So right now I am working with a 450 that has an odd issue, with the stock throttle accel settings after a few seconds of great flight it will start jack hammering in flight.
here is the video of the jack hammering: https://www.youtube.com/watch?v=zsNNitA1YLM
and here is the log: feedback log
so we turned down the throttle accel p and the throttle accel i keeping the 2:1 ratio suggested here: http://ardupilot.org/copter/docs/tuning.html#tuning
and here is the video: https://www.youtube.com/watch?v=r_gCLHCIvJA
it may not come across but the whole time I was holding the collective up and it started pushing itself down before I cut the motor.
here is the log: odd alt
What might be causing this weird behaviour? can anyone help?