Replies to This Discussion

Permalink Reply by Matt Gaige on April 14, 2012 at 7:46pm

I would never fly this way in acro / manual mode, but in Stabilize mode it is great.  I also saw more issues uncovered, air causing vibtations.  Again this was for slower Photography flying.

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Permalink Reply by John Campen on April 14, 2012 at 6:51pm

Barometer Issues!?. 

Ok, here is another problem Ive spotted in the mind field of hardware issues and for people who continually bang their heads trying to fix them through PID tuning. .

If you have a housing that is covering over all of your electronics such as a plastic container,.. then when you descend or ascend quickly the pressure inside the container changes and gives your barometer an false reading.  

For example if you descend quickly the pressure increases inside the container making the barometer think that you are descending faster than you actually are. So the APM will try to compensate this out and try to increase the throttle and this probably cause a bouncing behavior some people are finding happens .

Some may argue that the barometer cant be this sensitive, but I beg to differ because the pressure variation it can sense for the pressure variances in altitude that it works off is very fine. The pressure change inside the container even for horizontal flight will be enough to for it to sense the changes of pressure in the container.

This also includes pressure zones around the incoming and out going air stream around the props if they are to close to the container or even if you have an open center frame the pressure zone around the props can possibly still affect the barometer

Im considering some fixes for this such as a tube that has a H tube branch at its end and that sits above or below the center board.

I would be interested to know what others view and ideas are on this. .

Ive opened a separate discussion on this here  http://diydrones.com/forum/topics/barometer-issues-and-pid-tuning

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Permalink Reply by Allen Bishop on April 15, 2012 at 8:40am

I found the same issue about six months ago.  I use a clear plastic light post dome that I cut in half for my Quads.  I have since drilled 1/2 inch holes  around the top of the dome.  This allows air to vacate when decending and to allow pressure equalization on rapid assents.  Here is a picture:

There are six 1/2" holes around the top.  Sorry, they are hard to see in this photo.  This works really well and since the dome is cosmetic only (I don't fly in the rain) it actually looks good with the holes.

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Permalink Reply by John Campen on April 16, 2012 at 7:51am

Looks nice Allen. I only have the cover to protect the electronics when i crash. I started a post on the below link and have some ideas about testing and reducing the pressure anomalies. Nice to know then what I suspected has happens to others as well and something to keep an eye on when we see strange behavior

http://diydrones.com/forum/topics/barometer-issues-and-pid-tuning

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Permalink Reply by yovio on April 14, 2012 at 11:03pm

Hi,

 

I had try ttuning Loiter in 2.6 beta, still no luck, the quad will stay for about 5 seconds after that it will fly away for upto 25 meter before I stop the movement by taking the control back. My quad using X525 frame with NTM motor 2836/750 KV. Stability mode fly perfectlly stable and no issue with compass.

I wish someone can help me analyze my log and give me some hint on which parameter I should tune. I have enable PID logging, and in these flight I use Chanel 6 tuning to tune LOITER_P values, min = 0 to max 1500.

 

I had 2 flights and both of them no success in Loiter.

 

Thanks

Yovi

Attachments:

• 2012-04-15 13-39 2.log, 594 KB
• 2012-04-15 13-40 3.log, 463 KB
• X525(initial loiter)-2.param, 3 KB

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DeveloperPermalink Reply by Randy on April 15, 2012 at 1:11am

Yovi,

     Thanks for the logs.  You were tuning the loiter speed which controls how quickly the copter wants to get back to the target.  What's more important is to tune the loiter rate which controls how much the copter leans to achieve a given speed.  You can see this in the pic below which is the latest mission planner.  Your loiter rate's P value is 0.6 but the default is 2.0.  It looks like it needs to be quite a bit higher than 0.6 so maybe try tuning it starting with a value around 2.0.

     The reason I think 0.6 is too low is that although we don't have the exact output from the inner loiter rate controller, the NTUN (navigation tuning) message has two column, "nav lon I" and "nav lat I" which show the "I" term on this inner controller. In the pic below you can see this I term keeps climbing and eventually builds up enough to bring the copter back but it takes a while.  Much better to increase the P term.

