1600 hexa not stable at roll axis

ArduCopter Copter 3.4
1

Hello all, the hexa i am flying with now is 1600mm, around 7kg without payload and 12kg with payload, and it is not stable at the roll axis. What will be the most common issue?

I am attaching two flights,

  1. without payload 2018-03-02

  2. 5kg payload strapped to the bottom 2018-03-05 https://youtu.be/hA1cP8OFWN4

I am suspecting the PID gains being unsuitable, but are there any other concerns from the flight log?

Log files:


2

You are right in your suspicion of the PID gains being too far out.
For such a large copter have you adjusted your filter frequencies ?
Might make a big difference.
I tried autotune with a copter that size, once, without adjusting the gyro filters and it just flipped over on about 4th or 5th tuning twitch.

53%20am
Screen Shot 2018-03-07 at 6.32.53 am.png2534×954 341 KB

As you can see desired and actual were chasing one another and getting progressively more out of sync.
Have a read of the Autotune section of the Wiki for directions on setting up for large copters so you can get it stable enough to do an autotune.

3

I just checked my params, and apparently my ATC_RAT_PIT_FILT was 20. I remembered setting it to 10 but maybe I have reset my parameters and thats what lead to this issue.

Thanks for the pointers, I will change the filter to 10 and try altitude hold mode to check for stability

4

Start with the aggressiveness at 0.05 as well.That can damp down the odd nasty surprise.