Replies to This Discussion

DeveloperPermalink Reply by Randy on July 27, 2012 at 6:28pm

Kur,

     Ok, the video is very helpful.  The increase in engines is just because your quad is trying to adjust the way it's facing.  What you're seeing is the ramp up in I term for the yaw controller.  In fact, it's likely only increasing the speed of two motors, and decreasing the speed of the other two.

     Notice how the motors slow back down again once the quad breaks free and manages to turn a bit?

     So I think there's likely something wrong with your compass (maybe your offsets have gone crazy).  Could you connect with the mission planner and look at the flight data screen and make sure that your heading is stable and not constantly turning?

-Randy

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Permalink Reply by Kur on July 27, 2012 at 7:38pm

Randy,

Heading looks stable but in the flight data under Quick Tab. Alt, groundspeed, wp dist and verticalspeed are keep changing (I am not touching the quad at all. Its sitting still on the table. Of course without props). Yaw seems to be little steady (Jumps couple of points sometime).

Kur

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DeveloperPermalink Reply by Randy on July 27, 2012 at 8:15pm

Alt changing may be normal because the barometer has a "random walk" behaviour..meaning that it drifts up and down around the actual altitude.  Throttle control is completely done by the pilot in stabilize mode so the APM2 won't try and adjust the basic throttle value based on this in any case.

 

I'm sure it's yaw related.  In fact I'll bet you can temporarily make the problem go away by setting your stabilize Yaw I value to zero.  This isn't a perfect solution though.

Sorry to keep asking you to try different things but could you take your props off and try increasing your throttle to see what happens to your heading?

Also can you connect through the mission planner, then go to the Configuration screen, then Parameter List, and tell me what your COMPASS_OFS_X, Y and Z values are?  They should be in the range of +-200..but sometimes they're larger..larger than 300 or 400 is definitely a problem.

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Permalink Reply by Kur on July 27, 2012 at 8:45pm

No thats totally fine. I am really thankful to you for troubleshooting this issue.

Do you wanna me to try increasing the throttle while its connected to Mission Planner? (I believe that's what you meant but just making sure). If yes, then nothing is happening. I tried the max throttle. Quad doesn't move at all (Looking at the Flight Data Screen in the Mission Planner)

I have attached the Parameter file. Please take a look at it for all the values. 

Here are the values for:

COMPASS_OFS_X	-79.849
COMPASS_OFS_Y	51.593
COMPASS_OFS_Z	183.379

Thanks.

Attachments:

• ParametersJuly27.param, 4 KB
• ScreenShot1.png, 42 KB

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DeveloperPermalink Reply by Randy on July 27, 2012 at 9:14pm

Kur,

Those offsets are a-ok. Have you actually tried taking off? I guess you're saying that it tries to flip over...You're sure you've got it in the correct orientation (i.e. + or x) and that your props and motors are turning in the correct direction according to this wiki page?

The slow increase in throttle is because of the yaw I term I'm sure. So just as a test, please try reducing the Stabilize Yaw and Rate I terms to zero and repeat the 1/3 throttle test. I'm sure you'll find that it's not slowly increasing the throttle anymore.  Please remember the values before you erase them though because you'll want to restore them later.

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DeveloperPermalink Reply by Randy on July 28, 2012 at 5:41am

I posted back on the main 2.7 discussion but here it is again..

I think I know what the issue is...I think the IMAX value of the Yaw Rate term is too high (it's 50 when it should probably be around 8 or 10). So what happens is that while you're sitting on the ground, your yaw drifts a little (which is normal) so the yaw controller's I term builds up increasing the power to two motors (and reducing to the other two) in an attempt to cause a rotation but it's unsuccessful because it's on the ground.

I think on earlier versions of the code, we had the Rate Yaw's I Term as zero so it didn't matter about the IMAX but now it does.

Can you reduce the Rate Yaw's IMAX and see if your problem goes away?

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Permalink Reply by Kur on July 28, 2012 at 9:18am

Randy,

Now i am going to quickly update the changes you suggested and try to test it out. Its going to be raining the whole day today. But it stopped right now so i will quickly try it out. I just wanna be safe and don't test it out in side the house.

So just super quick question. Do i have to change both IMAX values of the Yaw Angular Rate Control and the Rate Yaw? I am asking this question because these both numbers are the same. So i am wondering if they should be the same or ? 

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DeveloperPermalink Reply by Randy on July 28, 2012 at 10:03am

Kur,

      We have multiple screens in the MP's configuration area that actually show the same information.  The idea was that very experienced users who know all the parameters want a compact view where they can access all parameters while other people want a view with more information about what each parameter does.  So apologies in advance if I misunderstand your question but I think you can update the value in your screen shot or the one in mine and it will have the same effect.

      By the way, I've checked in a small change to stop the iterm from building up at least when you've got the throttle at zero.  This won't help you until we push out the next release...whether that's soon or not probably depends upon how many other people hit this problem.

-Randy

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Permalink Reply by Kur on July 28, 2012 at 11:47am

Randy,

Oh ok. No, you understood me right. The information is the same (Value of Yaw, Loiter, Pitch, Roll...etc) but they happened to be in multiple menus. Thanks for explaining to me.

