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Old Oct 10, 2012, 08:34 PM
Some call me the other guy!
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Milwaukie , Oregon
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should be fine if it is on, check the gui.
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Old Oct 11, 2012, 12:27 AM
Youtube Johnbrum26
Mckinney,TX
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Quote:
Originally Posted by flyandi View Post
ACC = Level, right?

LEVEL and MAG are both always on and perfect calibrated ...

GPS-HOLD is activated via switch.

So to the GPS' defense .. it was a bit windy .. probably like 2-3mph.
I have mine mag, baro and level on. It will drift alittle, its gps. Also did you set the magnetic declination? In the sketch. The wind will also not help, but it should return to its position not drift off into space.

Which gps are you using?
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Old Oct 11, 2012, 12:53 AM
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San Marcos, CA
Joined Aug 2009
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I am using LocoSys LS20031 -10Hz update rate.

Don't have the baro active. I had some bad first flights where it tried to shoot into the air :-)

Edit: Btw, yeah I set the magnetic declination ... 0.35f based on my location.. could be wrong .. I followed the code instructions:

degree+Minutes * (1/60) and added the "f".

So I went to http://magnetic-declination.com/ and search for my city which is San Marcos, CA:
Magnetic declination: 12 9' EAST
Declination is POSITIVE

= 12+9*(1/60) = 0.35f

--

Now here is something interesting. I went to the NOAA site http://www.ngdc.noaa.gov/geomag-web/#declination

They say that my magnetic declination currently is 12 4' E which would be a value of 0.26f - which is a pretty big difference.. maybe that's the reason?

Latitude: 33 7' 19" N
Longitude: 117 9' 22" W
Date Declination (+ E | - W)
2012-10-10 12 4' 54" changing by -5.5' per year
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Last edited by flyandi; Oct 11, 2012 at 01:41 AM.
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Old Oct 11, 2012, 03:52 PM
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Declination should not affect position hold. What it reads when you set it should be where it stays. You may have something interfering with your satellite reception. As the number of satellites changes, your position is more or less accurate over time.

When you start the GPS thinks you are at x,y and z coordinates. If more satellites come into view and the circle of accuracy gets smaller the craft will seek that same spot again according to what it thought was it's original position. This will look like drift but the gps is just doing what it's told. What is changing is that accuracy of the gps.
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Old Oct 11, 2012, 04:26 PM
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San Marcos, CA
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That makes sense .. I had some trees and buildings around me - maybe they blocked the RF to the GPS .. happened before :-) ... once it stops raining here in SoCal - I will try again in a more open area. (and report back)

Thanks!

EDIT:

One more question: How does it save the coordinates - on arm? Or every time it goes under a certain speed?
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Old Oct 11, 2012, 05:21 PM
Seattle, WA - USA
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Quote:
Originally Posted by Atown93 View Post
Declination should not affect position hold. What it reads when you set it should be where it stays. You may have something interfering with your satellite reception. As the number of satellites changes, your position is more or less accurate over time.

When you start the GPS thinks you are at x,y and z coordinates. If more satellites come into view and the circle of accuracy gets smaller the craft will seek that same spot again according to what it thought was it's original position. This will look like drift but the gps is just doing what it's told. What is changing is that accuracy of the gps.
+1 Good explanation!
An example to show this, look at a map app on a smartphone with GPS. You can watch your position accuracy change over time for the same reason.

What can be affected by a wrong declination is your rotaional (yaw) position during course lock (if you have that function).
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Old Oct 11, 2012, 05:58 PM
'FPV'er...not a "LOS'er
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Las Vegas, NV
Joined Sep 2003
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Quote:
Originally Posted by flyandi View Post
Yeah I had the same thought but I still have access to the USB for emergency and a BT Module for config via phone .. I also can easily access the i2c bus since I made some connectors that I can pull out and connect.. so should be good :-)

Just tested GPS-Hold - although I could see that it was trying to move .. it didn't do it right :-) hehe ...

