Jan 22, 2023 - Cornflakes

1 Incident overview | 2 Executive summary | 3 Incident timeline | 4 Postmortem report | 5 Recommendations for future

Incident overview

Postmortem owner	@Dhruv Upadhyay @Sahil Kale
Airframe	Cornflakes
Related incidents	-
Incident date	Jan 22, 2023
Approx. Damage Costs	$70 + cost of motor
Report Date	Jan 22

Executive summary

Cornflakes, while flying in VTOL mode, suffered an ESC failure on Motor 2 (Front Right). The ESC failure caused the drone to no longer fly in a stable manner. Due to the imbalanced roll experienced by the aircraft, the drone was very unstable. PIC opted to roll the A/C left to level the airframe before disarming the motor to prevent a dangerous situation from developing that harmed people or property.

Incident timeline

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

T-5 min before takeoff

Motor 2 is observed to have not spun when armed. After wiggling the ESC, the motor was successful in moving. The problem was clearly identifiable, however, due to a similar issue on cornflakes being observed before and running the motor on the ground for a long period at a raised throttle without issues, the decision was jointly made to continue flying.

T+15 seconds after takeoff

Motor 2 fails briefly. The pilot did not observe the first instance of the motor failure (they observed shaking but due to the orientation of the aircraft the motor failure was not directly seen)

T+30 Seconds after takeoff

Motor 2 fails permanently. The pilot assessed the following options:
- Lowering motor throttle
- Disarming the aircraft
The pilot opted to continue to the second option due to the risk of the aircraft rolling over and flipping. The aircraft was also unstable and may have drifted into people or property.
The pilot commanded roll left to the maximum possible extent to make the aircraft level to reduce potential airframe damage before ultimately disarming the motor from an altitude of roughly 10 meters.

In Bay

The ESC was observed in the bay and the following wire photo:

Postmortem report

Instructions	Report

Instructions

Report

Leadup

List the sequence of events that led to the incident.

ESC’s arrived much later than expected
Soldering was very rushed
Soldering was not well checked

Fault

Describe what didn't work as expected. If available, include relevant data visualizations.

DSHOT wires were not well soldered and were stressed. It is theorized that due to the poor soldering of the signal wire, a fray contacted the ground wire while under flight, causing a loss of command to the ESC’s

Detection

Report when the team detected the incident and how they knew it was happening. Describe how the team could've improved time to detection.

See above timeline

Response

Report who responded to the incident and describe what they did at what times. Include any delays or obstacles to responding.

Flight test team secured the aircraft right after flight. The drone was already disarmed and the batteries were disconnected.

Recovery

Report how the user impact was mitigated and when the incident was deemed resolved. Describe how the team could've improved time to mitigation.

Nil

Five whys root cause identification

Run a 5-whys analysis to understand the true causes of the incident.

Electing to continue flight testing on tight timeline
Failing to check over harnessing
Not having spare ESC’s available on flight line

It is theorized that due to the poor soldering of the signal wire on the ESC, frays of the signal wire contacted ground, preventing the flight controller from commanding the ESC, causing intermittent ESC failure.

Related records

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-

Lessons learned

Describe what you learned, what went well, and how you can improve.

Soldering to flight-control components should be verified by another individual with a signoff.

Giving a good once over before we fly is critical

Strain relief of connectors is important

An issue found post-flight is that another ESC’s ground wire broke off due to a cold solder joint, as well as poor strain relieving on signal wires. This caused the ground wire to come off during post flight inspection

Recommendations for future

Actionable Recommendation	Reasoning

Actionable Recommendation	Reasoning
Strain relief cornflakes V2	See lessons learned
Re-solder all ESC’s and verify the integrity of wires	2 of the 4 cornflakes ESC’s are inop due to the poor soldering issues