Hello DIY Drones community,

I'm seeking some assistance trying to figure out the source of wobbliness on my Hexacopter.  I've attached the log here.  What happens is the drone will take off and it seems relatively stable.  I can generally make gentle pitch and roll commands and it responds as expected.  Except after a few seconds I will start to twitch on the both the yaw and pitch access.  The copter will be hovering and without touching the sticks it will take a small dip in one direction, then it will likely dip back the other direction.  Over the course of a few seconds the copter will feel more and more unstable until I bring it back down.

I was flying a virtually windless environment so that wasn't the issue.  Also, it seems from the logs that I've kept the vibrations very low, so I don't *think* that's the issue, although I would appreciate it someone could confirm that.  The Pixhawk is mounted on top of earplugs.

I should also note that the copter felt very twitchy and unstable in previous flights, so I lowered the values for both the "RC Feel Roll/Pitch" and "Roll/Pitch Sensitivity" in the Config/Tuning section of mission planner.  That resulted in a significant improvement.

I would appreciate if someone could take a look at my logs and give me their opinion.  If you compare Roll and DesRoll (and same for Pitch) you can see telling deviations.  But that's about all I know how to look at.

Thanks for your help!

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What battery are you using?  Your power module is indicating ~11.5v resting and 10.4v under load.  If this is a 3 cell pack it should be 12.6v when full.  Could it just be running out of power to stabilize itself?

I think that's very possible.  After doing lots more testing and adjusting, it turns out that the PID loops were way out of whack, so I got MUCH better results after adjusting those.  I also think the copter was out of balance, but unfortunately I wasn't logging ESC output values on these flights, so I couldn't check if some motors were working harder.

But even after all that, I did several short flights that went well, but noticed that the copter was getting progressively less stable as I did more test flights.  So that would indicate a deteriorating battery.  The battery I'm testing with is (a) too small for this machine and (b) old, so I think it's in poor shape.  Which would mean quick voltage drops.  It didn't know that this would cause instability.  I just figured it would mean having to land sooner.

Thanks for the advice.  I will do some more testing to confirm this.

Good to hear you are figuring some problems. Best to invest in better batteries.

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