Heri,
I understand your comments about the winds and I would agree to not change the servo trim values but increase the ILMI for pitch and roll to 0.1
For the system ID, I would like you to use this mode in each axis (pitch, roll and yaw). The general settings are the following.
SID_F_START_HZ, 0.25
SID_F_STOP_HZ, 10
SID_T_FADE_IN, 10
SID_T_FADE_OUT, 2
SID_T_REC, 90
In the LOG_BITMASK parameter, uncheck the FAST ATTITUDE setting. This will cause the system ID mode to collect data at 100 hz rather than 400 hz.
You would set SID_AXIS to perform the sweep in each axis
For the roll axis sweep set
SID_AXIS, 1
SID_MAGNITUDE, 3
for the pitch axis sweep set
SID_AXIS, 2
SID_MAGNITUDE, 3
for the yaw axis sweep set
SID_AXIS, 3
SID_MAGNITUDE, 5
The SID_MAGNITUDE sets the attitude maximum to 3 deg for pitch and roll sweeps. For the Yaw axis this sets the max yaw rate to 5 deg/s.
You never want to takeoff or land in System ID mode. I would suggest taking off in stabilize mode. Once you are in a stable hover, switch to system ID mode. This mode requires you to control the aircraft and keep it from hitting things. It is not designed to hold position over the ground. It is basically stabilize mode with the frequency sweep inputs being added to your inputs. Once 90 seconds has passed, switch into stabilize mode and land.
Hopefully you watched the videos in the autotune wiki about flying the aircraft while the frequency sweep is being performed. You will do a similar thing here except the sweep will take 90 seconds to complete. Initially the aircraft will drift quite a bit so ensure that you are flying in an open space. It may drift up to 10-15 meters initially during the low frequency portion of the sweep. As long as it isn’t constantly moving away from you, let it oscillate back and forth over the ground. If it does start to constantly move away while it oscillates, then apply a small constant stick inputs to stop it from moving away from you and keep it oscillating about one point over the ground. Once the frequency gets high enough the aircraft will stop drifting back and forth and will stay pretty stationary as it continues to oscillate in the axis being swept.
Be sure to do this on a fairly calm day (< 5-10 kph winds). The lower the winds, the better. If the winds are coming from a specific direction then have the axis being swept pointed perpendicular to the wind. for example, if the winds are coming from the north and you are sweeping the pitch axis, then point the nose of the aircraft to the east or west for the sweep.
Hopefully this all makes sense