Greetings... a bit long, but please read on :

Hexa, APM 2.5, 2.8.1    A few weeks of trouble free flying. Then while in stab/simple mode,  bearing suddenly starts to drift about 60 degrees,  but only when I yaw left or right. When the nose is in the GPS locked take off direction (pardon my terminology) it holds true. As soon as the nose is turned left or right, it gradually starts to shift bearing in that direction, (as if it is shifting to just stable mode). It was suggested that I check for wiring interference. Everything good as far as I can see, but problem persisted.

Then it was suggested I upgrade to 2.9.1, so I did. With all the required things done for 2.9.1, including foam under the APM,  checked PIDs, everything calibrated... I also insured again that all the wires inside were neat & tidy, and took it for a test flight. Again, stable until I turned the nose left about 90 degrees - the bearing drifted in that direction. So when I tried to move forward, it would pitch to the left about 60 degrees. When I tried to bring it back to me, it pitched right about 60 degrees. It was flyable, but I had to adjust. I landed, back on the bench.

The next day, the last 2 flights: Made sure switches all good on the Tx. I take off, hover about 15ft in the air. Suddenly it starts to move to my left without me touching anything. As I try to counter it, the roll stick does less and less, 'till the stick is as far to the right as it will go! The copter  just keeps pitching way off to the left... no control. It crashed, but no apparent damage. I take it in, check it all through, recalibrate everything, & try again. This time, I hover it right in front of me at about 6 feet off the ground. Stable for 30 seconds, then it starts to move off to the right. I took my hand off the controls for a second, and it takes off towards 3 o'clock, pitched right over. Controls maxed out to counter it, I had no control. Crashed again.

It's on the bench. Logs attached, 3 more to follow. (no wireless telem, USB to APM).

Any thoughts?  Thanks...


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Here are 3 more Logs:



Hi Mick, 

we need Randy or other logs guru to review these, I know you logged a lot of nice flights on that Hexa and this sudden change needs to be explained.   

@ Drone Savant, hahaha that is funny!  :) 

For the record I sold Mick this copter, and if anyone points it out to be a hardware issue I will issue an RMA. We just need to understand what is going on as nothing has changed, the cables are clean and not causing any more interference as before when it was working fine.   

Thanks guys, need your help! 


It sounds to me, you might get some pronounced leans, due to strong vibrations.

Haven’t checked your logs yet.

Vibrations beyond the foam I put in for the APM ?

What value is INS_MPU6K_FILTER? Did you try 20?

Tnx for the reply... I left all default values from firmware. Didn't change any params, but I can give it a try if that would help. What will that do?

It reads the sensors at different frequencies (value of the INS_MPU6K_FILTER). I think 50Hz is default.

So with INS_MPU6K_FILTER = 20, the read frequency is 20Hz.

So if your vibrations are a multiple of the read frequency, you might get an aliasing effect which can lead to leans.  

I have INS_MPU6K_FILTER = 10.

I'm still learning how to interpret the logs, but I'll give it a go.  Here are my observations from looking at log #85:

Your GPS altitude and your baro altitude generally show movements in the same direction, but do show some differences.  Your mix altitude shows pretty much the opposite of the other two.  On my quad, these three values track reasonably closely with each other, so this might be a problem.

The values reported for ClimbRate seem completely unreasonable.  Your quad wasn't falling at 140+ m/s was it?

The pitch values show an increasing trend during your flight until they reach nearly 45°, and your pitch input correlates with this. However, your position track is nearly stationary.  After you shut the props down, the pitch (and to a lesser extent, the roll) gradually decays to zero.  This is highly suspicious to me.  If I had to guess, it looks like the copter thinks it is leaning over, just like "the leans" as described in the link that DS posted above, and you are having to match your input to what it thinks its orientation is so that it doesn't "correct" and and actually tip over.

Your AHRS_GPS_GAIN is 0 but AHRS_GPS_USE is 1. The mission planner says the gain parameter controls how much the GPS is used to correct attitude.  If you're using it but have a gain of zero, and expecting attitude corrections, then that might be a problem.  I'm not familiar enough with the settings/code to say for sure.

Your INAV_ACORR_ parameters are much different than mine.  I don't know what (if anything) these are used for.

And that's as much as I can make sense of right now.

Thanks Dan, I will go over this again.

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