I'm reading here http://ardupilot.org/dev/docs/raspberry-pi-via-mavlink.html that
Has anybody ever run into trouble powering it via Pixhawk's telem and not via its USB?Powering via USB is recommended as it is typically safer - because the input is regulated. If powering via USB, do not also connect the +5V pin as shown (still connect common ground).
To power the Pi from USB, is there a recommended approach? Micro USB to Pixhawk's BEC powered servo rail? Micro USB to standalone BEC?
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Oops good catch, there was a typo in my diagram, I meant to connect the servo rail +5V to the GPIO.
telem2 RX ------------------ Pi GPIO TX
telem2 TX ------------------- Pi GPIO RX
servo rail +5V -------------- Pi GPIO +5V
servo rail GND ----------------- Pi GPIO GND
OK so to make things simple I'll go with the UBEC powering the servo rail, and the Pi attached to the rail via its GPIO. My servo rail has a Zener diode + capacitor, hopefully that helps protect from peaks and noise. I understand this is not as ideal as connecting directly to the Pi's USB power. At least this powers the Pi independently of the Pixhawk.
Do I understand that I basically end up with the following, especially with the Y shaped GND path?
PH telem2
+5V ----------------- servo rail +5V
RX ------------------ Pi GPIO TX
TX ------------------- Pi GPIO RX
GND ----------------- Pi GPIO GND
\---------- servo rail GND
Stupid question: since there's no proper ground/earth onboard the vehicle, what is used instead?
@James - instead of soldering directly on the RPi board, why not use the GPIO pins?
My servo rail is powered with a 4S LiPo and this uBEC: https://www.amazon.com/Ship-Hobbywing-Switch-mode-UBEC-Lowest/dp/B0...