Help! APM 2.5 output #3 dead

I have no idea what caused this, but my 3rd motor output is dead.
Resoldered, switched leads, and its definitely on the board. Lead goes to pin 17 on the mega, but I doubt I can check it there with a scope without smoke.

Is there a way to patch/reprogram to use one of the unused outputs?
Otherwise am I heading for another APM board?

I see RC_functions for the outputs in the advanced parameters, but don’t know how to switch output 3 to 5 or so.

Way back when Bill Gates was in knickers I could do some good hex patching. Unfortunately I declined the option of learning C.

Any help appreciated.


If you’re ok compiling and uploading the code yourself with our patched version of arduino then you could go into the AP_MotorsQuad.cpp file and add a 5th motor which is the same as the 3rd.

 So say you're using an X frame then add this line below the definition for motor 4..somewhere around line 58.

 Then attach the #3 motor to the 5th output on the APM.

Dev wiki to install the special arduino: … o-windows/

Get the AC3.1 zip from here: … pter-3.1.0

best of luck.


Thanks for the reply!

I assumed it would take this to fix it. Again, I have no idea why it failed.

I compiled the source when I first started in May and was successful.

The new guide from start to finish looks great and I’ll start on a fresh computer and give it a try.

Hopefully it will give me some confidence in my ‘retired’ programming skills and I’ll have some fun.

I just had my first “3 battery day” with no broken props/quad using the latest software! Sonar is dead, but automatic soft landing was fine.


I just logged on to the board to complain about my APM2.5 output #7 going dead. It was fine when I last flew a few weeks ago, and dead yesterday when I went to go for a flight. Whatever motor/ESC combo that I connect to output #7 displays the same symptom… (A Beep every one second with a corresponding motor twitch)…

Did you manage to get your the output working again and if so, what did you do ?

A beep every second usually means, the ESC doesn’t get any valid signal. The motor twitch comes because the ESC doesn’t have a loudspeaker but vibrates the motor to create the beep.

Triple check all the cabling, especially the signal cable from the APM to the ESC.
Plug the ESC signal cable directly into the receiver and see if you can spin the motor up that way
[size=150][color=#FF0000]WARNING: REMOVE PROPELLERS BEFORE DOING THIS TEST![/color][/size]

If the ESC complains that it doesn’t get any valid signal and the cables are all good, it means, either the APM’s firmware is seriously messed up or you somehow managed to fry the corresponding output of the 2560.

You can test that using this method: Link
[size=150][color=#FF0000]WARNING: REMOVE PROPELLERS BEFORE DOING THIS TEST![/color][/size]

If the cabling is good and you can’t get the motors running with the APM, contact 3DR support about if the APM can be repaired.

Thanks for the reply… I should have put more info in my post… I just looked back and see that it was pretty sparse.

I did check the wiring back to the APM. It’s the #7 output that is dead. If I connect any other of my motor/ESC pairs to output #7, they display the same symptom. So it appears there is no signal at the APM pins. I also checked the circuit board with a magnifying glass and can’t seem to find any breaks or damage.

I’ll be contacting 3DR as you suggest…

Now 2 strange APM output failures. ? At least the one with #7 dead has a resale value (for Quadcopters, like mine). :slight_smile:
I’m starting the recompile recommendation with the patch for mine.
Learning programming (again was on my To do list for sure.

Randy’s patch worked great! The guides on git & installation of Arduino, etc was awesome.
Now to enable the crop dusting portion! I do plan to drop watet balloons eventually. :slight_smile:

Thanks so much for the support.