I'm looking for an electrical explanation of the statement here:

Warning: Do not connect power (red + & black -) from the RC10 (A10) & RC11 (A11) connectors to the servos, just use the signal lines. Power the servos via the PWM Outputs connectors. These solutions will avoid the scenario that can possibly happen when the Pan/Tilt servo draw too much current and cause the APM to brownout (reset)

I examined the APM2.5 board drawing and schematic here and the grounding is a little unclear. On the schematic, they all just go to GND, but on the board drawing some of the ground pins appear unconnected to traces. I checked for continuity, and there is no continuity between the PWM grounds and the A10/A11 ground pins. By the way, my power setup is that I have J1 enabled and I am using an ESC to power the board.

Can anyone figure out, electrically, what is between these two sets of ground pins?

Ground pins appear unconnected to the traces:

Ground pins appear unconnected to the traces

PWM ground just connected to GND:

PWM ground just connected to GND

analog output ground also connected to GND:

analog output ground also connected to GND

  • $\begingroup$ Can you upload an image of the schematic and link to it from this question? $\endgroup$
    – Ian
    Jun 28 '13 at 16:17
  • $\begingroup$ Ok, I've cut out the relevant bits of the schematic and the board diagram, and added them. $\endgroup$ Jun 28 '13 at 18:26

I found a possible answer for you here:

A10 & A11 are connected to the input rail because historically those were inputs and the Vcc rail was used to power the sensors. When you attempt to power servos from the input rail, the extra current draw causes an additional voltage drop across the input diode and fuse and Vcc drops to brownout levels regardless if you are using a BEC or the Power Module. If you are going to connect servos to A10 & A11 you must provide an alternate source of power not Vcc from the input rail.


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