I am tuning a 15 kg X8 configuration copter with 22" props. I have done autotuning and the machine flyes very well and stabile in stabilize, altitude hold and loiter mode except when it is descending with trottel very low or all the way down, then machine sometimes get very instabile and sometimes it falls a couple of meters in the air with side down (not same side down everytime) or copter wobbles from side to side until I give more trottel then it stabilizes instantly. The CG is not far from middle of machine. This instabile descending shows up in both stabilize, altitude hold and loiter mode and it seems to get worse in windy conditions and/or when I give any bigger pitch, roll or yaw input while descending. It feels like the copter does not react fast enough to stabilize the axis while descending. I have tried a lot of manual tuning like raising the ATC_THR_MIX parameters to maximum without much difference and also done new autotuning without any success. Also tried to raise the min trottel and tried to slow down the descending speed without any difference. The 22" props rotate at low rpm (about 2500 rpm hovering with 45 % trottel). I would be very thankful for some help and ideas on this.
you need to post your logs and parameter file to give it a look.