You know, that "tail heavy" typical up, stall, down, and again, and again behaviour ?
Well in manual mode I do not have it, it is perfectly stable. It Took me a full day to get there.
So I was expecting the stabilize mode to be a piece of cake.
But as soon as I set the APM to stabilize, then the plane acts as if it was tail heavy. And I know it is not, CG perfectly placed.
Does that mean that APM correction frequency is too slow ? Should I increase P or I ?
Or is it what you call "oscillating" on the PID tuning page and I should set P down ?
Also, I have pitch min / max value set-up at 800 / 2200 for maximum control.
Should I narrow it back to 1200 / 1800 ?
Thank you
Replies
I found a way. In short :
- Set trim_auto variable at 1 ;
- Fly in manual mode and make your plane perfectly stable ;
- Now switch to stabilize mode or FWBA. You should see no more differences when switching
- Set trim_auto variable back at 0 for safety reasons.
That's it. Make sure you check out trim_auto on Wiki before flying
Okay, looks like it was what I thought it might be as you had to have trim in the radio to get it flying right as it wasn't mechanically trimmed to begin with. That's what I usually work on with a flight without APM before installing one. In fact, I'll be going out to do a re-maiden of my Penguin this evening after I had to repair it after a collision with a tree and the subsequent damage with it hitting the ground.
The auto-trim function is quite nice isn't it? I now have one on my radio as well for flying models without a FC and that will be very handy.
Glad you got it squared away!
You should decrease P for pitch and see how it goes. There's an entire tuning guide that explains how to do it and if you follow it, it's very easy to tune. I don't know if you did but don't mess with the stock PID's and leave them. They'll work alright to begin with but can be made better through tuning as explained in the manual.
You should be tuning in FBW-A first as tuning there will take care of tuning for anything else like stabilize or the auto modes.
http://plane.ardupilot.com/wiki/roll-pitch-controller-tuning/
Just read and go through the manual step-by-step and it'll answer almost every basic question out there.
Thank you. My problem is the vocabulary used :-)
On a plane, is an oscillation a slow up and down move or is it some fast shaking ?
Can I detect an oscillation on the logs ?
Both are oscillations. If it overcorrects too much, then your P term is too high. If it just keeps going back and forth without you doing anything, it's probably an I or D term but I'm still not too sure how those work yet but if you use the defaults, you shouldn't have that problem on a properly set up Penguin. Fly the plan with no APM first, make sure it's trimmed out mechanically (not using the radio trims), and then add the APM. Go in little steps instead of all in because then you'll have issues figuring out where your problems could be. If it's porpoising that badly in Stabilize, my guess is you have some trim settings that could be causing issues too that you should fix mechanically. You shouldn't trim the plane with the radio if you're using an APM so make it right before using the APM.
If you follow the tuning guide and tune in FBW-A, then you go through tuning each step. Start at the default PID settings and go from there. I never had the porpoising with my Penguin when I used the stock setup and that's with a stock plane using a 5000mAh 3S battery. If you start with the defaults and don't mess with anything beforehand, then you should be able to get through the tuning just fine without any issues.
Sounds like you have stabilize and manual switched. I don't think there is anything adjustable in manual.