Ok, now I understand what you're saying about the angles. I was in Stab mode, which only controls the attitude, but not the thrust/altitude. There is an Alt_Hold mode, which is the same, but also controls altitude. I could have used that but just didn't. I should do some test flying in that mode to see how well it works. To be honest, I'm still learning to fly a heli, and I want to make sure I know how to control it the old fashioned way without totally relying on the system. I have flown airplanes for years and am pretty good, but the transition to heli is a challenge. The one really low pass was much lower than I wanted, but I have to rewire my brain. I was pulling back on the "elevator", but it was still losing altitude. In an airplane you just keep pulling back. The heli, I should have increased thrust. On an airplane, if you're aimed at the ground and don't want to be, the last thing you would do is throttle up!
I came within about 2 feet of the ground there. One of those "Heh, I meant to do that" moments!
Now, something else that I want to do is create a rudder control mode called "weathervane" where it intentionally controls the rudder to have the tail follow the ground-speed heading of the heli. This would simplify things and allow you to fly it more like an airplane. Put it in Alt_Hold and just cruise around. It would be really nice for FPV, or shooting a video where you're following a moving target.
Yes, it's slowly becoming less and less HK, and I'm getting out of that completely. It was necessary because I crashed a lot while developing the code. But now that things are working better, it's causing more problems. I am building up a heli that is basically a 550 stretched to 600, will probably go to 700 eventually. I want the lighter weight of the 550 frame with direct to swash servos. It's being built with all high quality stuff. Tarot 2mm frames, KDE parts, Heli Option, RJ head, etc. It'll be a bit heavy because everything is aluminum and thick CF, no plastic. But I'm trying to build something that is "industrial" using COTS components. At least as much as I can within my budget.
The tail drive shaft is actually a genuine Align already. And I've used their main gears but honestly didn't find them any better than the HK. I've been thinking of using this machined gear, what do you think?
http://www.kdedirect.com/TREX700MDGM07.html
I totally get what you're saying though. It's really obvious. This was a fresh, full rebuild, and the first flight was fine. Then the vibes got worse and worse. I think it's the gear mesh as you say, and I probably already blew the tail drive bearings. I suspect I'm putting too much tension on the belt because I'm going through these things really fast. Doesn't help that they're cheap bearings.
Still, I think that the system should function properly if the heli reasonable, which it is. I can fly it in full manual no problem at all. So if the system causes a crash that didn't need to happen, it sort of defeats the purpose.