Enter RC Power System Details
Example Data Table
| Model Type |
Cells |
Motor kV |
Current Per Motor |
Suggested Margin |
Likely ESC Range |
| Trainer airplane |
3S |
1100 |
22 A |
25% |
30 A |
| Sport airplane |
4S |
920 |
38 A |
30% |
50 A |
| Quad drone |
6S |
1750 |
42 A |
25% |
60 A |
| RC boat |
6S |
1800 |
95 A |
35% |
150 A |
Formula Used
Pack voltage: cell count × nominal volts per cell.
Loaded voltage: pack voltage × (1 − voltage sag ÷ 100).
Required ESC rating: full throttle current × (1 + safety margin ÷ 100).
Total full current: current per motor × motor count + accessory current.
Input power: adjusted loaded voltage × current per motor × motor count.
Battery C demand: total full current ÷ battery capacity in amp hours.
Flight time: usable amp hours ÷ estimated average current × 60.
Loaded RPM estimate: motor kV × adjusted voltage × 0.8.
Pitch speed: prop pitch in meters × loaded RPM × 60 ÷ 1000.
How to Use This Calculator
Enter the number of motors and battery cell count first. Add the cell voltage used by your pack type. Most LiPo packs use 3.7 volts nominal per cell.
Enter battery capacity, usable capacity, and C rating. Then add the motor kV, prop size, measured current, and motor current limit.
Use watt meter data for full throttle current when possible. It gives a safer result than a simple guess.
Add the throttle value expected during normal driving, flying, or boating. This value is used for runtime only.
Press the calculate button. Read the required ESC rating, recommended common ESC size, C demand, power, heat, and runtime estimate.
Why ESC Sizing Matters
An RC power system works best when every part shares the load. The motor asks for current. The battery supplies it. The ESC controls it. A weak controller may overheat, cut power, or fail during a climb. A controller with enough headroom runs cooler and gives smoother throttle response.
What This Calculator Checks
This calculator estimates the required ESC rating from motor current, throttle use, burst demand, and safety margin. It also checks battery voltage, total current for multi motor builds, watts, watt hours, expected flight time, C rating demand, and current per controller. These values help compare airplanes, drones, boats, cars, and experimental models.
Choosing Sensible Inputs
Use measured current when possible. A watt meter is better than a guess. Prop diameter, prop pitch, gearing, hull drag, tire size, and aircraft weight can change current quickly. Motor kV does not set current alone. It shows speed per volt with no load. The prop or drivetrain creates the real load.
Reading the Results
The required ESC rating is the calculated current after margin. Choose the next common ESC size above that value. The burst rating should exceed short acceleration or takeoff current. Battery C demand shows how hard the pack must work. High C demand means more heat and voltage sag. Flight time is an estimate because throttle changes during real use.
Practical Safety Notes
Keep cooling airflow around the controller. Do not seal it inside foam without a vent. Check connector ratings. Use wires that match current. Test with the model secured. Start with short runs and touch test for heat. Stop if the ESC, motor, battery, or connector becomes too hot.
Better Build Planning
A reliable RC setup is not built from one number. Compare motor limits, ESC limits, battery limits, and real testing. Leave margin for hot days, old packs, heavy props, and long climbs. The calculator gives a planning baseline. Final choices should still follow manufacturer ratings and careful bench tests.
When to Recheck
Recheck the numbers after any prop, gearing, cell count, tire, wheel, fan, or hull change. Small changes can raise current a lot. Record each test, pack temperature, and runtime. Good notes make the next setup faster and safer.
FAQs
What ESC size should I choose?
Choose an ESC equal to or above the calculated recommended size. It should also match battery voltage, connector rating, cooling needs, and the motor maker’s current limits.
Is full throttle current the same as average current?
No. Full throttle current is the peak steady draw during a hard run. Average current is lower for mixed throttle use. Runtime depends mostly on average current.
Why does the calculator use a safety margin?
A safety margin helps cover heat, prop changes, old batteries, poor airflow, and current spikes. Many RC builds use 20% to 35% headroom.
Can I use motor kV to find current exactly?
No. Motor kV helps estimate RPM. Current depends on prop load, gearing, vehicle drag, voltage, motor design, and setup conditions.
What does battery C demand mean?
Battery C demand shows how hard the pack is being discharged. A high value means more stress, heat, voltage sag, and shorter battery life.
Should burst rating be trusted?
Burst rating is useful for short spikes only. Continuous rating is more important for safe sizing. Use good cooling and avoid long burst loads.
Why is my real flight time different?
Real runtime changes with throttle, wind, weight, prop choice, battery age, temperature, and driving style. The calculator gives a planning estimate.
Can this calculator be used for boats and cars?
Yes. Enter measured full throttle current and realistic average throttle. Boat and car loads can be heavy, so use extra margin and careful testing.