Alright, i changed the Yaw IMAX value to 10. I think, it did help a bit but now quad is jumping up & down. I don't know why. I am not giving much throttle (since i am a beginner and don't wanna go crazy). I am trying out just simple things, Forward, Backward, Up, and Right. But as you can see in below videos that quad is jumping up and down by itself. And when i try to bring it little higher  from the ground by giving little extra throttle(so it doesn't hit the ground). It just keeps going higher and higher, and when i lower the throttle it just drops out of no where. (You can see at very last of the video Trail - 4). 

Also, i am hearing some squeaky noise while quad is in the air. I am not sure if its motor or something else. If you listen carefully you will hear the squeaky noise coming out from the quad. 

Here are the video Links:

 

Trial -1

Trail - 2

Trail - 3

Trail - 4

DeveloperPermalink Reply by Randy on July 28, 2012 at 5:57pm

Kur,

     That's looking good actually.  Your Rate and Pitch rate values are a little high for your frame+motors I think which is causing a wobble.  I'd recommend reducing them by 10% ~ 20%.

     Re the bouncing...that's very normal for new pilots.  In stabilize mode, the throttle is almost completely under your control.  So the bouncing is actually because you have the throttle at a good level but your quad is moving in and out of the "ground effect" (the props provide more lift when it's very close to the ground).

     Mostly you'll get use to the throttle control with more practice..but one more question, have you calibrated your ESCs yet?  This may provide you with a better range of motion to control the motors.  At the moment it may be that it's a very fine line between rocketting into the sky and falling to the earth..you'll probably just need to get use to where that point is but calibrating the ESCs might make that fine line a litter fatter.

Permalink Reply by Vernon Barry on July 28, 2012 at 6:11pm

i am hearing some squeaky noise while quad is in the air

If you notice, that noise is in sync with the slight wobble of the entire machine in the air (video 4). That sound is the motors trying to change speed rapidly to stabilize the aircraft. The wobble means your PID values are too tight (too much gain in feedback).

This will cause you problems sinc the motors are constantly reving up and down and add to vertical instability. The question here is what motors and props are you using and battery (3 or 4 cell)?

I think you have over powered motors (that's fine) but if that's the case, then you must lower the P value in yaw significantly. Again, it's obvious in the video you are slamming the heck out of the feedback loop.

 

Basically, whenever you have to much gain in a PID loop (P for Proportional) it just goes into oscilation. That's exactly what's happening.

http://code.google.com/p/arducopter/wiki/AC2_Tweaks

Basic performance troubleshooting

For normal flight, there is really only one term you should care about and that is the Rate Roll P setting (Rate Pitch is normally slaved to that, as the checkbox on the screen above shows). Use the in-flight tuning method with CH6 to nail this term in a few seconds. Make it as aggressive as you can before it begins to oscillate. You will have great performance descending straight down if this term is higher. You may want to tune it down a hair more if you like a softer response.

Here's an example: the default setting for Rate Roll P is 0.14. This is optimized for the standard Jdrones/3DR quadcopter with 850 motors and a 10" prop. If, however, you're using the bigger 880 motors and a 12" prop, which are much more powerful, that Rate Roll P will be too aggressive and your quad will seem quite unstable. So in that case, lower your Rate Roll P to 0.1 or 0.09, and you should see much more stable flight.

The same is true for Altitude hold. Throttle Rate P needs to be adjusted to get optimum altitude performance.

These two terms go a long way to making your copter perform well, and are highly dependent on the thrust to weight ratio of your copter. More thrust = lower gains.

• My copter oscillates slowly (larger movements) when stabilized: Lower your gain in Stabilize Roll P.

• My copter oscillates quickly (smaller movements) when stabilized: Lower your gain in Rate Roll P.

Permalink Reply by Kur on July 28, 2012 at 8:33pm

@Randy. Yes, i have calibrated my ESCs couple of times now. But i will re-calibrate them tomorrow (shouldn't hurt). 

That's looking good actually.  Your Rate and Pitch rate values are a little high for your frame+motors I think which is causing a wobble.  I'd recommend reducing them by 10% ~ 20%

Sorry, but I am little confused here. I am not sure what do you mean, when you say reduce your pitch rate values!? I mean i know where can i find pitch rate values. I am just not sure which one should i reduce. P value, I value, D value or IMAX value? It would be good if you can tell me particular values. I am going to attach a screenshot of all my ArduCopter Config below.

@Vernon. I am using HackerStyle 20-22L with 10*4.5 props and flightmax 4000mAh 20C 3Cell 11.1V battery. 

Thank you so much for that link. I have to read the whole wiki really carefully. Its very informative. As you mentioned that, the default value for the Rate Roll P is 0.14. And it should be reduced if you are using bigger rpm motor or bigger prop or both. Currently on my quad, the default value for the rate roll P is 0.18. I think, that's one of the issue. Since i am using higher rpm motor (924rpm). The value of Rate roll P should be lower than 0.14 (Standard for 850rpm motor)?

And also i wanna ask about the IMAX throttle rate. Currently, i have it as 180. Does it look good or kinda high? Please let me know. Thank you so much for your help.

 

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