Good day everyone.
My first post in this forum. Hope everyone is doing well.
I am designing a drone which FC is tilted 25 degrees in reference to the frame. So the FC is not sitting flush with the surface, it having an angle.
I am not sure of how the drone should be calibrated in this case. If I put the FC orientation-non and do the calibration by the frame as reference will it internally recognize that its FC has a pitch 25 degrees?
Hi Rubski, welcome to the community 
Normally FC orientation is set with AHRS_ORIENTATION as documented here, but that is limited to 45° increments.
For orientations outside these 45° increments there are the custom roatation parameters, where you can set
CUST_ROT_ENABLE = 1 (enable custom rotation)
CUST_ROT1_PITCH = ± 25 (pitch offset 25°)
I am not sure if a positive value means pitch forward or pitch backward, but if you get it wrong the FC will probably complain and not calibrate.