PX4 can be configured to trigger a parachute connected to a free PWM output during flight termination.
This topic provides the specific example of how to set up a parachute, using a spring-loaded launcher from Fruity Chutes (opens new window).
PX4 does not know that it is launching a parachute; during flight termination it just turns off all controllers and sets all PWM outputs to their failsafe values. You can therefore use this feature to activate multiple complementary safety devices connected to different outputs. For more information see Flight Termination Configuration.
# Using Parachutes
Below are a few considerations when using parachutes:
- A parachute does not guarantee that the vehicle will not be destroyed or cause harm! You must always fly with safety in mind.
- Parachutes require careful usage to be effective. For example, they must be folded correctly.
- Parachutes have a minimum effective altitude.
- A parachute may trigger while the vehicle is upside down. This will increase the time required to slow, and may result in the drone collapsing the parachute.
- The parachute will only deploy if the flight controller is powered and PX4 is running properly (unless it is triggered independently of PX4). It will not deploy if something causes the flight stack to crash.
# Parachute Setup
Flight termination (and hence parachute deployment) may be triggered by safety checks such as RC Loss, geofence violation, and so on, from attitude triggers and other failure detector checks, or by a command from a ground station. During flight termination PX4 sets PWM outputs to their "failsafe" values (failsafe values turn off motors, but may be used to turn on/trigger the parachute.
Parachute setup therefore involves:
- Connecting the parachute to unused outputs and setting their failsafe values to levels that will trigger the parachute (using appropriate parameters).
- Configuring flight termination as the appropriate action for those safety and failure cases where the parachute should be deployed.
The setup below explains how you might configure a quad multicopter with motors on MAIN 1-4 and a parachute on MAIN PWM port 7. The PWM values mentioned are for the Fruity Chutes parachute we tested.
For the first test, try on the bench, without the props and with an unloaded parachute device!
- Connect the parachute to the IO port (MAIN), channel 7 (starting from 1).
- Power the servo rail - i.e. connect a 5V BEC to the servo rail.
Enable flight termination:
Set Safety action to Flight termination for checks where you want the parachute to trigger
You can also configure an external ATS for failure detection.
- Set PWM_MAIN_DIS7 to PWM value for parachute "OFF" position (usually between 700 and 1000ms)
- Set PWM_MAIN_FAIL7 to PWM value for parachute "ON" position (usually between 1800 and 2200ms)
- Set PWM_MAIN_FAILn, where n is 1 - 4, to 900ms such that the motors directly go to disarmed values.
There is no way to recover from a Termination state! Reboot/power cycle the vehicle before your next test.
# Parachute Testing
The parachute will trigger during flight termination.
The easiest way to test a (real) parachute is to enable the failure detector attitude trigger and tip the vehicle over.
You can also simulate a parachute/flight termination in Gazebo: Development > Simulation > Gazebo > Simulated Parachute/Flight Termination.