GPS no FIX (Solved)


First of all I am electronic engineer and I almost loose my hair trying to solve the no fix with my GPS.


Hardware: APM2.6

SOFT. arducopter 3.01

GPS: 3dr Ublox with compass


hexacopter with T-motor

6 ESC 45 Amp with 3A 5V Bec

Carbon fiber frame

two axis gimbal

Energy system:

2 8000mAh 6s

1 step down 3A 5V (to feed APM via input rail)


1. everytime I start JUST apm via USB I got fix at 1min max with up to 8 sats.

2. If I started APM+ESC+motors no fix at all even been outside with no trees or bulidings direct LOS to the sky.

Tryed Solutions (taken from DIY forums):

1. possible lack of power causing brownout (discarded because of 3A step down, enough power)

2. Connect input via output rail, and then connect the JP1 (didn't work at all, still no fix)

3. Use step down to 18 V, then use APM to power module to filter noise (didn't work at all, still no fix)

4. use toroid in every signal and power line to the GPS and ESC (didn't work at all, still no fix)

5. use external battery to power just apm (didn't work at all, still no fix)

Real solution in my case:

after a lot of nightmare nigths and 300 hairs less this solve my problem.

1. disconnect every ESC

2. Connect one ESC turn on just APM via USB, wait until you get 8 sats, then connect ESC and connect the signal line to APM check if the GPS fix is still valid.

3. disconnect power input, and connect the next ESC.

3. Do it sequentialy not just one by one, I mean first one then two, three.. so on, this helps to see if the problem is electromagnetic, if you just connect one by one individually you won't generate enought field.

4. You will notice that after you connect a faulty ESC you'll loose al SATS inmediatly.

5. change ESC, problem solved.


1. my faulty ESC did have all the normal functios, the BEC was still working and the motor still spin perfectly, I think it was an emi problem from the inner electronics generating too high noise into the power lines.

2. this was my problem solution and I don't want to discard all the possible solutions I mention first, however try first the one that really help me.

Hope this help you.

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  • 3D Robotics

    That's one of the reasons we recommend that people use the 3DR Power Module that comes with APM. It avoids all these issues with flaky ESCs/BECs.

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