Rate of Fire estimator
Motor under load: — RPM
What Is Rate of Fire?
Rate of fire is how many BBs an AEG cycles per second (RPS) or per minute (RPM). It is decided entirely by how fast the motor spins the gears under load. This calculator estimates RPS from your battery voltage, motor RPM/V rating, gear ratio and a load-efficiency figure, then converts it to RPM and shows the motor speed under load.
What Controls ROF
- Battery voltage — higher voltage spins the motor faster. Going from 7.4 V to 11.1 V is the single biggest ROF jump.
- Motor RPM/V (Kv) — a high-speed motor turns more revolutions per volt; a torque motor turns fewer but pulls harder.
- Gear ratio — lower ratios (e.g. 13.79:1) trade torque for speed; higher ratios (18.75:1) favour torque and a stronger spring.
- Load efficiency — the spring, air seal and friction mean the gearbox never hits the motor’s free-spin speed, so a realistic 70–85% is applied.
Rate of Fire by Voltage & Gears
Estimated RPS for a 3000 RPM/V motor at 80% load efficiency, across common voltages and gear ratios:
| Battery | 18.75:1 (torque) | 16:1 (balanced) | 13.79:1 (speed) |
|---|---|---|---|
| 7.4 V (2S) | 15.8 RPS | 18.5 RPS | 21.5 RPS |
| 11.1 V (3S) | 23.7 RPS | 27.8 RPS | 32.2 RPS |
| 14.8 V (4S) | 31.6 RPS | 37.0 RPS | 42.9 RPS |
Use these as a baseline. A fresh battery and a light spring push the real number higher; a heavy spring or weak motor pull it lower.
Voltage, Gears or Motor?
There is more than one way to raise ROF, and they are not equal:
- More voltage is the easiest gain, but it stresses the gearbox, piston and contacts — high ROF needs a MOSFET and good shimming.
- Speed gears raise ROF without more voltage, but cost trigger response and torque, so they suit lighter springs.
- A high-speed motor raises ROF but draws more current and can struggle with a strong spring.
For a durable build, match a sensible voltage and gear ratio to your spring rather than chasing the highest possible RPS.
Why Real ROF Is Lower Than Theory
The free-spin motor speed is never reached in a built gun. The spring resists every cycle, the air seal adds load, and the battery sags under high current. That is what the load-efficiency setting accounts for — drop it for a heavy spring or a tired battery, raise it for a light, well-tuned build.
How to Use This ROF Calculator
- Select your battery voltage (2S, 3S, 4S or NiMH).
- Enter the motor RPM/V — check the motor’s spec, typically 2,000–4,000.
- Choose your gear ratio.
- Set a realistic load efficiency (70–85% for most builds) and read RPS, RPM and motor speed.