Betaflight failsafe

The receiver reports each channel as a pulse width in microseconds. Betaflight treats a pulse as valid only when it sits between the minimum and the maximum on the Failsafe tab. Both limits can be set from 750 to 2250 microseconds, in steps of 5. A typical radio sits near 1000 at one end and 2000 at the other, so the window is wider than the sticks on purpose: a slightly short or long pulse still counts as a link.

If the receiver stops sending, or sends a pulse outside that window, the flight controller treats the link as lost. Stage 1 holds the channels at their fallback values instead of following a dead stick. That is the short pause. It exists so a one-frame glitch does not disarm the quad or start a landing. The length of that pause is the stage 2 guard time.

The guard time is stored in tenths of a second and shown in seconds, from 0.1 to 20. A short guard time reaches stage 2 quickly, which is what most freestyle pilots want if the procedure is drop. A longer guard time gives the link more time to return, which matters more when stage 2 is a landing or a GPS Rescue that you do not want to start on a brief fade.

Set the window from a real receiver, not from a guess. With the radio on and bound, the Receiver tab shows the live channel values. The failsafe minimum should sit below the lowest stick or switch value you actually see, and the maximum should sit above the highest. If a switch already reaches 1000 and 2000, a window of about 885 to 2115 is a common starting point on many boards, but the number that matters is the one your receiver produces. Save, then power the radio off for a moment and confirm the craft enters failsafe instead of holding a full stick.

When the guard time runs out, Betaflight runs one of three procedures. The Failsafe tab lists them as land, drop and GPS Rescue. Land is procedure 0. Drop is procedure 1. GPS Rescue is procedure 2. The labels in FlySpark match those three Betaflight 4.5 choices.

Land tells the flight controller to level the craft and hold the landing throttle you set. The landing throttle is a pulse from 1000 to 2000 microseconds, in steps of 5. It is not a percentage. A value near the hover throttle descends. A value at the bottom of the range is close to idle and can drop the craft if it is too low to hold altitude. After the motors-off delay, the motors stop. That delay is 0 to 20 seconds, shown in tenths. Use it so the craft has time to reach the ground before the motors cut, and do not treat it as a guarantee of a soft landing.

Drop disarms. The motors stop and the craft falls. There is no levelling and no throttle hold. Pilots who fly close to people or over hard ground often still choose drop because a blind landing can travel, while a drop stays near the last position. The drop-if-low timer is separate: if the throttle has already been low for that long, Betaflight can drop even when the procedure is land. That timer runs from 0 to 30 seconds, in tenths. It is there so a landed craft does not keep the motors spinning for the whole landing delay after the link dies.

GPS Rescue tries to fly back toward home and then descend. It needs a GPS fix, enough satellites, and the rescue block filled in. Choosing the procedure does nothing useful if the GPS Rescue section is left at values the craft cannot fly. The same rescue settings are used when you flip the GPS Rescue mode on the Modes tab, so a switch test and a failsafe test are not two different tunes.

Some pilots put failsafe on a switch so they can test it without turning the radio off. The switch action has three choices. Stage 1 holds the fallback channels, the same as the start of a real signal loss. Kill stops the motors. Stage 2 runs the procedure immediately, which is the one to use when you want to see a landing or a GPS Rescue without waiting out the guard time.

A switch test is not a full test. Turning the radio off also removes the link the other way, and a switch only simulates the mode you mapped. After the switch works, do one short test with the radio powered down, props off, and confirm the flight controller announces the stage you expect. Then test with props on only at a height and place where a drop or a wrong landing throttle cannot hit anyone.

Map the switch on the Modes tab. Failsafe is one of the mode boxes the board reports. The range is the usual 900 to 2100 microsecond channel window, in steps of 25. The switch does not replace the pulse limits. A lost link still uses the guard time and the procedure even if you never assign the switch.

The return block is the same one described on the GPS and GPS Rescue page, and it sits on the Failsafe tab because the procedure and the mode share it. Altitude mode is the highest point so far, a fixed altitude, or the current altitude. Return altitude is 5 to 1000 metres. Extra climb is 0 to 100 metres. Climb rate is 0.5 to 25 metres per second. Return speed is 0 to 30 metres per second. Maximum pitch is 30 to 60 degrees. Minimum distance from home before rescue will start is 10 to 30 metres.

Descent starts at 10 to 500 metres from home. Descent rate is 0.3 to 5 metres per second. Minimum, hover and maximum throttle are each 1000 to 2000 microseconds, in steps of 5. Minimum satellites is 5 to 50. Sanity checks can be off, on, or failsafe only. Arming without a GPS fix is a separate switch, and leaving it on means the craft can arm when rescue would have nothing to fly back to.

Do not copy a rescue tune from another quad. Hover throttle depends on weight and prop size. A return speed that is fine for a light freestyle quad can be too fast for a cinewhoop and too slow for a long-range frame. Read the live GPS satellite count on the GPS tab before you trust the procedure, and read the receiver page if the link itself is the thing failing.

Below the procedure, the Failsafe tab shows a fallback value for each channel. Stage 1 uses those values. Roll, pitch and yaw should sit at centre so the craft does not roll hard during the guard time. Throttle should sit at a value you have chosen on purpose, not at whatever was last saved from a different model. Aux channels should sit where your modes are safe: arm off, turtle off, and any launch mode off.

If a fallback throttle is high, stage 1 climbs for the whole guard time. If a fallback roll is not centred, stage 1 flies sideways. Both are easy to miss because the procedure section looks more important. Set the fallbacks, save, and watch the receiver bars while you switch the radio off. The bars should jump to the fallback values, not to zero and not to the last stick position, once the link is actually gone.

Channel order follows the receiver map. If the map is wrong, the fallback you typed for throttle lands on yaw. Fix the map on the Receiver tab first, then set fallbacks. A change of receiver protocol can remap channels, so check the fallbacks again after you change a protocol or a radio model.

The Failsafe tab does not bind the radio. Binding and the protocol are on the Receiver tab. It does not set arming angles or the GPS Rescue mode range. Those are on the Modes tab. It does not calibrate the compass or set the GPS baud. Those are on the GPS page and the Ports tab. A rescue that never starts is often a port, a baud or a satellite count, not a wrong landing throttle.

INAV's failsafe is a different screen. INAV can land, drop or return to home, and the return-to-home altitudes live with the INAV navigation settings. Calling that GPS Rescue is wrong. If you fly INAV, open the INAV configurator and use its failsafe and navigation fields. The procedure names on that screen are the firmware's own names.

The Betaflight demo board in FlySpark is a simulated Betaflight 4.5. You can open the Failsafe tab and read every field without hardware. Saving to a real board needs a connection: USB or Bluetooth in Chrome or Edge, USB, Bluetooth or Wi-Fi in the Android app, and Bluetooth or Wi-Fi on iPhone. iPhone cannot see a flight controller over USB.