I've got a problem, hopefully someone can help...I've got a stock Hawk Sky, with a 2200mAh lipo, that I am trying to set up an APM2 in.  With the APM2 installed, and powered through the input output rail,  I'm only getting 20 to 45 seconds of flight time before the ESC hits the low voltage cutoff, and shuts down the motor.  I get 8-12 minutes of flight time with the same esc/motor/battery combo if I don't run the APM2.  By watching the telemetry, I can tell that the voltage drops very quickly.  I've tried unhooking the xbee and current sensor from the APM2, but I still have short flight times. 

I've been struggling to troubleshoot, and have no idea why the AMP2 would cause such large voltage drops.  I thought the APM2 only draws 300-400mAh, so it shouldn't cause such a large draw.

Would using a separate BEC (pulled off the same battery) for the output side of the APM2 help, or do I need to step up to a bigger battery, or should I replace my ESC?

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Is your APM2 powered through the ESC output?

The max input voltage for the APM2 is 5VDC.

Some ESC outputs are programmable and can go to 6VDC to support receivers/servos that use it.

Yes, it is powered from the ESC output, which is 5v.  I'm not having a problem with the APM2 cutting off, since the Low Voltage Cutoff from the ESC only takes power away from the motor (i can still control the plane in the sky when it cuts off, but I have to make a glider landing).

When this does not work, is the ESC throttle line being driven by the APM2, or is the APM2 only leeching power from the ESC and the throttle being driven by the receiver output?

What else is connected to the APM2 when this condition occurs?

Do you have sufficient adapters to measure the current drain of the APM2 in the 'bad' situation?

You should be able to remove your prop and set this up on a bench to test it -- minding heating the motor and ESC.

I just realized that I slightly mis-wrote my initial post...i meant to say that the APM2 is powered through the OUTPUT side, which is the normal setup I believe.  I have the ESC throttle line attached to the APM2 outputs, so this powers the board and the servos.

I've detached all other peripherals, including the Xbee and the current sensor, with no effect on the quick voltage drop. 

How would I measure the current drain from the APM2 directly?

Hmm, I'm a multicopter hobbyist at the moment so I have not set up a fixed wing bird.

To measure current, you would have to have an adapter wiring to allow in series connection of the power to the APM2. Break into the red lead but use a servo extension for this, not your original wiring.

The connections would run through the current inputs of your DVM. DVM usually have a separate 'A' jack or something like that.  Check out THIS video. In your case, I would start with the '10A' jack.. if you have one.

If you put too much current through the lower amp jack, you may blow the internal fuse. If you blow the 10A fuse with the APM2 in series. Something is seriously wrong.


The diode on APM2 output side is only rated at 500mA, if the voltage is dropping as fast as you say it is because of some short then the current would be way higher and would've blown that diode. The voltage anyway on that side is only 5V and your flight battery should be 12.6V (3S) or 8.4V (2S) (you didn't say). The flight battery should be connected directly to the ESC and not go anywhere near the APM.

Measure your flight battery's voltage directly not through telemetry and then try, see if you get the voltage drop then?

Sounds like a duff battery or ESC - even your 8-12 minutes without the APM is poor. If the APM is consuming a full charge in 20 - 45 seconds it would be red hot.

Do you have a spare ESC that you could try?
Are you sure the battery is getting a full charge?

So, I think I've fixed it. I noticed that the stock ESC was heating up, and with Paul's comments in my head, I purchased a new ESC and mounted it outside the cockpit.

I just had my first flight with it, and it ran for almost 20 minutes, with much more power at hand. I had no idea this plane could fly this well!!!

Anyway, thanks to all for the input, I'm off to troubleshoot other problems... (With the telemetry link after upgrading firmware)

Good news, enjoy your Blixer and good luck with your troubleshooting


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