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I have two VR cards:

One VR Brain 4.5 with uBlox 6 (3DR GPS) flying an Hexa and one µBrain with uBlox 8 on a smaller Quad.

I upgraded both to latest rc10 version. VR Brain 4.5 is OK (also with EKF) but µBrain GPS performance is poor. Compass calibration is fine. Included is the latest flight log with GPS errors. I had a look at the GPS prediction yesterday and checked the GPS reception with µBrain: it is like there is no GLONASS acquisition.



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Hi Marc! I am having the same problem with my VR GPS M8N and VR μBrain, I have a constant drift to the right but not sure of the problem.

Would you be so kind as to send me the results of his compass calibration?

Offset x =?

Offset y =?

Offset y =?

I want to compare their data with mine to make a comparison.

Offset x = -86

Offset y = -39

Offset y = -7

I did a manual calibration (rotate the copter manually when hooked to computer via USB), 

Do not forget Compass_dec

I didn't perform compassmot calibration



Thanks Marc, I have done the calibration process more than 30 times and have not been able to achieve these results.

My results are:

Offset x = -78

Offset y = -7

Offset y = 68

Marc, please specify the Board with the u-blox NEO 8 (M8N ?) you are using. Or we will start to call the Brains just ARM 32 F4, which is only part of the story. I personally own 4 different GPS boards with NEO M8N , one with MAX M8Q, there are probably a lot more designs available. If you own a Reyax825AI, we don´t need to guess whats wrong...All of them you can configure and check via FTDI and u-center (config view), that goes for the GNSS settings as well. Enable GLONASS and GPS, disable BEIDOU and QZSS and save the settings. If GLONASS isn´t set, you should as well check the other settings as well, My proposals are:  airborne 4G, ubx out, 38.400,5Hz and SBAS set to EGNOS if you are located in Europe. Although AC is supposed to write these settings itself (if RX pin is properly connected) onto the chipset @ each boot, that might help your understanding.

If its an VR GNSS board with NEO M8N , Roberto or Emile (?) might want to provide a complete setting text (ubx txt), his devs created for proper function. Don´t use the ubx txt created for 3DR LEA-6H (V1.1,V1.2)

PS: I saw some minicopter setups with GPS/GNSS located very low (within copters own interference field), close by "GPS jammers" such as GoPro or even worse Mobius CAM, FPV antennas and telemetry tx...,

All these nearby installed and turned on devices lead to poor reception as well...which is a serious issue with mountings shown here as well... If so, turn of these gadgets, put the GPS onto a Mast and you´ll most probably notice better results.

Hello Gervais,

My NEO 8 is from Virtual Robotix. VR GPS NEO 1.1 (TAOGLASS CGGP.25.4.A.02). I got it with the µBrain. I checked logs from earlier version firmware and I have some logs with 15 sats and a small Hdop.

I have to made an adapter for my FTDI before using u-center. I saw the wiring somewhere (had to find it again).




Hi Marc,

about the VR GPS 8 is important that your gps is far 10-12 cm respect of esc and fly controll in our test you found a iusse about the RF noise from the esc or from the cpu inside the flight controller.

The main difference respect of standard UBLOX LEA module is that the antenna filter is not selective as the LEA because need to recived signal  from GPS , Glonass and Galileo ,too.

So is very important to reduce as lot as possible the rf noise ... try only to put the gps more far respect of actual position and check if so you recived more sattelite .

Normal that is main problem that we found on Multi constellation GNSS.



Hi Roberto,

I moved my Bec and I now have a shield between µBrain and GPS. GPS 3D acquisition is more swift but I stay with 7 to 8 satellites when I should have around 14 or 15 when including Glonass constellation. 

I had a try with u-center, without success, Red GPS Led is OK but no apparent communication with the card (green icon is not blinking...). There is no Rx-Tx activity led lighting on the FDTI adapter. I try GND/Rx/Tx/5v pads on the GPS card, no success, I also try with a plug in the GPS plug (+/-, Rx and Tx)...

Another recurrent problem with the µBrain, when I try to upload firmware via APM Mission planner, µBrain hang during HexFile reading, hang also when trying to reconnect after unplug/plug procedure. (Hang=Led stay -no blink).

It also hang randomly when booting (from USB or from battery)


About the GPS and Ublox you cannot see any data until you set the GPS as default .... 

at that point the GPS switch to 9600 and the NMEA is active .

If you want to restore a good comunication parameter you need to set the speed at 38400 and deactivate the NMEA on uoutput port mantain only Ublox binary format. 

14-15 satellite is not so bad ... normally i fly with all constellation GPS+ GLONASS with 13-17 satellite available . In special static situation where GPS stay on for long time i see until 20 satellite and 0.7 as hdop ... normally is near 1.6 - 1.0 depend respect at status of constellation .

The Hang could be depend of low current available on your usb port .. how often happen ? 



For the µBrain problem, USB voltage is 4,4 volt,

Bec voltage is 5,1.

It happen often. Even when card is powered by Bec and I try to perform firmware update from APM. Hang always when trying to reconnect (blue light) after Unplug USB, Click OK, Replug USB. Hang sometimes when reading Hex file (from internet?).

Hang sometimes at boot from Bec,

GPS set to default procédure: is there a switch or short to do or is it from u-center menu?



There is no need to set it to DEFAULT (which will erase presets) to see data. Just click on DEBUG MESSAGES (2nd row, 4th (last) button @ u-center 8.11)

Problem is solved with the help of Roberto via TeamViewer session. GPS was OK but wiring around it may be too noisy. I removed some wiring clutter and moved the GPS away from the µBrain.

To be tested in flight,



Hello Marc,

Did you get good results with your flights with your M8N GPS ?





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