      In the pic below, red and green lines are how far the lat and lon are from the target.  The blue and white lines show the I term build-up on the loiter rate controller.

    Hope this is clear-ish.

-Randy

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Permalink Reply by Eric Tweet on April 15, 2012 at 2:00am

Randy,

I appreciate this explanation. I'm in the same boat as far as nailing down the tuning, so this helps me as well. What do you think we should expect if we instead tune the loiter Rate P value too High? Would it lean heavily and rapidly overshoot back and forth across the target location?

Also, do you have a suggested starting value for a standard 3DR quad with 880kv and 12x4.5 props? 

Thanks for the help!

Eric

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DeveloperPermalink Reply by Randy on April 16, 2012 at 7:19am

Eric,

     Yes, if the Loiter Rate P is too high it will lean too much.  I've never tried cranking it up far too high but I guess it would lean too far forward and then too far back back repeatedly as it approaches the target.  And then once it gets there it would have a hard time staying there.

     There are probably many ways to get overshoot but one way that you will get that is if your Loiter Rate P is too low.  What happens in this case is that the I term builds up as you're approaching the target but then because the I term reacts slowly, it will stay high as you sail past the target.

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Permalink Reply by yovio on April 16, 2012 at 7:38am

Hi Randy,

I just went back from another test, this time I tune LOITER_RATE_I using CH 6.

The result, copter stays within 10 meters box, I'm not satisfy yet.

As a brief, bellow are some values on the parameter (Full parameter attached):

LOITER_RATE_P = 2.68

LOITER_RATE_I = 0.010 (This is my starting point, CH6 configure to tune this from 0 to 1.000)

I've tried to analyzed my logs and according to my understanding my LOITER_RATE_P is too high.

I will try another test tomorrow, my plan for tomorrow is:

I'm gonna set LOITER_RATE_I to 0.2 and I will use CH6 to tune LOITER_RATE_P.

If you have other suggestion please let me know.

I'm really appreciate all your input.

Thanks

 

Yovi

Attachments:

• 2012-04-16 21-46 6.log, 740 KB
• Parameter use during today's test.param, 3 KB
• Parameter will be used for tomorrow test.param, 3 KB

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DeveloperPermalink Reply by Randy on April 17, 2012 at 7:09am

Yovio,

     I think you're right actually, I think your loiter-rate P is a bit too high.  The little jagged edges in the P component (green line) are quite visible and of course this carries through to the output (white).  I know I'm going back on my previous advice a bit but I think you need to reduce both the loiter rate P and maybe the Loiter Speed a bit.

 

     As a side point, at some point I'd like to try testing the output of our controller at various speeds.  So for example, set up a case where it tries to maintain various speeds one after the other (i.e. 0.5m/s, 1m/s, 1.5m/s, 2m/s) so we can get a better idea of how good it is in varying situations.

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Permalink Reply by yovio on April 17, 2012 at 8:13am

Hi Randy,

Here is another test, this time I reduce the LOITER_SPEED to 0.4 and LOITER_Rate_P to 1.9 and play with RATE_I, still not satisfy, I guess this time my Rate_P is too low and somehow when error reached 0, the I still too high and it make oscilation.

It is so dificult as I don;t have telemetry nor laptop to tune the parameter. I guess I need to find a way to power up my laptop on the field (The battery has been damaged).

I think I like LOITER_SPEED 0.4 as it seems the quad is more faster in correcting the error.

As usual, inputs are highly appreciated.

 

Cheers,

 

Yovi

Attachments:

• 2012-04-17 22-56 4.log, 674 KB
• X525(initial loiter)-4.param, 3 KB
• 2012-04-17 22-55 3.log, 718 KB

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Permalink Reply by Gerrit Jan Baarda on April 15, 2012 at 2:18am

What is the unit of 'Loiter speed' in mission planner? The wiki doesn't seem to mention this in the tuning section.

I'm asking this because I had some succes at tuning loiter in low wind conditions, but so far have come nowhere in windy situations. 

Thanks,

Gerrit Jan

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