I am definitely not still shooting for say, .2 on the P gains anymore. Now that I am a bit more comfortable with the system I have a better feel of what's going on.
Let me see if I can explain my thoughts correctly. Please excuse the FBL reference, it just what I know and have worked with many so it's a good benchmark for me.
- Say I am tuning my new Goblin 700 with a Spirit Pro.. Ive set up the system and gone with middle road gains. Now I start to bring up the cyclic gain until I see ossicilations and back it off a couple points, not unlike what i'm doing with the Pixhawk. Now the heli feels locked in, but, I have a bounce on the pitch axis. Now if I just drop the head gain down quite a bit, the bounce goes away but the heli is not nearly as locked in.
What I do now is leave the gain where it is and go into the software and employ the "Elevator Filter". Now the bounce is gone and I still have that locked in feel from having the gain a bit higher. I have no way of knowing what sort of filtering they are using, and everyone is so tight lipped about their firmware I will likely never know. I understand that I guess as you just have to look to something like the KBAR that was a direct ripoff of the VBAR, firmware and all, to see why they are so tight lipped about their filtering schemes. One thing is for certain is that it is all coming down to firmware and filtering of the signal. Newer units are using the same sensors that something like the Pixhawk Is using so the playing field is pretty level, as I have said before it is all coming down to their firmware and how well they execute it.
- Example 2 goes like this, I had a vibration prone helicopter. It was off the charts so no matter what I did I would have unwanted tendencies if I tried raising the cyclic gain to a reasonable level. I go in the software and select "advanced signal processing" and viola, I can now raise the gain by 50% and have a locked in helicopter regardless of sensor saturation because of the terrible vibes. I would absolutely love to know what they are doing the filter the signal, as I am certain it could be used to great effect with Pixhawk.
I am not looking to have my UAS feel anything like my 3D helicopters, in fact I want it to feel the opposite, but all that aside I also don't believe I am anywhere close to where should be with P gain. It just doesn't feel like I am totally in control when flying it, it has a mushiness to it. The VFF will definitely sharpen up the response of the helicopter, but it just doesn't feel like its locked in with high VFF and low P gains. Nothing about my helicopter feels smooth. I am quite smooth with my control inputs, I don't jab the sticks, but it feels like the helicopter is jumpy and not dampened at all. I have High I gain and some D in there, but I am starting to think a lot of my issue has to do with such a small P value.
I played around with a disposable quad recently. I set the gain values of P I and D to sort of mimic what I have on my helicopter and although they are two very different airframes, I found I had the same type of control response with High I, and low P and D. I am not well enough versed to look at the data and compare the results in a meaningful way so I have to base this all of feel, but I can say for sure similar setting I had on that little quad with the PID's resulted in that same "tightened up rubber band" feel.. Just nothing smooth about it, no feeling of control. It just plain feels unbalanced if that makes sense?
I truly believe better filtering will allow Pixhawk to perform far better with traditional helicopters and soon I will see if a notch filter Improves things. I just don't like the fact that there is such a wide gap between when small instabilities start and when the big P gain oscillations pop up.