As a general rule of thumb, two aspects are important:

  • It is important that the power module is connected and providing power to the system
  • The power module is NOT suitable for powering servos. It is solely intended for the autopilot - so the system needs an additional BEC or an ESC with integrated BEC.

Battery Connections

This page describes the operation of the PX4FMU and PX4IO power circuits and how to connect batteries for flight. The power routing on the PX4 boards is designed to do the right thing in most circumstances. The stack will take 5V from the servo connector, from USB, from the expansion connector or from the 15-pin connector on PX4FMU. PX4IO or the power brick will accept up 18V input at the battery connector, and the power brick / onboard BEC can supply the stack with up to 2.25A at 5V when powered in this fashion. You can connect as many of these sources at once as you like - the stack will Do the Right Thing. It is however NOT suitable to power servos or any other actuator - it only is intended to power the autopilot and GPS.

PX4FMU v1.7 / PX4IO v1.3

For high-voltage servo systems, you can remove a component from the PX4IO board to isolate the servo power rail from the rest of the system. This is required to avoid overdriving the stack's internal 5V rail, and in this case power must also be supplied to the stack via some other means.


FMU v2 / Pixhawk is high-power servo rail ready out of the box. Note that in this mode the servo power supply however is not any more used as backup power supply - so the power brick will be the only supply source.

Warning: the RC input is not connected to the servo power rail, so never use the receiver to power HV servos. Power to servos should be supplied through any of the other connectors except RC. The life of your system depends on that rule !

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