So I was flying the Gob500 yesterday and about 2 minutes into it I'm going some elevator, tail down tic tocs. Practicing my left/right movement control with ruddering during the vertical phase. Went right across the field no problems and was in the middle of yawing nose left to setup to tic toc back across the field when it just loses motor power.
No warning. No soft cutoff. The mains just start spinning down.
I'm vertical, tail down, about 30 ft off the ground.
I managed to get it leveled out, upright, and heading in a nose left (heading across my field of flight) orientation. So, power to the Rx and servos is fine. Only the ESC is out for some reason. The rotors were slowing down quick. I had the presence of mind to go to a little bit of negative pitch to try to preserve some head speed for when it got closer to the ground. But at 20ft up and practically no forward speed nor headwind there isn't a lot of distance to preserve, much less build, head speed.
So it got down near the ground very quickly. I flared back a bit and put some positive pitch into it so soften the hit, but it was going in, so I quick hit a little forward elevator to relevel it for impact. It hit pretty good. Broke the landing skids and brackets. Tail boom and fin looked okay. No evident blade damage (though i didn't do a close inspection yet). No frame damage from the looks of it.
Ordered up the stuff I knew needed replacing (going with some lynx fiberglass skids instead of the stock SAB CF ones, little cheaper). Will take a look to see what, if anything else is needed.
No idea what happened. There was an unusual beeping pattern coming from it. But I didn't have the presence of mind to take note of what it was. The Rx sat had a solid light so no connection or power loss there. There is a small spot on one of the motor lead connections where the shrink tube rubbed away, but neither of the others was exposed and the canopy is fiberglass so it shouldn't have conducted anything to cause a short or issue with the motor timing/ESC. Nothing was obscenely hot when I got the canopy off it. Battery was at 3.85V per cell, plenty to go. I haven't checked the ESC logs yet. Maybe it overheated or there is something in the log to indicate what happened.
Only difference on this flight compared to many others this summer was that I was using the highest rolling rate setting I have setup. I almost never use it, and never for an extended period. This time I was really laying into the cyclic on tic tocs, using as little collective as I could to maintain height and keep that tail looking as stationary as possible in the sky as I could manage. Maybe I overstressed the drivetrain and power system in a way I hadn't before?