Need help in identifying the cause of my copter crash in Loiter mode

I recently encountered a crash with my 12S setup equipped with a 30-inch propulsion system and 100KV motors. The All-Up Weight (AUW) is approximately 18kg. The ESCs use Oneshot125 PWM, which is set in the Cube Orange Plus, using the AUX pins CH9-12 as Motor Outputs.

After completing the initial parameter setup through the Mission Planner, I performed several successful flights, after which conducted an autotune. Although the initial flights had little to no oscillations, the vibrations were relatively high, occasionally reaching the first red line (30m/s/s) on the Z axis in the Vibe window. The X and Y axes had lower vibrations, ranging between 10-20m/s/s. Despite the high vibrations, I proceeded with further flights in Loiter mode since all clippings were zero.

On a windier day, I flew an entire set of batteries successfully, even though the vibrations were higher this time, and the Y axis touched the red line occasionally.

However, during a manual flight in Loiter mode, while performing a pitch back maneuver, the copter lost yaw and started rotating until it hit the ground. It did not flip over. Unfortunately, I was unable to identify the exact cause of the crash. Here are some of my speculations:

  • The high vibrations could have been a contributing factor. The board is mounted at the CG directly, using the foam pads provided with the Pixhawk.
  • I disabled the internal compass since it was enclosed entirely. Instead, I used the compass in the GPS, which is a Here2.

I have attached the log file to this post for reference: Log file Drive Link

It would be of great help if someone could offer some insights into the possible causes of the crash.

P.S: The mode change to autotune in the end was when I accidentally hit the switch for it along with the disarm switch when it was already about to hit the ground. You can see how it lost yaw and started losing altitude, which was when I hit the disarm switch.

The vibration levels are too high. Loss of thrust on Motor 2. Classic signiture.

What’s the reason for using Oneshot125? Which ESC’s?

The ESCs are a new product made by a startup company. They recommended using Oneshot125 when I reported to them that the motors vibrate a lot in flight (signal by autopilot) but they don’t vibrate a bit on the bench, or when run through the motor test window. I personally haven’t seen a difference though, the motors still vibrate when the signal is given through autopilot in any flight mode.

Can vibrations lead to loss of thrust?

Nothing new about Oneshot125. Get yourself some BLHeli_32 ESC’s. The outputs are oscillating. If you ran Auto Tune (prematurely), and it looks like you did, it wasn’t good. Reduce the vibration levels, configure the Notch filter and try again.

I don’t think changing to Oneshot125 from PWM will solve anything. What Manufacturer told you that?

Yes, you’re right, the Oneshot125 did not help in any way.
Data from the BLHeliSuite:
BLHeli_S Rev 16.7
ESC Layout is I-H-05
Motor Timing is set to Medium.

So is it some issue with ESC? Do I have to replace with a different model ESCs?

As for reducing the vibration, with this hardware system I have not been able to do so mechanically. Would setting up the notch filtering effectively turn down all issues due to the vibrations?

No, but there are good reasons to do so. I would just set those to PWM. Or if there is Blujay firmware available for them flash that and use the Bdshot version of firmware for your flight controller.

No. It’s not a solution for bad mechanical vibration. But it needs to be configured anyway.