Governor¶

The governor holds the headspeed constant -- whatever the collective, the manoeuvre or the battery voltage. It also spools the rotor up gently, recovers quickly if you flick throttle hold by mistake, bails out of autorotations, and copes safely with a lost RPM signal.

The Rotorflight governor works with electric motors and with nitro and petrol engines. This page explains how it works; Governor Setup walks through setting it up.

Settings are split between the Governor tab (global) and the Profiles tab (per profile -- headspeed and gains).

Governor modes¶

Mode	What it does	Needs RPM
OFF	No governor: the throttle channel goes straight to the ESC.	No
LIMIT	No governor, but the idle, minimum and maximum throttle limits are applied.	No
DIRECT	Throttle follows your input, but with slow spoolup, fast recovery and autorotation bailout. For an ESC with its own governor, or a throttle curve in the radio.	No
ELECTRIC	The full governor, tuned for electric motors.	Yes
NITRO	The full governor, tuned for nitro and petrol engines.	Yes

ELECTRIC and NITRO need a fast RPM signal -- see RPM Measurement. Without one, the flight controller won't arm (GOVERNOR flag).

The throttle channel¶

The throttle channel's range is shown as 0-100%. Below 0% is the stop range: the motor is off, and that's where the throttle must be to arm (your throttle hold value).

 ┌ stop ┐┌──────────────────────── active ────────────────────────────┐
         0%                                                        100%
 ├┄┄┄┄┄┄┄┾━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┽┄┄┄┄┄┄┄┤

Handover¶

The handover throttle divides the range in two. Below it is idle: the throttle goes straight to the motor. Above it, the governor takes over.

        ┌───── idle ─────┬────────── governor enabled ───────────────────┐
        0%              25%                                          100%
 ├┄┄┄┄┄┄┾━━━━━━━━━━━━━━━━┿━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┽┄┄┄┄┄┄┄┤

The motor must be able to start below the handover point. On a nitro helicopter, the clutch must engage below it.

Target headspeed¶

Above handover, the target headspeed is the profile's Full Headspeed × the throttle input. With a full headspeed of 2500 rpm, 90% throttle aims for 2250 rpm and 100% for 2500.

Throttle types¶

How you use the throttle channel depends on the Throttle Type:

NORMALSWITCHFUNCTION

The throttle channel drives the motor directly until the target headspeed is reached; then the governor takes over until the throttle goes back below handover. Works with throttle on a switch or a throttle curve on the stick (set the flat part of the curve to your headspeed percentage).

The ramp-up follows your input, limited by the spoolup time.

Below handover the channel drives the motor directly (idle). Above handover it selects the headspeed. Use a switch that jumps between positions -- for example 10% idle, then 80% and 90% for two headspeeds:

              10%                                   HS 80%  HS 90%
        0%     ▼        25%                             ▼       ▼    100%
 ├┄┄┄┄┄┄┾━━━━━━━━━━━━━━━━┿━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┽┄┄┄┄┄┄┄┤

Not for throttle-on-stick. ELECTRIC and NITRO only.

The throttle position picks a governor function:

 ┌ OFF ┐ ┌─────── IDLE ───────┬─────── AUTO ───────┬─────── RUN ────────┐
         0%                  33%                  66%                 100%
 ├┄┄┄┄┄┄┄┾━━━━━━━━━━━━━━━━━━━━┿━━━━━━━━━━━━━━━━━━━━┿━━━━━━━━━━━━━━━━━━━━┽┄┄┄┄┄┄┄┤

Function	Throttle output
OFF	Motor stopped.
IDLE	The Idle Throttle setting.
AUTO	The Auto Throttle setting -- autorotation practice.
RUN	Governed, at full headspeed.

Ideal for ExpressLRS, whose low-resolution switch channels can't carry a precise throttle value. A typical setup: a throttle-cut switch for OFF, and a 3-position switch for IDLE / AUTO / RUN.

ELRS wide channels

NORMAL and SWITCH need a full-resolution throttle channel. ExpressLRS's wide switch channels aren't precise enough -- use FUNCTION, or put throttle on a full-resolution channel.

States¶

The governor moves between states on its own, depending on the throttle input and what the motor is doing. The current state is sent to your radio as a telemetry sensor.

State	When	What happens
OFF	Throttle below 0%	Motor stopped.
IDLE	Throttle below handover	Throttle passed to the motor, limited by the startup ramp. Expected on the ground.
SPOOLUP	Throttle raised above handover	Ramps up to the target headspeed at the spoolup rate.
ACTIVE	Target headspeed reached	The governor holds the headspeed, with precompensation for collective, cyclic and yaw. Target changes follow the tracking rate.
THROTTLE HOLD	Throttle cut while ACTIVE	Spooling down. If throttle returns within the Throttle Hold Timeout, it recovers quickly instead of a slow spoolup.
RECOVERY	Coming back from hold or fallback	Fast ramp to the target, at the recovery rate -- the helicopter is probably in the air.
AUTOROTATION	Throttle dropped into the auto range while ACTIVE	Motor at idle or auto throttle; raising the throttle triggers a bailout.
BAILOUT	Throttle raised during autorotation	Fast spoolup at the recovery rate.
FALLBACK	RPM signal lost or unreliable	Throttle held at an estimated value, reduced by the Fallback Drop so you notice -- land.
BYPASS	GOVERNOR BYPASS mode switch on	All governor functions off; throttle from the bypass curve.

Autorotation bailout¶

To practise autorotations with a fast bailout:

Set an Autorotation Timeout on the Governor tab (0 disables bailout).
Set Auto Throttle below the handover throttle.

Autorotation is detected when, while governed, the throttle drops into the range between Auto Throttle and handover. Raise it above handover to bail out. Dropping below Auto Throttle -- e.g. into idle after landing -- cancels the autorotation, and the next spoolup is a normal, slow one.

        ┌ idle ─┬─ auto ─┬────────── governor enabled ───────────────────┐
        0%     12%      25%                                          100%
 ├┄┄┄┄┄┄┾━━━━━━━┷━━━━━━━━┿━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┽┄┄┄┄┄┄┄┤

Idle throttle in the flight controller¶

If one radio model flies several helicopters, the idle level can live in the flight controller instead: Idle Throttle sets a minimum motor output whenever the motor is running below handover. The radio can still send a higher idle.

Mode switches¶

Mode
GOVERNOR BYPASS	Turns the governor off entirely and uses the collective-based bypass throttle curve. No ramps, no safeguards. A get-out for a failed RPM signal.
GOVERNOR FALLBACK	Simulates a lost RPM signal, to test what fallback feels like.
GOVERNOR SUSPEND	Suspends the governor's PID, leaving only precompensation. For testing.

Output throttle range¶

The governor's 0-100% output maps onto the Motors tab's throttle range:

Low Throttle is 0%. On electric, the motor shouldn't run there, but should start just above it.
High Throttle is 100% -- full throttle.
Motor Off is below Low Throttle, where the motor is guaranteed to stop. It's also what lets the ESC arm.

Every change within the range must change the motor's power -- no deadbands. The motor must start below 5% and reach full power at 100%. Calibrate the ESC's throttle range to match.