Is there a center of rotation point on the PixHawk that should ideally be aligned with the trad helicopter main shaft? I’m thinking that this is at or very near the point where pitch, aileron and elevator reference would be. Maybe this makes no sense or is a not-required level of precision… I’m not an aeronautical engineer. ( I am an astronomer but I expect robotic celestial navigation is a bit beyond PixHawk capability this month. Maybe an upside down PX4Flow could do this. Hmm…)
Ideally the mpu6k on the board should be at the center-of-gravity of the vehicle. If it’s off from this point then some rotation will be misinterpreted as an acceleration. In practice though it doesn’t matter if it’s a bit off…or even quite a bit off unless you’re doing a lot of rotation over a long period of time. So for example if you put the pixhawk on the tail of the copter and then did a lot of yawing for 10seconds it’s attitude would go off and I suspect it’s loiter performance would be very bad. If it’s placed within 10cm of the COG I doubt you’d see any problems though.