Replies to This Discussion

DeveloperPermalink Reply by Adam Rivera on June 21, 2012 at 11:41am

Question for anyone: I would not consider myself a "PID beginner", but I can always use more tips and tricks from other experienced users. My question is this, Given that the Stab P gain could change the way that the RATE P/I gains behave, how can you decouple them for the purpose of tuning? I have tried several strategies and the one I use most often is below.

1. Set Stab P to 1 so it is not a affecting the desired rate at all.
2. Fiddle with Rate_P until the fast oscillation is visible and then reduce a little so it goes away
3. Increase Stab P for more responsive controls

The problem is at number 3. If you increase the Stab P, the desired rate increases which increases the rate error which seems to induce fast oscillations again. Am I on track here? How do you find the balance between the two terms? Right now I have my copter pretty well tuned, but I feel that I stumbled upon functional gains rather than fully understood the process.

• ▶ Reply

Permalink Reply by Dave C on June 21, 2012 at 2:22pm

Yep that's pretty much what i do, but also do this too:

Slam a load of rate_d in, (until you see 'the twitches', and when I say 'a load' I mean 0.001 at a time until the twitch, then try to reduce vibration and try again) so that when you increase stab_P it just feels more locked, then i fiddle with _I till it feels right when you grab it by the leg (simulating wind). 

However this approach is derived from flying experience rather than understanding of what's actually going on so yup, I'm all ears too :)

• ▶ Reply

ModeratorPermalink Reply by Dean Wynton on June 21, 2012 at 7:39pm

Rate mode is best tuned in Acro mode as it only uses the gyros, once you have it behaving quite well in this mode you can switch into stab mode and tune that, at least thats how I do it? I wouldn`t recommend this method for anyone that is not comfortable flying though? as a badly tuned acro mode can be a handful. If you go too high with rate p it will actually make the machine less responsive and have a delayed reaction to input...

Stab mode use both the accelerometers and gyros, Stab p is for tuning the accelerometers

• ▶ Reply

Permalink Reply by steve F11music.com on June 21, 2012 at 8:16pm

I'm using Planner 1.1.93 mav 1.0 and with the new config screens I'm not sure about my loiter or yaw settings. First I noticed in section ArduCopter Config that my loiter P=0, I=0 and IMAX 30 but when I go to other section ArduCopter Pids I see other settings for loiter which are 2.4 | .08 | .4 | IMAX 30.

And regarding YAW, for the first time I tried to take off in ACRO mode to try and tune that and it quickly does a fast yaw even though it is very good in stable mode. SO I checked my Rate Yaw and it's .13 | .0 | .002 | IMAX 50

and in stabilize Yaw it is 8 | .01 | IMAX 8

Is this right or is my acro spin caused by something else?

• ▶ Reply

DeveloperPermalink Reply by Marco Robustini on June 21, 2012 at 11:37pm

Auto mission and yaw:

Council to include this define in the config if you want a better precision during waypoint mission, especially when the quad arrives on each waypoint.
This also allows you to move the yaw throughout the mission directing an hypothetical cam in the desired direction without compromising the mission.
I personally think that the direction of the nose should be completely independent, especially if you want to take pictures or video.

#define AUTO_YAW YAW_HOLD

Many users have asked me the flight parameters of my quad, they will post here in the week.

Bests, Marco

• ▶ Reply

DeveloperPermalink Reply by Randy on June 22, 2012 at 11:42am

Marco,

     I'm planning to add this kind of yaw functionality in the AP_AxisController code which I hope will go into trunk within 2 weeks.  The way I plan to make it work is that when you go past a way point it will point to the next one..but if you then provide some user input, it will give up on trying to adjust the yaw and you will have full control.  It will try again to take over the yaw at the next waypoint..I was alternatively thinking of making it take back yaw control if it gets no input for 10 or 15seconds.

• ▶ Reply

DeveloperPermalink Reply by Marco Robustini on June 22, 2012 at 3:18pm

Sounds good Randy!

• ▶ Reply

Permalink Reply by Bruce Jones on June 21, 2012 at 11:38pm

Over the last 4 days I've probably gone through 20 or so batteries with my tricopter with an APM2 running the latest 2.6 software.  All-in-all it's been a really great experience.  Last night especially was a ton of fun.  I was using Flight Planner and flying all kinds of fun waypoint formations.  It was great!  And then tonight happened.

I went to the same location today as yesterday, had the exact same setup, nothing different except batteries were charged up.  I took off and everything seemed fine in stable mode, so I switched to auto thinking the simple waypoint plan I'd just loaded would be quick and easy.  Instead my tri headed off towards nowheresville like a rocket.  After a couple shocked seconds the tri had probably flown 500 meters away and up to a height of 100 meters.  I switched to RTL (which had worked so nicely the last couple days) and the craft veered 90° but kept on going.  I switched to alt hold and luckily it stuck.  I then slowly worked it back while trying to get my heart rate down and wondering just far the range is on my Spektrum system.

I reloaded the waypoints, checked to make sure they were loaded, triple checked all I could on the computer and tried again.  Similar response.  I did this 4 times, each time almost loosing the tri.  I was pretty upset, I mean this had worked flawlessly 20 hours prior.

Then I remembered that even though I had added a keychain camera to the front of my tri yesterday, it's battery had been dead and I wasn't able to use it.  I recharged it before my outing today.  Could this little thing have caused such a big problem?

