Copter crashes after short time in Loiter mode

Have a Pixhawk controlling a hexacopter built on a Tarot 680PRO frame. Also have the 3DR GPS/Compass module oriented and calibrated. Pixhawk is running ArduCopter 3.2.1. Radio is an FrSky Taranis with X8R Receiver.

After taking off in stabilize and then switching into AltHold then Loiter, the copter will be stable. All of a sudden it will go veer right and crash to the ground.

From reading other posts I thought this may have been from having the maximum loiter velocity set too high so I decreased it. I also re-ran the compass calibration. The next test flight showed that this was not the problem as the same thing happened again. On the second flight I also noticed that the copter twitched a few times right before it completely lost it’s stability and crashed.

I am at the point where I have no idea what is causing this, any help would be greatly appreciated.

From the logs it looks like the left side of the hex is heavier than the right. Then motor 4 goes to max and motor 3 goes to min causing it to lean right and forward.

You should switch to Alt Hold or Stabilize to see if stops leaning in that direction.


Hi !
That was a near miss :slight_smile:
In the diydrones someone mentioned its nose heavy !
I checked the motor numbers and then realized i did a complete wrong assesment of the COG / COT for this SPider frame.
I corrected that and the motor output is much more even now !

The Yaw “pumping” stayed…

Then i did a thorough retuning and also stepped up the Yaw P a LOT.

Now it looks fine and razor sharp (PID’s close to Mission Planner limits or over).

In the logs there is a Yaw sinus-like variation (Yaw curves around steady desired Yaw) but its a fraction of a degree and not visible, i hope that this is normal…