My understanding is that once activated, it saves the current position and try's to stay in that place ... is that correct?
Andy, let me now when you get the GPS stuff figured out. I've got a RCTimer Nav board and GPS that I want to connect to a Multiwii...just need to figure out what items in the sketch to enable, etc...
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Old Oct 11, 2012, 06:02 PM
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San Marcos, CA
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The GPS is already connected and works .. just pos-hold is not accurate yet.. Going to test tonight :-)
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Old Oct 11, 2012, 06:17 PM
Some call me the other guy!
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Milwaukie , Oregon
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VPAOA, Founding Member.
What this?
Where do we find out more!
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Old Oct 11, 2012, 11:37 PM
"Every boy has a dream to fly"
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Fort Collins Colorado
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DJI Spyderquad: Longboarding (0 min 48 sec)

lovin quadrino and spyderquad
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Old Oct 12, 2012, 02:18 AM
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San Marcos, CA
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So my GoPro got bricked after the last firmware update.. Just sent it in for service.. sux!
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Old Oct 12, 2012, 03:33 AM
Some call me the other guy!
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Milwaukie , Oregon
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How?
Should I be worried?
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Old Oct 12, 2012, 04:44 AM
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UK, North Yorkshire, Whitby
Joined May 2010
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Quote:
Originally Posted by flyandi View Post
I am using LocoSys LS20031 -10Hz update rate.

Don't have the baro active. I had some bad first flights where it tried to shoot into the air :-)

Edit: Btw, yeah I set the magnetic declination ... 0.35f based on my location.. could be wrong .. I followed the code instructions:

degree+Minutes * (1/60) and added the "f".

So I went to http://magnetic-declination.com/ and search for my city which is San Marcos, CA:
Magnetic declination: 12 9' EAST
Declination is POSITIVE

= 12+9*(1/60) = 0.35f

--

Now here is something interesting. I went to the NOAA site http://www.ngdc.noaa.gov/geomag-web/#declination

They say that my magnetic declination currently is 12 4' E which would be a value of 0.26f - which is a pretty big difference.. maybe that's the reason?

Latitude: 33 7' 19" N
Longitude: 117 9' 22" W
Date Declination (+ E | - W)
2012-10-10 12 4' 54" changing by -5.5' per year
Hi,
I am sure that some one will have pointed out the error in your method. Just in case they have not here goes. When you enter declination you enter it in degrees, entered as a float, thats a kind of number used by C++ and other computer languages. In order to convert THE MINUTES part of the number you divide the minutes by 60 as there are 60 min per degree. This expresses the minutes in the decimal format. The formulae should read in your case

12 degrees + (9minutes / 60) = 12+0.15 = 12.15f
If you already sused this OK, some others may have missed the point.
A latter contribute r was right the declination will not effect the ability of the GPS to hold position but it will effect the accuracy of that position.

Regards

John
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Old Oct 12, 2012, 10:34 AM
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This brings up a good point. And it happens to be something guru talked about in our webex on Sunday.

The difference between accuracy and precision in relation to using a GPS.

I'll make an effort here to share what I know for the edification of anyone considering using a GPS or perhaps wondering what they can or can't do with the unit they may already have.

Precision is the ability of a sensor to detect it's current state..... nothing more. The precision of a GPS depends not just on how many satellites but also where they are in relation to each other. For non military sensors about a three foot radius is about at accurate as you can get. That is also dependent on the sensor and even things like space weather will affect accuracy. I won't go in to military accuracy as it's a bit scary.... A three foot radius is pretty big for a quad so those who expect to be able to lock their craft to an exact point in space and not have it "wonder " a few feet may be frustrated to find that it can't be done consistently.

Accuracy on a GPS is it's ability to not only know where it is in relation to the satellites it's tracking but also where it is in relation to the earth's surface. This is where your magnetic declination comes into play. In order to accurately plot a course you need to know where you start from and where you are in route. Without getting in to the difference between magnetic north and true north, declination is essentially how far you are from one of our magnetic poles. This is then used to accurately figure where you are.

Because multiwii has no "mission planner " yet, accuracy and your declination really are not in play. Once those features are added, declination will be important. Note also that keeping your declination up to date is also important as the magnetic poles shift over time.

If you want position hold and rth, precision is what your after.

If you want to use some sort of auto pilot feature to go somewhere specific, accuracy is what your after.

Hope this helps.
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Old Oct 12, 2012, 10:51 AM
Registered User
San Marcos, CA
Joined Aug 2009
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Ahh... I used the formula that they put in the code and misread it :-( .. Thanks John for pointing out that mistake.
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