Arming & Safety

A helicopter rotor is dangerous. Rotorflight has several layers of protection between "battery plugged in" and "rotor spinning" -- this page explains them, and how to read what the flight controller is telling you.

Blades off

Remove the main and tail blades for any setup work that can spin the motor: motor or mixer override, governor and ESC setup, arming tests.

Arming is not throttle hold

You need two separate switches on your radio:

	Arm switch	Throttle hold
Lives in	The flight controller (the ARM mode)	The radio (sets the throttle channel to its minimum)
What it does	Enables the flight controller's outputs to the motor, and starts the stabilisation	Keeps the motor stopped, or stops it in flight for an autorotation
When you use it	Once before take-off, once after landing	Whenever you need the motor to stop -- including in flight
In flight	Never switch it off -- disarming stops the motor and the stabilisation, and the helicopter will crash	Safe to use; the governor can bail out of an autorotation

Put the arm switch where you can't knock it by accident. Put throttle hold where you can reach it instantly.

Setting up the arm switch

1. On the radio, put the arm switch on a spare channel so it sends about 1000 µs when disarmed and 2000 µs when armed.

   ELRS / CRSF receivers

   Use AUX1 (channel 5) for the arm switch. ExpressLRS sends AUX1 at full rate and uses it to know when the model is armed. See ExpressLRS switch configs.

2. On the Modes tab, add a range for ARM on that channel, covering the upper end of its travel.

3. Save, then flip the switch: the marker should move into the range and the ARM mode lights up.

The arming sequence

The flight controller arms only when every check passes. The usual order at the field:

1. Throttle hold on, arm switch off.
2. Plug in the battery and keep the helicopter still and level while the gyro calibrates.
3. Wait for the ready wiggle (below) -- the flight controller is happy to arm.
4. Arm.
5. Release throttle hold to spool up.

After landing: throttle hold on, wait for the rotor to stop, disarm, unplug.

Swashplate wiggle

Before the first arming after power-on, the flight controller "talks" by moving the swashplate:

Wiggle	Meaning
One short wiggle when arming becomes possible	Ready. Nothing is preventing arming.
Short collective bounce every 3 s while the arm switch is on	Can't arm yet -- something temporary, such as throttle not at zero, the helicopter not level, failsafe, or the RX not connected. Fix it and toggle the arm switch.
Long collective bounce every 5 s while the arm switch is on	Configuration error -- something that needs fixing on the bench: no gyro, CPU load too high, governor or RPM filter without an RPM signal, accelerometer not calibrated, no motor protocol, or reboot required.
One brief movement on arming	Armed (off by default).

Ready to arm

Can't arm yet -- arm switch on

The wiggles only happen before the first arming of a flight, never in flight. They're configured from the CLI:

Setting	Default
wiggle_enable_ready	ON	Ready wiggle
wiggle_enable_error	ON	Short error bounce
wiggle_enable_fatal	ON	Long error bounce
wiggle_enable_armed	OFF	Wiggle on arming
wiggle_strength	50	How far the swashplate moves (0-100)
wiggle_frequency	10	How fast it moves (2-50)

Arming disable flags

When the flight controller refuses to arm, the reason is shown as one or more arming disable flags. You can read them:

• On the Status tab of the Configurator.
• On the radio, in the Rotorflight Lua suite.
• In the CLI, with the status command.

Flag	Meaning	What to do
NO_GYRO	No gyro detected.	Check the board selection; the gyro may be faulty.
FAILSAFE	Failsafe is active.	Check the receiver link.
RX_FAILSAFE	No valid signal from the receiver.	Check wiring, protocol and UART on the Receiver tab, and that the radio is bound.
BAD_RX_RECOVERY	The receiver has just recovered from failsafe while the arm switch was on.	Toggle the arm switch.
BOXFAILSAFE	The FAILSAFE mode switch is on.	Turn it off.
GOVERNOR	The governor is enabled but has no usable RPM signal.	Set up RPM measurement.
RPM_SIGNAL	A required RPM signal is missing.	Check the motor pole count and the RPM source on the Motors tab.
THROTTLE	Throttle is not at zero.	Turn throttle hold on, or lower the throttle.
ANGLE	The helicopter is not level.	Level it (within 25° by default).
BOOT_GRACE_TIME	Too soon after power-on.	Wait a moment and arm again.
NOPREARM	A PREARM mode is set up but not switched on.	Switch PREARM on before arming.
LOAD	CPU load is too high.	Lower the PID loop frequency on the Configuration tab, or turn off features.
CALIBRATING	Sensor calibration is still running.	Keep the helicopter still until it finishes.
CLI	The CLI is open.	Leave the CLI.
CMS_MENU	An on-screen menu is open.	Close it.
BST	A Black Sheep Telemetry device is preventing arming.	See the device's manual.
MSP	The Configurator is connected.	Expected while connected -- see below.
PARALYZE	PARALYZE mode was triggered.	Power cycle the flight controller.
GPS	A GPS fix is required but missing.	Wait for a fix.
RESC	The RESCUE mode switch is on.	Switch rescue off.
RPMFILTER	RPM filtering is enabled but an RPM signal is missing.	Set up RPM measurement, or turn off the RPM filter.
REBOOT_REQ	Settings were changed that need a reboot.	Reboot the flight controller.
DSHOT_BITBANG	DShot bitbang failed.	Check the board's timers and DMA, or set dshot_bitbang = OFF.
ACC_CALIB	The accelerometer needs calibrating.	Calibrate it on the Setup tab, or turn off the features that use it.
MOTOR_PROTO	No motor protocol is selected.	Select the ESC protocol on the Motors tab.
OVERRIDE	Servo, motor or mixer override is on.	Turn off all overrides.
ARM_SWITCH	The arm switch is on but something else is blocking arming, or it was on at power-up.	Fix the other flags and toggle the arm switch.

Arming with the Configurator connected

The MSP flag stops the helicopter arming while the Configurator is connected. For bench tests you can lift it with Enable Arming on the Status tab. Blades off -- with arming enabled, releasing throttle hold spools the motor up.

Failsafe

If the receiver loses the radio link, the flight controller holds the controls for a short time, then goes into failsafe. Set up what happens -- and test it, blades off, by switching the radio off -- on the Failsafe tab. Your receiver must be set to send no pulses (or the flight controller's own failsafe values) on signal loss, not to hold the last throttle position.