We've had some reports of poor GPS accuracy in 2.9.1 as compared to 2.8.1.  This discussion is to debate, test, conclude and if necessary fix issues related to GPS accuracy in 2.9.1.

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Garrick,

    That is some great analysis you did.  Very nice to see that level of detail paid to a problem and getting to a solution!  hat's off to you.

i have spoken with UBlox support regarding this early this year.

http://www.diydrones.com/forum/topics/ac-2-9-1-vs-2-8-1-gps-accurac...

 

 

Garrick, independently of you I have also tried "Pedestrian" mode in my GPS unit (uBlox) and I do confirm, it works significantly better in this mode for my quad purpose.

But you describe also 1/2 wave lenght shield as a second step. Could you share with us exact dimensions of your shield, to not reinvent wheel? 10dB, you mentined, sounds very promising to me! 

Question asked and self answered - so deleted ....

Cheers Kraut Rob

The shield we made consists of simply a copper PC board.  I've found similar material in a variety of places, here's an example on Amazon.  The size of the shield was based on the wavelength of the GPS signal.  Civil GPS receivers use the L1 frequency with 1575.42MHz, which works out to a 19.05cm wavelength.  In the interest of keeping the shield fairly compact, we chose to make our shield half that size.  So I cut the circuit board to about 9.5cm square.  I then drilled holes for the 4 plastic screws to go through that match up with the fiberglass plate the GPS module was zip tied to.  You don't want to mount the GPS module directly to the copper as it will cause shorts.  I also notched the corners to match the notches on the GPS module's antenna as well as to make it less of a sharp object for my fingers sake.  The final step was soldering as short a wire as possible from the copper sheet to the pad on the top of the GPS module labeled "GND".

Why do you need to "ground" the cooper sheet to GPS GND?

My understanding is that cooper sheet is like a reflecting mirror which help the gps signal to be more consistent (concentrate) into the antenna. This means aluminum should work in similar condition. I would try us use aluminum foil for this purpose. I agree we need to avoid direct contact with GPS PCB to avoid shorts.

Actually i am using a ublox variant that has an eeprom but thats another story. I know that the ublox datarate will eventually drop, depending on the configuration (ufo hans/arm-o-copter did some work on that subject, he saw a drop down to 2,5Hz depending on ublox configuration). But that is not a real problem because gps data are received with a timestamp so the controller knows the actual Hz and can act accordingly. I don't see a real problem there. If the gps data are missing, the navigation should simply stop and copter should level (and drift). As simple as that. GPS is always optional and NEVER a thing to desperately rely on. In my country only flying in the line of sight is allowed, so it's nice to have a working GPS but if not, who cares, just fly like always. And in case of emergency/unsure flightsituation turn on the mag (+baro) mode and pull back the stick..... Advertising ANY Flightcontrol as crashfree and could be flown by kids inside a geofence is pure marketing talk that seems to be neccessary in an uninformed society :) .

Cheers Kraut Rob

"GPS is always optional and NEVER a thing to desperately rely on... it's nice to have a working GPS but if not, who cares, just fly like always"

Now my question is: is any reason to buy >2 times more expensive GPS (uBlox), instead of MediaTek?

And last question: Why MediaTek GPS under 2.9.1x and 3.0 is less perform comparing to 2.8.1? Can someone explain this?

Thanks for clarification, Garrick. I have piece of copper board in my drawer, so Im going to tryout your shield.

Another question is - If I set some parameters in GPS uBlox unit via U-center (for example pedestrian mode), is there any way how to protect it against to be that overwriten by APM firmware? Im not sure, if (and if so, when), APM firmware is overwriting GPS unit configuration, are you?

Because Ublox are dirt cheap and way better than mtk. http://www.hobbyking.com/hobbyking/store/__31135__NEO_6M_GPS_Module.... Even with usb and TTL serial for the FC it is cheaper than you think: http://www.ebay.de/itm/271176495992 ...... end of story here.......

If you are unhappy with the drifting around with the mediatek as I was, get the ublox and you will not be disappointed. My quad now drifts less than a meter and I no longer am struggling and spending time and effort trying to make the mediatek better. It is more expensive, but well worth cost.

Haha, somebody had to say it! :)

Seriously though, people must remember that quads can be used for more than just hovering.  And I don't even hold the speed record.  I think it's DaveC.  He had one doing some ungodly speed like 40 m/s?

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