Morning all.


My flying buddy and I are trying to finish off our APM build, but are running into a very odd problem, and we are not sure what could be causing it. That is normally a good reason to ask the internet, but I thought I would ask the professionals first!



APM1280 with Oilpan (H) connected to power from the ESC


Problem is:

When connected to the USB, IMUs power up, GPS locks and we are all happy. Telemetry comes through the USB and everything looks good. As soon as the battery is plugged in, or it is started up on the battery, GPS drops off line, telemetry reports no GPS and only the IMU/Gyro/etc work.


The software tester in me thinks that we have a power problem, and feeding the APM through the receiver is probably not a good idea, but that a separate 2s LiPo providing dedicated power is. I have _never_ seen the GPS drop off-line in testing on the bench before and it is only when in the airframe that we see this problem (i.e. not on USB power only)


Any ideas welcome, and suggestions gratefully received.


Yours aye,




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Read this discussion, it might be helpful. Same symptoms. But it is not a lock as a solution, just something to check quickly.


Long and short of it, try to power up w/o the receiver attached, see if the GPS works. If so, try to attach the RX farther away from the APM, see if the GPS works. Any if so, maybe consider getting a better receiver.

you can skip reading anything I wrote on the thread, just me misleading (as usual) and just read what Eric found.

Receiver is a brand new one bought specifically for purpose (will get the brand/model later), so I am not too confidant of that being the issue. It will get checked though. Also, the two are quite well separated. I'll check the exact distance, but they are hardly touching.


Maybe one of those Alu APM boxes is required...

The receiver is a graupner R16Scan, and it's quite far from the APM. Will try without it, but manual flying might be a bit difficult ;) I will also try a diffrent powersupply for RC rail and the APM, just in case. 


lol. yeah, I only mean to try w/o rx on the bench, for testing and diagnosis :)

Apparently we've sorted out this problem. Well i've found the possible source of the problem. It is not the radio, but i've moved it farther from the APM. If it's powered vi the ESC : no GPS fix, if it's powered by any other mean : i got GPS fix. So i've added a 5V supply in the plane to power the RC bus and the APM and it works fine hopefully.


The ESC is a turnigy TRUST 55Amps SBEC but i don't know what's wrong with its supply (should find an osciloscope to look at the power... ) link : 

False alert : problem is not sorted out !!!! :)


Here's a quick update on the tests and the findings : 

  • USB connected, APM powered via RC rail by 4AA batteries, no ESC attached : GPS blinking blue, LED B steady and C blinking (red)
  • USB disconnected, APM powered via RC rail by 4AA batteries, no ESC attached : GPS blinking blue, LED B steady, NO activity on LED C


In all cases the receiver is on and wheteher it is close or far it is the same behavior (falsely accused so far).When i say USB connected i mean USB cable physically connected. It is the same behaviour whenever i have Mission Planner connected or not at software level. I've done a APM reinit (reinstall software, reparameter everything).


Any ideas of the possible cause of the problems ?  

more infos : 

  • USB connected : measured 5.5V on the GPS breakout board.
  • USB disconnected : measured 5.2V on the GPS breakout board.


  • 3.3V shows 3.15 al the time with or without USB power....

Another bit of information : 


I've decoupled the RC Rail power from the APM, and powered it with a 2S lipo battery. It works fine then (red led and GPS fix). It also fixes my  stabilization problem (all channels went to 1500 when asked to stabilize). So i'll go for a field test as soon as the wind goes down.

But the real quesiton remains : what is the source of this problem !!! :)

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