2023-02-19 - RCA for Frosted Flakes Crash Feb 19th

📋Incident overview

🔮 Executive summary

• Crash Photos

• Crash Logs

  • These are linked in Discord by Anni currently

  • Flight Test Thread

• These need to be parsed

• During this debrief we are reviewing the crash footage & Ardupilot telemetry logs

  • "batteries sag to <3v per cell during transition"

  • Had trouble maintaining fixed wing attitude

    • Looking at logs is that the elevator input makes almost no change in attitude

      • Could’ve been caused by airspeed being too low

  • Roll input is weak as well

    • Possibly all of our control surfaces are weak due to low airspeed ?

      • As we get faster servos require more power to work

      • Consider making controls out of something else, maybe a different

  • From logs it started falling as soon as the quad motors shutoff

    • Prime theory is we weren't going fast enough when quad motors shutoff

    • yaw is a bit weird but possibly not the issue

    • We should check pixhawk parameters and that would give us more information

• There was only one servo on the elevator

  • Two servos total were ripped off the drone

  • Both rudders were ripped

  • Confirmed from photos, elevator one exists, both rudder ones were ripped off.

    • If the control input was mapped in reverse and the servo was reversed the acro mode on the ground is correct, but when the autopilot does something it is reversed.

      • quad mode it worked, but when ardupilot controlled it, it was the other way around

      • We can check this, but later

        • Anni has never had to reverse a servo in ardupilot

• There was some roll and battery sag that could’ve caused stuff

• This seems like the most likely theory from the logs

• We can’t really confirm because the servo was ripped off, but hopefully we have pictures of the photos before it was damaged

• Damage was 2 motors, 2 props, entire airframe, at least one wing

  • Other electronics are okay

  • One battery is GGed (puffed out), other is probably bad but needs to be replaced anyways

    • these were old batteries anyways

    • We have more motors coming in, but we are out for now

    • Both have been clearly sharpie labelled

• Design airframe to protect critical components in the future

  • We need some way to protect the motor

  • This is more about protecting the motor than the prop, Mech to reassess

• We will need to retest all electronics following this even the ones that aren't visually destroyed.

• We weren't able to successfully transition back to quad during the crash

  • From logs it seems like it was trying to pull out of nose dive before transitioning to quad

  • It cant transition to quad when at such a steep angle - it may want to turn all on at once

    • Possibly the aircraft was fully inverted

    • Data cuts off at 40m altitiude.

      • We crashed above where we took off, but no way it was 40 meters

      • We need to take photos as we unplug and disassemble the cabin to see if the Pixhawk was unplugged

        • We should check things sooner rather than later to assess if we need to reorder stuff.

• Someone needs to take this mess of notes and properly fill out this RCA lmao

⏱ Incident timeline

Describe (approximate) timelines, cross-correlate with telemetry/video recordings/etc if any.

Pilot inputs as perceived by pilot on sortie 3:

• arm

• took off in QLoiter

• switched to FBWA

• switched to QLoiter

• switched to FBWA

• spammed the button to switch to QLoiter

⛑ Postmortem report

✅ Recommendations for future