Add vertical emergency braking in auto mode #18277
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Currently only for the Z axis. If the current downward velocity is more than twice the maximum allowed value, the emergency braking mode is activated. In this mode, a higher vertical acceleration and jerk is used until the vehicle stops moving.
When engaging auto mode at high vertical speed, we don't want to cut the velocity trajectory setpoint in order to create a smooth deceleration.
bkueng
approved these changes
Sep 23, 2021
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Describe problem solved by this pull request
If the drone is sinking really fast (i.e: well above usual maximum descent speed) and if the user switches to an auto mode to recover (RTL or other), the trajectory generator will generate a smooth (from design parameters) that usually creates a too long braking distance. Furthermore, the setpoints are clipped by the velocity controller, creating a hard stop followed by a controlled descent (that looks like an overshoot).
Describe your solution
If the drone is falling at a speed above twice the maximum downward speed, the trajectory generator enters an "emergency braking mode" that sets higher acceleration and jerk parameters (9.81m/s2 and 9.81m/s3) until the vertical velocity trajectory reaches 0m/s. After this, it goes back to normal and uses the usual parameters to continue the mission.
Test data / coverage
SITL:
https://logs.px4.io/plot_app?log=c47a8da3-6bc5-4d9f-88d6-3643465b0c42
And real flight tests. We use that on our vehicles for ~3 months