Enter Motor, Propeller, Battery, and ESC Data
Example Data Table
| Setup | Kv | Voltage | Prop | Current | Use Case |
|---|---|---|---|---|---|
| Sport trainer | 920 | 14.8 V | 10 x 4.5 | 32 A | Balanced thrust and runtime |
| Fast park flyer | 1400 | 11.1 V | 7 x 5 | 28 A | Higher pitch speed |
| Slow thrust build | 700 | 22.2 V | 13 x 6.5 | 40 A | Larger propeller control |
Formula Used
No-load RPM: Kv × battery voltage.
Loaded voltage: battery voltage × (1 − voltage sag percentage).
Loaded RPM: Kv × loaded voltage × load factor.
Input power: loaded voltage × full throttle current.
Output power: input power × motor efficiency.
Heat loss: input power − output power.
ESC rating: full throttle current × (1 + ESC margin).
Runtime: battery Ah × usable capacity ÷ average current × 60.
Static thrust: Ct × air density × revolutions per second² × prop diameter⁴.
Pitch speed: prop pitch × loaded RPM × 0.001524.
How to Use This Calculator
Enter the motor Kv and battery voltage first. Add the current you expect from a wattmeter or manufacturer table. Use average current for runtime, not peak current. Enter propeller diameter and pitch in inches. Keep the thrust coefficient near 0.08 to 0.12 when no test data is available.
Press Calculate. Read the result above the form. Compare motor load, ESC size, battery C rating, and thrust to weight ratio. Download the CSV for spreadsheet use. Download the PDF for simple build notes.
RC Brushless Motor Planning
An RC brushless motor looks simple, yet it controls many flight limits. Kv, voltage, propeller size, current, and efficiency work together. A small change in prop pitch can raise load quickly. This calculator helps you estimate those changes before bench testing.
Why Motor Matching Matters
A motor should fit the airframe, battery, propeller, and ESC. High Kv motors spin fast and suit smaller props. Lower Kv motors often turn larger props with more torque. The right match improves thrust and reduces heat. It also protects magnets, windings, connectors, and cells.
Power, Current, and Heat
Input power comes from voltage multiplied by current. Only part of that power becomes shaft output. The rest becomes heat. Efficiency is therefore a key warning value. If current is near the motor limit, use a smaller prop, lower pitch, or lower voltage. Always leave a safety margin.
Propeller Effects
Propeller diameter and pitch affect load strongly. Bigger diameter usually increases thrust, but it also increases current. Higher pitch can raise speed, but it may overload the motor. The thrust estimate in this page is an approximation. Real thrust depends on blade design, air density, prop condition, and test stand accuracy.
Battery and Runtime
Battery capacity controls possible runtime. Usable capacity is lower than the printed value because cells should not be fully drained. The calculator uses a usable capacity percentage. It also compares average current with discharge capability. This helps show whether the pack is working too hard.
ESC Sizing
An ESC should not match the exact calculated current. It needs headroom for bursts, hot weather, poor cooling, and aggressive throttle changes. The ESC recommendation adds a margin. More margin is usually safer when space and weight allow.
Practical Use
Use this tool before buying parts or changing propellers. Enter conservative values first. Compare two or three setups using the example table style. Then confirm results with a wattmeter and short ground run. Stop testing if parts become hot, vibrate, or make unusual sounds. Calculations guide setup choices. Real testing confirms them.
Safety Reminder
Logs from flights help refine estimates. Note prop size, battery age, peak current, motor temperature, and wind. Better records make future upgrades safer, easier, and clearer too.
FAQs
What does motor Kv mean?
Kv means RPM per volt with no load. A 920 Kv motor can spin near 920 RPM for each volt before propeller load, voltage sag, and losses reduce speed.
Why is loaded RPM lower?
The propeller resists rotation. Battery voltage also sags under current. The calculator combines load factor and sag to estimate a more realistic RPM.
Should ESC rating equal motor current?
No. Add margin for bursts, airflow loss, heat, and throttle changes. A larger ESC is usually safer if weight and space are acceptable.
Is the thrust result exact?
No. It is an estimate based on air density, RPM, diameter, and thrust coefficient. Use a thrust stand for exact propeller testing.
What current should I enter?
Use full throttle current from a wattmeter when possible. If unavailable, use motor data for the same propeller, voltage, and cooling setup.
How is flight time estimated?
It divides usable battery capacity by average current. It does not assume full throttle all flight. Real time changes with throttle style.
What is a safe prop tip speed?
Lower tip speed is quieter and more efficient. Very high Mach values may cause noise, vibration, and efficiency loss on many RC propellers.
Can I use this for drones?
Yes, for rough motor and propeller planning. Multirotors need total thrust from all motors, hover current, frame drag, and controller tuning checks.