hi leonard, how is it like doing the autotune a pixhawk with the EKF on? Is it fine to do that?
Your copter is very unstable with the pids you are flying with. Autotune didn't cause your problem, it just kicked it off. I can see after autotune does each test that the copter overshoots almost as far as autotune goes in the first place. This means your copter is right on the edge of instability. I would drop your Rate P terms by 50% and try again.
Autotune may not be able to set the parameters low enough for your copter though.
I will look at improving this further in the future.
Yes, I'm beginning to see that my copters have some issues. I have 3 builds which are identical to this and each of them have this massive instability issue. I have not had time over the last few weeks to get back to the tuning but will follow your advice on dropping the Rate P terms even further. Here is a question: If I lower the Rate P terms until the copter is "stable" should I then start working on the Stabilize P (Roll and Pitch) terms until the copter gets twitchy and then drop them down a bit?
Another really weird thing happened on my last test flight of the copter mentioned in the above comment, it was flying great for a while in altitude hold and stabilize and when I finally got the courage to switch to loiter, it seemed to fly perfectly then too until I turned and flew into the wind where all of a sudden it seemed to stop moving forward, pitched backward, pitched forward, pitched backward... well, you get the idea, it was doing a pendulum until it looked like it was going to crash at which point I switched out of Loiter. Since most of my flights are in Auto (I use UAVs for Aerial Mapping and 3D modeling), I'm a little concerned about the relationship between very low PIDs and Loiter/Auto functionality. Is it safe to assume that as long as the copter flies nicely in Altitude Hold and Stablize that it will perform properly in loiter/Auto too?
Could you tell me the size and weight of your copters and post a photo or two.
The basic principle is each pid loop stands on the next so if your Rate tune is bad everything is bad. Also it isn't enough that the copter flies well in Stabilize and Alt_Hold. You need to be able to be rough with the sticks to be 100% sure auto and loiter will work well.
If you copter is very slow to respond in stabilize and alt hold then you may have to back off your auto pids to ensure you don't get an oscillation like the one you described.
The general approach is to find some very stable pid parameters for rate and stab pids, then use Autotune to get the best out of your copter. After that the defaults tend to work well.
The Pixhawk and the EKF have no effect on autotune.
Here is a log of one of my excessively long tuning flights.. (I actually went down after 11 minutes because the battery pooped out.. I had my telemetry volume turned down and didn't hear the battery warning).
My frame is the standard Hex sold by 3DR. It has 880KV motors and an aging 5000 mA 4S battery. I had just replaced my APM2.5 with a new APM2.6 controller with an external compass & mag. I flashed it with 3.1 firmware and was using the default PIDs. I was hoping autotune would find the 'right' settings.
Successful auto tune, I think.
Just took advantage of a rare windless day and did a successful auto tune. The quad flys OK after saving the new PIDs but they are very far from the original default PIDs. See attached picture of the new ones.
Question is, are these OK or did something go wildly wrong? The quad flies OK in Satb and Loiter but past issues in Loiter only turned up when it was windy, so I can't test for that today.
3DR 2013 quad, 880 motors, 11 inch props, flying at 6300 feet elevation (not from from Spark Fun), firmware 3.13, APM 2.5.
We have a 5000ma battery on the bottom and an Action Pro cam on a pitch control mount.
I see no one else replied, and I just had success with autotune, so let me toss out a couple of issues I worked through.
I had to connect a wire from the radio AUX2 output pin to the CH7 input on the APM2.5. That gets the signal from CH7 (AUX2) on the DX8 into the APM.
Once that wire was in place I could use radio calibration in mission planner to see the pwm value change when I flipped the switch. I noted on the DX8 AUX2 switch that position '2' was off and position '0' was on in regards to enabling auto tune. Those aren't mentioned in Randy's vid.
The HUD in MP will show Auto Tune when you have all the setup correct and flip that CH7 switch. And as in the vid and comments, it displayed "complete" when it finished.
The rest of the setup is in the vid which was quite helpful.
I also noted that using a 5000mAh battery on my 3DR quad with an ActionPro camera it took every bit of 10 minutes and getting close to battery fail safe to complete the auto tune. I had nearly zero wind. When I had tried it with up to 5MPH wind I could not complete it because of the time it took to keep bringing the quad back to the start point. I'd estimate it would take about twice as long because I spent as much time keeping it from blowing away as it spent in auto tune mode.
Today my first autotune with Arducopter 3.1.4 on APM 2.6, esc's 40a SimonK, MK3638 motors, props APC 12x3.8, 4s battery and total weight 3.5Kg.
1,30 min for roll, 1.30 min for pitch. Why it was so fast ?
I like final result, very smooth flight.
Ciao - Giuseppe
Today first Autotune on Pixhawk with firmware 3.1.4, esc's AFRO30a (with ground connected ;-)) T-motors MT2216-900kv, props Graupner 11x5, frame clone Mikrokpter XL2 (square frame), batteries 4s, total weight 3.9Kg.
1.10 minute fot roll 1.30 for pitch.
After small flight, very good response.
here video (with begin pid's and final pid's)
Ciao - Giuseppe
Can't figure out why autotune won't start. I've tried both CH7 method, and setting it as a normal flight mode. I'm using APM 2.5 with APM 3.1.5 . Any ideas?
Nevermind. Was using the wrong switch set up for ch7 on my new TX :-p . Realized when I actually looked down at my transmitter. However, I didn't get autotune to work as a "normal" mode.