I'm building a hybrid UAV with a Pixhawk flight controller for use in a competition. As far as i've understood a requirement of the competition is to have a back-up power supply for the flight controller ONLY (does not power any actuators). I think this is to maintain contact with the UAV until it crashes if main power is lost.
My question is:
Can i use a small 2S (~7V) battery regulated to 5V with a BEC into the USB port while powering the pixhawk normally via main Power Port and then the Motors/Actuators via ESC/BEC's on the Servo Rail?
Second question, is there any difference between the vertical facing "USB" port and the side microUSB port on the Pixhawk?
My understanding is the pixhawk will have to loose power to both Main Power and Servo Rail before it uses the USB power, so i feel like it should be fine. However, in the past i have blown a 3.3V regulator on a Pixhawk and i suspect i did it by powering the main port and USB port at the same time while calibrating things. Not sure on this.