Innocuous looking little thing, eh?  Well it's evil.  I took it off and bingo, I flew just fine.  It was mounted probably 8cm in front of and below the front of the APM2, but caused a lot of grief.  Later I looked at the flight logs.  Here's where it thought I was flying:

Nice little jaunt over the Atlantic and France, and wow, high-earth orbit!  The camera obviously has RF or magnetic issues with the FC.  Or the FC is über sensitive to noise.

I'm kind of nervous what will happen when I mount my GoPro.

So then I flew happily for a bit.  I've been having issues with my yaw - not debilitating, just irritating.  And enough to prevent any decent AP.  So I tried to get a video of the problem.  Here it is, not good because it was a bit breezy and I was trying to fly while holding the camera, but you'll get the idea.  In the video I try to make 3 different small clock-wise yaw rotations.  Watch the rear motor on the servo, it's all over the place.

If anybody's working on the yaw problem, maybe this will help.

So after flying 5 4S batteries (17-18 minutes each!!!!) I was out of 4Ss and switched to a 3s.  I took it up, checked out stab mode, then switched to alt hold.  IMMEDIATELY all 3 motors shut off and I crashed about 20 meters.  When it hit the ground the 1 motor came back on again and started tearing itself up. I did some major damage to my tri and won't be flying it again for a while.

Has anyone else experienced anything like this?  I really don't want to blame the FC when there are so many things I can do wrong.  But the fact that all 3 motors went out at the same time makes me believe it's not a motor or ESC issue.  When it hit the ground the lights on the APM2 were on and one motor started spinning so I don't think it was a battery connection issue (and the connection was good and tight).  I'm not sure what else that leaves.  And no, unfortunately there was no log file saved from that.  I checked right away and that last flight didn't seem to get written properly to the onboard uSD card (at least I couldn't see it , and my laptop with the 3DR radio had run out of juice an hour before.

I really want to fly this combo again. But now I'm gun-shy.  If this had come down on somebody it would have been bad news.  And I really hate rebuilding.

• ▶ Reply

Permalink Reply by Glenn M on June 22, 2012 at 12:15am

Hi Bruce, you're running pretty much the same setup as me. I'm pretty sure your alt hold crash would have been caused by your throttle trim getting automatically set to a value, say 450 when you were running your 4s batteries. When you switched to 3s (assuming you ran the same props), the trim throttle value would have been much lower than the throttle needed to hover with a 3s battery, making the props spin slower, and making it drop quickly.

As for your yaw issue, I found that having a yaw_rate_p too high would cause the tail servo to move erratically like that. Have you tried tuning it with ch6? I actually ended up ditching that yaw mechanism completely in favour of the rcexplorer.se tricopter 2.5 design and it is much more robust. The delrin one kept breaking bits in small crashes, and it seemed to amplify any wobble in the shaft of the servo.

What props are those?

• ▶ Reply

Permalink Reply by Bruce Jones on June 22, 2012 at 12:31am

Hey Glenn - thanks for the very helpful info.

That makes sense about the throttle trim being reset.  Though it's pretty disconcerting as well.  How should I have reset it?  I would have thought the power-down and power-up would have reset things like that properly.

I've been playing with the yaw_rate_p a bit manually, but really don't like throwing darts at a target I don't understand.  That's a great idea to try tuning it with ch6, when I get back in the air I'll give that a try.

And yeah, I spent some time tonight looking at David's new yaw mechanism and trying to figure out how I can mount the motors I have on one of those.  I like these motors a lot. And of course I had to make my obligatory daily HobbyKing order for a few of those hinges he used.  I may just build a tri from scratch myself starting with David's ideas and going from there.

This afternoon I was using Gemfan non-carbon props.  Yesterday and today I was experimenting with a 4 different types of 9x4.7 props.  The Gemfans flew nicely but were horribly unbalanced.  The Gemfan carbons sounded very nice but again were pretty badly unbalanced.  The Groupners were sweet, but pricey.  The APCs were a bit off-balance, but affordable.  I wish APCs came in different colors.  I tried spray painting them but that seems to weaken them.

• ▶ Reply

Permalink Reply by James on June 22, 2012 at 1:42am

Bruce, 

the throttle trim between 4S and 3S is always going to be different, the only way to set a new trim is to maintain a hover in STAB for a while and it will learn the new setting.

however, in v2.6 i have been having problems with this, as a lot of the time it seems to set a trim value thats way too low.  for now im just very wary as i switch to loiter and ready to switch back to manual control before it falls out of the sky.

i dont really know anything about Tris, but i would suggest that RATE YAW is too fast for the STAB YAW value, making it overtake the desired heading and then rebound back, Dave might be able to help with the right values there.

james

• ▶ Reply

Permalink Reply by Bruce Jones on June 22, 2012 at 2:00am

OK, this is all very good to know.

It sounds like if I stick to the same batteries, I won't have anything to worry about - true?

I'd rather not slow my YAW rate down any.  In fact, I'd kind of like to speed it up.  It doesn't spin as fast as I'd expect when I do a full yaw with the controls.  It's kind of weird in that way - it's like there's only one speed, regardless of how much yaw I give it.  I've kind of wondered if that's a fact of life with the servo controlled tail.

• ▶ Reply

• ‹ Previous
• 1
• …
• 32
• 33
• 34
• 35
• 36
• …
• 68
• Next ›
• Page