motor can lift	At least 2x drone weight divided by motor count
KV Rating	RPM per volt	Lower KV for bigger props, higher KV for smaller props
Power (Watts)	Max motor power	Match with battery and ESC ratings
Propeller Size	Diameter and pitch	Match motor specs for efficiency

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Key Takeaways

Calculate required thrust per motor based on drone weight and safety margin.

Select motors with thrust ratings above the required thrust for stable flight.

Match motor KV rating and power with your propeller size and battery specs.

Avoid undersized motors to prevent poor lift and flight instability.

Always verify motor specs with datasheets and test in real conditions.