Y6 Copter Extreme Gyration; "Pendulum" Effect, Hard Crash

Hello all,

I recently had a hard crash with my Y6 while attempting an auto flight.
My copter is a DIY Y6 Kit from 3D Robotics, with Pixhawk autopilot running AC 3.2. I have a medium sized payload (not near pushing the limit for this copter). I have been successfully piloting this copter for the past 6 months, and have completed roughly 50 auto missions without error. Several times though, when I put the copter into auto and it begins to climb to a waypoint, it begins to gyrate back and forth, with extremity of the gyration increasing exponentially each time (best described as the copter swooping side to side, fighting to maintain altitude, as if it is repeatedly over-correcting a roll or pitch value). Previously, when I observe this action, I immediately put the copter into stabilize and it corrects its attitude and flies stable. This most recent flight however, when I noticed the gyration, I switched into stabilize, and it stabilized only momentarily, then resumed the pendulum motion and lost altitude, until I cut the throttle and let it fall to a metal roof.
I have reviewed the logs, and cannot find an obvious reason for the crash. I would appreciate it if someone with more expertise and understanding could review my attached log to help determine the fix for this phenomenon.

Any help is appreciated. I regret not addressing this issue earlier.

Much Thanks
-Jake Warren

Looking at this, I can see that you switch to Auto, which results in a demand to climb. This increases the throttle higher than at any other point in the flight. At this point, the motors seem to not be performing well. Previously, the outputs were nicely matched, but when the throttle is high, they have a huge spread in throttle output. One of them is also clipping on the upper end, which is not good as it can lead to instability.

And this is seen, because the stability control gets really, really bad at the same time this is all going on.

I wanted to check your battery voltage at this point, but there is no data from the PM, so I can’t see anything there.

I think the issue is basically one of motor power, but I can’t tell you what the problem is based on this. It could also be that the propellers are spinning on the motors.

I think I understand what you’re saying, however I wouldn’t know where to start testing. What is the best way to test each of the motors performances?

Thank you very much for taking the time to look at my logs.


Well, one of the first things to test is the propeller tightness. Hold the motor and try to turn the prop, you should not be able to.

If it’s not that, then I have to guess that your system is underpowered for the payload you want to carry. Any time you have motors regularly hitting the maximum output is bad.