My copter with PIXHAWK was working great after finishing autotune for all 3 axis. I flew it several times with no problem. Today, I took off as normal in Alt Hold mode and it was very jittery and was erratic with the altitude too. I tried to land it but it came down rather suddenly and just flipped over.
I will attach the log to see if someone can help me understand what suddenly went wrong. MissionPlanner.log (500.1 KB)
From a quick look,
Your problem seems to be not enough power and/or being unbalanced.
Your throttle is pegged to the max but the copter is reluctantly climbing with motors 3 and 4 being pulsed to minimum for most of the flight.
Were you fighting a breeze?
As @bendead noted your battery is barely keeping up with such a large voltage drop and you haven’t set up current measuring so I can’t tell you any more there.
For further help you really need to give us more detail about your setup and the flight in question.