Discussions

I have several questions and issues I ran in to while tuning my plane this weekend. I'm flying a Finwing Penguin and with the stock PID's, it seemed to fly just fine but I wanted it tuned the best I could get. I had a friend fly the plane while I adjusted the tuning in flight and that seemed to work out well but there were a few things that I was worried about with tuning. At this point, all we did was the basic roll, pitch, and yaw tuning and we'll work on airspeed and TECS once RPY are taken care of.

Before I get started, I have a basic firmware updating question. I'm running 2.74b right now and doing all the tuning using that firmware. I would like to go to 2.75 but it seems there are a few issues with the auto airspeed calibration and battery voltage monitoring. (EDIT: Looks like 2.76 fixes airspeed and DCM but not sure on the battery monitoring.) I'll keep an eye on that but my question is, when I update the firmware on the APM, will that require retuning? Do I need to first save the parameter settings before upgrading and then restore them back? I assume that unless there was a change to how some of the control algorithms work, most PID's that I set on 2.74b should work just fine on 2.75/2.76 right? I ask now because I don't want to go through and do a whole lot more tuning only to find out I have to start over again.

On to the tuning background and questions.

First off, when you do tuning, under what conditions should it be done? Ideally, no wind would let you see any wobble/rocking/porpoising very easily but it's not often there is no wind. I know I'll be flying in some wind most of the time. I assume if you tune when the winds are 5-8 mph, it won't work as well if you have say 10-15 mph winds right? How do you tune to try and get good performance in most wind conditions?

My tuning was done in low winds, so around 3-6 mph is my guess.

Roll tuning seemed to work fine. I watched the computer the entire time watching for it to show any overshoot on the graphs while the pilot watched the plane. I realize now that he had it up really high so there is almost no way he could have seen really small wobbles so it's something I may have to do again but regardless, roll seems fine at this point. I didn't mess with RLL2SRV_T_CONST or RLL2SRV_MAX for roll_speed tuning. I assume if it doesn't roll as fast as I want, I can change the time constant parameter correct?

My final parameters for the PID's for roll were:

RLL2SRV_P: 1.3

RLL2SRV_I: 0.125

RLL2SRV_D : 0.1

RLL2SRV_IMAX: 500

Reasonable enough? I know it's airframe dependent but if something is way off, that's what I'm most interested in finding out. It seems that my P term seems much less than the Penguin in the 2.75 release thread but maybe he has more/less weight than me?

For pitch tuning, we seemed to have more issues there, mainly because I have no idea what to expect for typical PID values. I followed the pitch tuning methods in the wiki. Using Method 1 to get the PTCH2SRV_P gain set, things seemed to work fine, granted the P value was very high at 2.8. I tried testing to see if the nose changed height in banked turns and it seemed to do just fine without gaining or losing much altitude based on what I saw on the MP and what my pilot said.

Then I continued to Method 2 and increased PTCH2SR_D and came up with 0.025 after we halved the value we had when we noticed some wobble/porpoising.

Finally, we moved to tuning PTCH2SRV_I and I bumped the value all the way up to 2.8 and then dropped it back down to 2.0 because after raising it that high, we couldn't see any sort of wobbling at all. It's not normal for the I-term to be so high is it? If not, why would I not be seeing any wobble at all when increasing it that high?

My final parameters that I settled on (but are doubting) are:

PTCH2SRV_P: 2.8

PTCH2SRV_I: 2.0

PTCH2SRV_D: 0.025

PTCH2SRV_IMAX: 500

Any advice on these gains would be appreciated. I seems way out of whack, D seems quite low, and P seems higher than the one in that same 2.75 release thread.

For yaw tuning, well, I didn't get to that point because I looked for the YAW2SRV_SLIP, YAW2SRV_INT, YAW2SRV_RLL, YAW2SRV_DAMP parameters to adjust and couldn't find them in the full list of parameters. Is there no yaw tuning that needs to be done in 2.74b?

Once this tuning is taken care of, then I plan on doing the airspeed tuning and move on to TECS.

Finally, there were some errors the MP would tell me periodically. I will say that when I opened the MP that morning, it said there was an update so I updated and now I'm on v1.2.85 build 1.1.5049.36165. I didn't notice a problem when I ran the previous version.

Anyway, when I connected at the field, on the HUD, it said there was "NO RC Receiver" but the MP wouldn't speak anything about it. I had full control over everything on the ground and couldn't figure out what the problem was so I just went up and disregarded the message, although it worried me a little.

As I flew, I had a Bad Compass Health warning come up multiple times and MP told me and then immediately after, I got the NO RC Receiver warning verbally at that point. Neither warning seemed to affect anything. My questions for the warnings are:

1. Why am I getting the NO RC Receiver warning when everything is connected and running just fine? What does it key off of to get that sort of warning?

2. What is the Bad Compass Health warning I'm getting ? The APM is installed in the fuse in the middle of the plane just behind the CG. Above it by 2-3" is the ESC and then the motor is another 2-3" above and behind the ESC. It seemed to only happen when I was banked at one part of the field.

I'm finally glad to have a bird in the air with an APM after wanting to do so for the last 3.5 years and not being able to. I hope as I get more familiar that I can help others out in some way. I do still need to get the MinimOSD installed but that's a separate issue that I'll deal with as I know some resources on how to get me up on running on that.

Thanks for reading through all my questions!