ArduPilot Mega not working with 6V Battery

Hi All,

I got an ArduPilot Mega from SparkFun which seems to have a common problem with the firmware not being loaded correctly. The inputs could not be read and when changing to manual mode, the output and MUX light would twitch very rapidly.

After getting a BusPirate, I flashed the ATMega328 with what I believe are the correct fuse settings (DFFF & FE), using the provided .bat file.

The board is now working consistently when I connect it via USB (using the 5V IMU board or with the 3.3V FTDI Basic Breakout). I would like to power it with the standard setup I have in my glow powered model plane, which has a 6V battery, but the PPM encoder does not seems to work when the board is powered by a 6V battery. I am powering it via the receiver, not directly.

When powered with the 6V battery, the PPM light stays on (does not blink) and the MUX light is also always on (does not read the input from IN7). I've measured the voltage in the board on both scenarios:
 - Powered by USB: Output reads 4.99V
 - Powered by Battery: Output reads 6.55V

I would consider feeding the received with a voltage regulated input, but the ArduPilot Mega manual states that it can be powered from a 7V to 14V source (, which leads me to believe that something is not working correctly (maybe the internal voltage regulator).

Does anyone have any suggestion on how I can troubleshoot this problem?


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  • "7V to 14V source" - be careful w/ the higher voltages I have had heat problems w/ an 11.1V 3S.

    Check out this page regarding powering the board:

    Also, be careful when plugging in the servo cables, if you plug the positive into the signal on accident, you'll fry the mux
  • I guess that I now have 2 options:
    1. Use the internal power supply, if the drain will not go over 1A (the peak limit on the LM317);
    2. Get an external power regulator, if the setup requires more than 1A;

    Thanks for your clear feedback.
  • The voltage regulator only works for power supplied from the external battery input, which should be greater than 7.4V.

    Feeding power from the receiver inputs you bypass the regulator - there is no regulation, and at 6.55V you are overvolting your APM!, hence no worky.

    There is no way to get a suitable voltage using your current setup. Your choices are to do as TCIII suggests and feed the battery input from a >7.4V source, or provide your own regulated 5V supply.
  • Admin

    I do not believe that the APM is designed to work on a direct input of 6.55vdc from the receiver. It might be best to power the APM through its 5 v regulator input and separate the APM power from the servo power provided by the receiver.

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