When Flight termination is activated, PX4 simultaneously turns off all controllers and sets all PWM outputs to their failsafe values.
Depending on what devices are connected, the PWM failsafe outputs can be used to:
- Deploy a parachute.
- Extend retractable landing gear.
- Move a PWM-connected gimbal to a safe orientation (or retract it) in order to protect the camera.
- Trigger an inflatable device like an airbag.
- Trigger an alarm.
There is no way to recover from flight termination. After triggering you should unplug the battery as soon as possible. You will need to reboot/power cycle the vehicle before it can be used again.
PX4 does not know what safety devices are attached - it just applies a predefined set of PWM values to its outputs.
Failsafe values are applied to all outputs on termination. There is no way to configure independent time-based (or other) triggering of the motors or specific safety devices.
This is not an independent Flight Termination System. If power is lost or if the autopilot crashes completely, the failsafe devices will not be triggered.
Any safety device(s) (e.g. a parachute) that can be triggered by changing a PWM value can be used, and may be connected to any free PWM port (both MAIN and AUX).
If you're using Pixhawk-series board you will have to separately power the servo rail (i.e. from a 5V BEC, which is often also available from your ESC).
The Failure Detector can also (optionally) be configured to trigger flight termination if the vehicle flips (exceeds a certain attitude) or if failure is detected by an external automatic trigger system (ATS):
- Enable the failure detector during flight by setting CBRK_FLIGHTTERM=0.
- Safety > Failure Detector > Attitude Trigger explains how to configure the attitude limits that trigger Flight termination.
During takeoff excessive attitutes will trigger lockdown (kill motors, but not launch parachute) rather than flight termination. This is always enabled, irrespective of the value of
- Safety > External Automatic Trigger System (ATS) explains how to configure an external trigger system.
For each MAIN output to which a safety device is attached, where "n" is the PWM port number, set:
For each AUX output to which a safety device is attached, where "n" is the PWM port number, set:
Finally, set the
PWM_MAIN_FAILn PWM values for any motors.
The diagram below shows the logical flow around flight termination.