Copter-3.6.6-rc2 has just been released for beta testing and can be downloaded using the GCS’s Beta Firmwares link. The changes vs -rc1 are in the ReleaseNotes and also copied below. This release includes one critical bug fix (please see below).
Changes from 3.6.6-rc1
- Bug fixes
a) EKF compass switching fix for vehicles with 3 compasses
b) CAN fixed on Pixhawk4 and PH4-mini
c) Mini-pix uart telem1 and telem2 reversed
d) Divide-by-zero protection if _FILT_HZ params set to zero
e) Guided_NoGPS skips GPS pre-arm check
The critical change is the EKF compass switching fix (highlighted above). The issue is that on systems with 3 compasses (which have become very common) the EKF could continue trying to use a “bad compass” even after it had determined that this compass’s heading doesn’t match the GPS and IMU. This can lead to the bad compass negatively impacting the vehicle’s position and/or attitude estimate leading to a loss of control and a crash.
Although this bug sounds very scary (and it is) the worst case is quite rare. A much more common symptom of the problem is many messages from the EKF warning that it has changed the primary compass. At least two beta testers have reported seeing this less serious symptom.
Any and all beta testing is greatly appreciated! If things go well we hope to release this version as the official/default version next week.