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Nitro Helicopters

Rotorflight's NITRO governor flies nitro and petrol helicopters: the flight controller drives the throttle servo and holds the headspeed from an RPM sensor.

Danger

An engine can't be stopped by disarming as quickly as an electric motor. Make sure Motor Off really closes the carburettor fully, and always have a way to stop the engine by hand.

1. RPM sensor

Fit a magnetic RPM sensor (hall sensor) on the engine fan or clutch, and connect it to the flight controller's frequency input. On the Motors tab:

  • Turn on RPM Sensor.
  • Set the Main Rotor Gear Ratio from the engine to the main rotor (for a two-stage gearbox see Gear Ratios), and the Tail Rotor Gear Ratio.
  • Main Motor Pole Count: 2 for one magnet. (The setting counts poles; one magnet gives one pulse per revolution, like one pole pair.)

2. Throttle servo

Plug the throttle servo into the ESC / Motor 1 output. On the Motors tab:

  1. Throttle Protocol: PWM. The default Update Frequency of 250 Hz suits most digital servos; use 50 Hz for analogue servos.

  2. Start with a safe, narrow range so the servo can't bind:

    Setting Start at Becomes
    Motor Off 1300 µs Carburettor fully closed -- engine cut
    Low Throttle 1500 µs Lowest usable throttle (0%)
    High Throttle 1700 µs Carburettor fully open (100%)

  3. Connect the flight battery. The servo goes to Motor Off. Adjust Motor Off in small steps until the barrel is fully closed without the servo straining. (If the servo moves the wrong way, swap the Motor Off and High Throttle values -- or reverse the servo.)

  4. Set Low Throttle about 100 µs above Motor Off.
  5. Use Throttle Override at 100% and adjust High Throttle until the barrel is fully open, without binding. Live Update applies the changes immediately.

Low Throttle is not idle

Set Low Throttle so the engine won't keep running there -- below a real idle. The idle itself is set with Idle Throttle on the Governor tab (or in your radio). This keeps the 0-100% range linear, which the governor needs.

3. Governor

On the Governor tab:

  • Governor Mode: NITRO.
  • Throttle Type: NORMAL is the usual choice for nitro.
  • Idle Throttle: a reliable idle, with the clutch not engaging.
  • Handover Throttle: above the point where the clutch fully engages -- often 40-50%. Spool up by hand below handover (throttle on a slider or your collective stick), and the governor takes over above it.

Set the Full Headspeed on the Profiles tab, then see Governor Setup to test, and Governor Tuning.