Formula Used
Kv method: Kt = 60 ÷ (2πKv), then T = Kt(I − I₀).
Acceleration method: T = Jα.
Propeller method: Q = Cqρn²D⁵.
Gear method: Tout = Tmotor × G × ηg.
How to Use
Select the calculation method matching your available motor data. Enter consistent values and verify every selected unit. Review warnings before choosing a motor or propeller combination.
Use realistic efficiency values from reliable test information. Compare several motors under matching operating conditions. Always confirm limits using manufacturer data before actual flight.
Example Data
| Scenario | Power | RPM | Voltage | Current | Motors | Safety factor |
|---|---|---|---|---|---|---|
| Quadcopter climb | 850 W | 6,000 RPM | 22.2 V | 25 A | 4 | 1.25 |
| Heavy-lift hover | 1.2 kW | 4,800 RPM | 44.4 V | 32 A | 8 | 1.40 |
| Racing drone | 600 W | 18,000 RPM | 22.2 V | 38 A | 4 | 1.15 |
Frequently Asked Questions
What does motor torque mean for a drone?
Motor torque describes rotational force at the motor shaft. Higher torque helps turn larger propellers under demanding loads. Always confirm limits using manufacturer data before actual flight.
How does Kv affect motor torque?
Lower Kv motors generally provide more torque per ampere. Higher Kv motors favour speed at comparable voltage levels. Always confirm limits using manufacturer data before actual flight.
Is torque the same as thrust?
Torque rotates the propeller while thrust moves air axially. Propeller geometry converts shaft power into useful flight thrust. Always confirm limits using manufacturer data before actual flight.
Why subtract no-load current?
No-load current covers friction and internal operating losses. Subtraction estimates current producing useful electromagnetic shaft torque. Always confirm limits using manufacturer data before actual flight.
How accurate is the propeller torque method?
Accuracy depends strongly on the selected torque coefficient. Manufacturer tests provide better coefficients for specific propeller models. Always confirm limits using manufacturer data before actual flight.
What safety factor should I use?
Many designs start between 1.20 and 1.50. Heavy payloads and uncertain data require larger margins. Always confirm limits using manufacturer data before actual flight.
Why does altitude reduce performance?
Higher altitude usually means lower surrounding air density. Propellers then generate less aerodynamic force at equal speed. Always confirm limits using manufacturer data before actual flight.
Can this calculator select an ESC?
The current checks help screen basic ESC requirements. Thermal behaviour and transient peaks still need manufacturer testing. Always confirm limits using manufacturer data before actual flight.
Should bench-test values match flight values?
Bench airflow can differ greatly from real flight cooling. Batteries also sag differently during rapid throttle changes. Always confirm limits using manufacturer data before actual flight.