Drone will flight fine for several minutes then becomes very unstable and not respond to controls, usually crashing. This is not a fly away scenario, when unstable it stays in the general area. This happens on average every five or six flights. If reading the data logs correctly this does not appear to be vibrations, but I would appreciate a more experienced analysis of the data logs. During boot up usually get GPS speed errors and bad AHRS, once home is acquired errors do not reappear and drone will arm.
There were several errors that initially occurred when arducopter installed on Kopis
GPS would only find 3 to 5 satellites, seldom acquired a GPS lock.
High GPS HDOP
Compass calibration outside of recommended parameters, example reading 234 -90 - 225
AHRS, IMU and EKF errors
Powering down the video transmitter board eliminated most errors.
Listed below is steps taken to correct errors
Elevated the GPS/Compass combo.
Protected GPS and Compass data leads from RF feedback using Ferrite Core Bead Chokes.
Placed EMF/RF shielding tape under the GPS.
Powered the GPS/compass combo with independent power regulator with electrolytic capacitors across input and output power leads.
Raised the top plate, this allows the video transmitter board to be raised putting a little more distance between the boards and room to insert EMF/RF shielding tape between the two boards with attached ground wire.
Video transmitter board receives power from the flight control board, to block any RF feed back on the power leads a 30 pf capacitor was put across the power leads.
Removed the default video transmitter antenna which was within one inch of the flight controller and replaced it with a SpiroNET stubby antenna. This moved the radiating part of antenna about 3 inches away from the flight controller.
Enclosed the FC board to minimize prop wash effect and block sunlight from hitting the barometer.
Now with video transmitter board powered on the drone will get GPS lock and acquire home position with good satellite count. Compass calibration is within recommended parameters. But still having some problems.