After nearly two years of putting around with no nasty surprises my heavy Hex, "The Witch" has been behaving badly and yesterday gave me a fright.
A couple of weeks ago I moved up to 3.1 from 3.0.1 and in test flights noticed that there seems to be some sort of coupling going on between yaw commands and pitch/roll, because whenever the ship is in Loiter mode and holding position and even a gentle smallish (20-30 degree) Yaw input is commanded there is significant lateral movement. I posted a question about this on the new Arducopter forum and have gotten zero support there, so yesterday I decided to make a video of the behavior and to post it here. There's still no video because of the below event, but I would sure appreciate some help with that.
So, as I was preparing to launch yesterday with the intention of making that video, here's what happened (clip is in HD on Youtube).
I was peering down at the indicator lights while arming to make sure I had solid blue (I now hate even more not being able to see those lights at a safe distance). That was a nasty scare (see Oliver jump!) when the Witch abruptly spooled up under my face, with no input from me and zero control. Neither the spool-up nor the shutdown was commanded by my Tx. Flight Mode was Stabilize.
As is seen from the log (attached, and a screen shot at end of video) the Hex thought it was landing. The only failsafe set to "Land" was GPS loss. One other failsafe was enabled, Throttle (to RTL). Geofence was also enabled with 100 meter distances and RTL action."Check on Arming" was disabled.
Location of incident was our AMA field, very GPS friendly with no history at all of glitches, multipathing, etc., as it's far from buildings etc.
Firmware was 3.0.1, I had dialed back to that from 3.1 a couple of days ago while hunting for the source of the Yaw problem (it made no difference). APM 2.6 with Ublox GPS and compass both on stalks, excellent vibration numbers, never crashed, no question of inadequate power.
Log file attached.
I'm hearing that this may not be the only incident of its kind recently. I'm pretty unhappy about it, and until I at least find out the cause I consider flying this ship, in which I have a lot of time and money invested, rather risky. I'm hoping for practical advice here to prevent a recurrence. Meanwhile I'm bumping the firmware back up to 3.1 and disabling all the failsafes and Geofence.
Thanks for looking!