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Old Aug 14, 2012, 04:44 PM
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Joined Aug 2012
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Help!
OSD Pro GPS Accuracy

Hello,

I recently purchased three OSD Pro systems for myself and my son. Our main reason for purchasing these systems was the antenna tracking feature. When we set up the first system on my son's helicopter, we noticed that the GPS altitude was very slow to respond and would drift hundreds of feet even when the helicopter was not running (just sitting on the runway). We have set up two of the systems on wooden panels just to see how the GPS altitude and position respond when in an isolated environment. The altitude still drifts from about - 20 feet to +100 feet. Both systems we have tested perform similarly. The lateral position drift is anything from 20 feet to as much as 80 feet. This altitude and position drift is happening with the system mounted on a wooden panel resting on a table outdoors. The system was reporting at least 8 satellites in view, so I'm sure the GPS module is working. I can't see how this performance is suitable for use as an antenna tracking system. What sort of accuracy should be expected from these systems? Is the antenna tracking feature really functional with this level of (in)accuracy from the GPS expander? Any help would be appreciated!
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Old Aug 14, 2012, 06:09 PM
Registered User
Brisbane Australia
Joined Mar 2003
568 Posts
Hi Conan,
I cannot help you but you are not alone.
My Eagle Tree GPS system suffers from a similar level of inaccuracy.

I have tested it out in our back yard and it reports that I am over the other side of the road. Not just the starting point but the whole track is shifted to one side by about 100ft..

When I fly at our club field and the logger reports that I have flown in a no-fly area it is a great concern. I do not want to be disqualified from competitions because of a GPS logging fault.

I hope someone has the solution.
Regards Graeme.
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Old Aug 14, 2012, 06:54 PM
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Joined Aug 2012
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Graeme,

Thanks for posting a reply. Maybe the Eagle Tree rep will chime in and help us understand what is going on. My son talked to him on the phone, but has been waiting nearly two weeks for a call back. This is especially frustrating given that my new DJI Naza with GPS can keep my multirotor in place within about 2 meters. The specs on the Eagle Tree GPS unit claim 2.5 meters of accuracy. None of the three units I have are consistently within 100 feet. To make matters worse, they will display literally hundreds of feet of drift even when they're parked on a table (outdoors). Too bad Eagle tree doesn't offer a better GPS unit. I really like everything else about these systems, but they're useless to me without the antenna tracking.

Regards,

Conan50
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Old Aug 16, 2012, 02:12 AM
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Norway, Hordaland, Bergen
Joined Feb 2009
280 Posts
Hi,

The answer is to use the barometric altimeter.

Because GPS altitude is not very accurate.. And its not just how many satellites (ofcourse more is better) but also the position of the satellites, so two different days with equal no. of satellites can have different altitude accuracy.

I have not checked, but I'm sure the naza has a barometric sensor.
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Old Oct 28, 2012, 05:25 PM
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Anoka, Minnesota
Joined Oct 2008
8 Posts
Hey Conan50,

What ever came about with this post? Did you get an anwser to why the GPS is so far off? I am seeing the same thing.
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Old Nov 02, 2012, 06:54 PM
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Joined Nov 2003
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Hi, can you describe what you are seeing with the GPS, and under what conditions? Also, can you let me know the model # of the GPS, and what equipment you are using with it. Thanks!
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Old Dec 10, 2012, 08:07 PM
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Sacramento CALIF U.S.A
Joined Mar 2001
23 Posts
Gps way off

My gps reports -350 ft or so when im at 29 ft sealvl .ive restarted 3 times the unit will climb to 100 ft when i take off then go 5000 ft then back to -minus whatever. whats the deal ?
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Old Dec 12, 2012, 01:50 PM
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Joined Nov 2003
4,920 Posts
Hi, can you let me know the following:

a) what model of GPS you have, and if it's the V4, does it have the toroid ring in the wire?
b) Are you using an FPV video transmitter? If so, is it very close to the GPS? Goal is to get it as far away as possible.
c) Are you in an area with a lot of obstructions, such as next to a cliff, or surrounded by forest?
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