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Yaw Instability and Crash in Loiter Mode – High Vibrations & Motor Imbalance Issues

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I am troubleshooting an issue that led to a crash while in Loiter mode. The drone in question is a heavier drone (~6-7 kg).

Before this test, we had flown the same drone successfully at 100m altitude, traveling 150-200m forward without any issues. As we were testing the impact of setting:

  • LOIT_SPEED = 3500 cm/s (35 m/s)
  • LOIT_ANG_MAX = 10°

Later during the next flight after changing the battery and re-flying, when we were specifically testing the impact of setting:

  • LOIT_SPEED = 3500 cm/s (35 m/s)
  • LOIT_ANG_MAX = 5°

We observed a motor failure when reversing yaw direction.

Critical Issue Observed:

  • When the pilot yaws the drone anticlockwise and then applies a small clockwise yaw command,
    Motor (C4) suddenly loses power, causing the drone to fall.

This can be seen in log using ATT>YAW and RCOU>C1, C2, C3, C4 and RCIN>C2
Additionally you can also plot the GPS>ALT to see when the altitude drops.


Observed Logs & Parameter Settings:

1. Yaw Instability (ATT Log)

2. High Vibrations (VIBE Log)

3. Motor Output Imbalance (RCOU Log)

4. Pilot Command for YAW (RCIN Log)


Current Parameter Settings:

Yaw PID Tuning (ATC_RAT_YAW)

Parameter Current Value Default Value
ATC_RAT_YAW_P 0.462 0.18
ATC_RAT_YAW_I 0.0462 0.018
ATC_RAT_YAW_D 0.0024 0

Other setting for YAW can be seen using the log.

Loiter Mode Parameters

Parameter Current Value Default Value
LOIT_ACC_MAX 300 cm/s² 500 cm/s²
LOIT_ANG_MAX N/A
LOIT_SPEED 3500 cm/s 1250 cm/s

Acceleration and Jerk Limits

Parameter Current Value Default Value
ATC_ACCEL_Y_MAX 6500 cdeg/s² 27000 cdeg/s²

Request for Help:

  • How should I further refine my Yaw PID tuning?
  • Could my ESC/motor combination be causing desync in yaw transitions?
  • Would increasing ATC_ACCEL_Y_MAX significantly improve yaw response?
  • Are there any known firmware issues or flight controller settings that could cause this behavior?

I have attached log files with parameter settings for reference. Any recommendations would be greatly appreciated!

LINK - 2025-01-17 14-41-53 (1).bin - Google Drive

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