Hello All,
First off, let me say that I'm new to APM; I've been following the developments here on diydrones for a couple of years, yet I never actually got myself motivated enough to try building an APM setup until now. So, I finally pulled the trigger and built up my bixler 1 with the latest version of APM.
I'm coming from the 'KK2/OpenAero' world for basic rate-based flight stabilization for a plane (no autolevel, just gyro-based PID corrections for all 3 axes). I was satisfied with OpenAero, but decided to make the switch over to APM 2.5 mainly in order to have RTL functionality. Plus, I figured it would be cool to experiment with some of the other features for FPV missions (waypoints, CRUISE mode, mission planning&logging, etc).
Ok, so today I had my maiden w/ my bixler/APM, and I have to say that I was very disappointed in the flight characteristics. Yes, APM "did what it was supposed to do" in pretty much every flight mode (had some issues with loiter, but was probably due to a configuration problem). So, my complaints aren't so much that APM had any major problems or glitches; it was more that I felt the experience was just too 'toy-like' and restrictive for my level of flying. The STABILIZE and FBW* modes were no fun at all. I felt that ACRO mode was probably the closest approximation to a 'proper' stabilized RC flying mode, but even *it* was way too limiting and too much of a hassle for someone who prefers to actually fly the plane (without any 'training wheels' attached).
So, basically, I'm looking for a flying mode in APM that's based more on a 'standard' rate-based flight stabilization (something between ACRO and MANUAL); a run-of-the-mill PID controller stabilization for all 3 axes (yaw, pitch, roll), without any 'attitude hold', 'auto-level', 'rudder-aileron' mixing, throttle control, etc....none of that stuff...I *know* how to fly my plane, so I'd just like some assistance from the gyros in smoothing it out & nothing more.
I'm a developer, so I went ahead & dove into the APM code on github. I was able to see how the flight modes are structured, including ACRO. Perhaps I may have missed something, but I didn't readily see any obvious way to disable the additional features/flight processing in ACRO (such as 'attitude hold'). So, I'm assuming that there isn't currently a mode that fits my needs, correct? What would need to happen for something like this to be added to APM? (i.e., a simple rate-based stab. mode w/o any additional 'flight assistance' features/processing)
As of right now, my bix/APM setup feels pretty much useless (it's no fun to fly at all, and I'm even starting to miss my OpenAero setup). So, I'm seriously tempted to start hacking away at the code in an attempt to create a new, custom flight mode for APM that only does the rate-based, PID stabilization for Roll/Pitch/Yaw. However, I wanted to see if anyone had any feedback on this, and/or If someone has already developed something in the past (if so, would you mind chiming in & sharing?).
Any advice/feedback would be greatly appreciated.
Replies
Hi,
There is no rate-only mode currently for airplanes.
ACRO is a strange thing (IMO). What is does is integrating stick input to target pitch and roll values. So it will attempt to fly along a path that you can make more or less steep with pitch, and at a bank angle you can crank up and down with roll. That is also why there are all those warnings about stalling it in the manual, because it will iron out the little warnings of an imminent stall that you usually get - that you have to pitch up to hold the nose up - and will eventually stall hard. I implemented the same myself on a different controller some time back and soon stalled my otherwise very well behaved T-26 so badly that the nose broke off...
The best approx. to rate is stabilized mode. This targets to hold the plane level, but adds your stick input at the last moment (the stick values or their differentials or integrals are not getting into the PIDs). If you set the Ps and Is to zero, you should theoretically have rate stabilization (the D of attitude is rate). I cannot remember if D is body axes or global axes - hopefully body.
If you hack that rate mode, can I have it too :) ? Or feel free to PM me about it, I believe I know just about how it can be done.
Regards
Soren