Today was a test flight of the F550 and boy did it turn out to be eventful!
A little background. A while back I had a minor crash when experimenting with batteries to find out why I was only getting 4 minutes of flight time when I should be getting much more. Since I had to remove the top anyway I figured this was a perfect time to try move all of the electronics inside to give it a much cleaner look.
I got it all in there but the squishly little balls in the anti-vibration plate were heavily compressed (see picture) and I was worried that vibration would cause the APM Flight Controller (FC) to go a little loopy.
To quote the APM wiki.
High vibrations can lead to the copter rapidly climbing as soon as altitude hold is engaged.
I considered flying in the back yard but, since this was practically a full rebuild, I figured I had better give myself some room and there are lots of overhanging trees. One of the few smart things I did today!
I set up instead at a local field with plenty of room, confirmed I had a good GPS lock, and decided to launch it in “Position Hold” mode, which should use the barometer to automatically hold altitude and the GPS to keep it in the same location. the plan was to just let it hover until the battery was low.
I armed the motors, pushed up on the throttle and up she went!
She was climbing fast and at a height of about 30ft I backed the throttle off and it stopped right where I needed it…except…that never happened! Instead she kept climbing like a rocket and, at the same time, started moving away from me.
By now I had the throttle all the way down and she still climbed, topping off at about 45 meters (almost 150′).
Of course, I did what any self respecting drone pilot would do. I PANICKED!
After having it spin in place for a while I realized that it had sort of stabilized. It wasn’t climbing anymore and it was staying in place. But how to get it down? I had the throttle at minimum and it was just hanging there laughing at me.
Figuring that vibration was messing with the barometer I switched to manual mode (Stabilize). Of course…since I had the throttle at minimum that immediately turned all the props off and she dropped like a stone!
I quickly gave it throttle again, got it back up in the air, and after a frantic 30 seconds managed to get it back under control. I had to keep on top of it all the time but it was flying now and responding to my inputs. Phew!
It was about this time that I realized I never actually hooked up the little beeper to the battery so that it would beep when it was getting low. No worries though, I had set it to auto land on a low battery warning so I decided to just let it ride.
Unfortunately the jamming in of the FC seemed to have pushed it off kilter and it took constant backward / left pressure on the controls to keep it in place.
All was fine for a while until, suddenly, it took off for the sky at a great rate of knots with no input from me!, topping out this time at around 100′.
Again I put the throttle all the way down to no avail, and then (stupidly) put it in Stabilize mode again. And, just like before, it dropped like a stone again!
I powered up but this time wasn’t quite fast enough (perhaps because less power was available) and the best I could manage was a crash at a speed low enough to cause pieces to fly off, but not damage anything permanently.
It wasn’t all bad news. The flight time was better (7 minutes) but still not good enough. And the gimbal I had mounted to replace the one that went nuts every time the thing took off seems to be working perfectly.
Sadly though it looks like I will be spending a happy evening moving everything back on the top. Not hard to do…just a PIA.