[TALLGUY64]

hey all,

Just finished building a s500 frame, flying on 4s with 30amp esc with beheli driving 3506 650 kv motors spinning 1245 props all controlled with a revolution using an external gps mag combo. Did all the calibration supper meticulous. Super low mag errors at all angles, never higher then 2% even when standing next to my truck. in the field seemed to be at or below 1%. So i armed bliped the throttle, no roll over, then took off, hovered for a min made sure i could maintain control, switched into autocal, finished and landed and saved the settings, switched over to the new settings was getting dark so kinda hard to notice any slight oscillations, wasn't super happy didn't feel right, but pushed on till.... it crashed. It was the oddest crash i have had yet. I have a small 250 chinese zmr and have done all kinds of bad with that  . I have a feeling it is due to the PID settings but i figured i would ask.

The crash, As i was hovering, not moving it literately did a 180 flip/roll and went straight into the ground. It was about 6 to 8 feet of the ground, no wind just manual hovering in attitude. It happened so fast that i didn't have time to notice which axis it happened in. There was no major oscillations before it flipped, when it did flip it did it faster then i have been doing some flips with my 250  . 

Like i said i didn't like the feel of it, it felt really twitchy. I have over done it with my 250 and i have had some bad oscillations and then a crash because i got out of control. but never had it feel okish then just flip and straight into the ground.i am guessing i should start off from scratch and do manual tuning.

Anyone had this happen or your thoughts? Thanks!

[TheOtherCliff]

Many possibilities.  The first one that comes to mind is vibration.  Past a certain level it makes the gyros go crazy.  Balance your props.  Log a flight and/or look at the accel scope.  1g is about 10m/s/s.  A normal hover should see about -1g vertically and 0g's horizontally.  If you see vibration that adds more than a few g's to this, it is an issue, and above some level the gyros do go crazy.  The g sensor has a limit and clips above some level, like 8g's or such...  I forget.  Also, when the g sensor starts to clip (past max value) then the g sensor itself can make it flip (but not flip quickly) in self leveling modes like Attitude mode.

Bad connection to an ESC could cause it.

Did it drop when it happened like one motor stopped working or flip first if you could tell?

Did all motors stop at about the same time?

Crash damage of many kinds... FC power lost momentarily.  Cracked FC or BEC.

[TALLGUY64]

I took a lot of time balancing props by sanding them like I used to on my rc plane. At low rpm one at a time I checked for vibration before I flew they felt good. I definitely need to record my next flight, didn't even think about it.

From what I could tell all the motors were working when it drove into the ground, right after I ran the motors to check to make sure nothing was damaged and it fired right up but I was done and it was really getting to dark.

Best way I can describe the flip was as if I yanked the stick hard let up when the was upside down and didn't let of the throttle. Kinda like doing a split s with out throttling down.

From what I can tell no permanent damage besides two broken props.

[TALLGUY64]

I'm still going to look the pid's, anyone know of some good pid's I think I need to drop mine because of the power of the motors.

[TheOtherCliff]

A bad AutoTune could do it, but generally a bad AutoTune won't fly at all.  I wouldn't expect it to fly, then flip.

If you post your settings UAV file I can look at the AutoTune results and PIDs.