I've posted about this before, but I feel I must reinforce this:
You MUST use a completely independent power supply for your APM or Pixhawk than you use for the Servos. DO NOT use one BEC to supply both the Servos, and the APM/Pixhawk.
On most of my helis, I use a 2S battery direct to HV servos, with a separate regulator going to the Flight Controller. On the rare case that I use a BEC for the servos drawing from the motor battery, I use a completely separate BEC to power the Pixhawk.
This is vitally important.
One user suffered a bad crash on Saturday because of this. If you use a single power supply, the servos will eventually cause a brownout, and you will have a crash. It's just a matter of time.
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Excellent post Muhammad, thank you.
The APM/Pixhawk definitely is less robust to brownouts than standard,high quality RC stuff. Hence the warning to use suitable power supplies for them. The alternative of trying to make the APs more robust and continuing to use power with big holes in it is not a good permanent solution.
I have been using the supplied APM power module that comes with the Pixhawk so that gets a constant power from an external battery then I use a BEC to the servos.
Yep, that's fine too.
Thanks, Rob, for pointing that out.
Two questions:
1) I was going to build my HK 450 with exactly that single power supply because I considered my YEP 80A ESC with its 6A BEC strong enough for both the APM and the servos (4x TGY 306g). This is wrong, I assume?
2) If instead only the APM (and the motor) is powered by the YEP and the servos by another BEC but everything from the same battery, is this okay?
All the best, Markus
1) Yes, this is wrong. The problem is not that the BEC can't feed the servos on a continuous basis. The problem is that even when using a BEC with ample capacity, the servos can can cause large positive and negative spikes. Both can cause this problem. Obviously low voltage is a problem. But servos can also cause high voltage spikes when the motor decelerates quickly ( inductance ). If the Servo rail voltage goes over 5.7V, the power controller on Pixhawk shuts off that supply, so it will cause a brownout.
2) Yes, this seems like a reasonable thing to do. Use the ESC BEC to power the Pixhawk/APM, and then use an external BEC for the servos. Especially on smaller helis. On larger helis, I still prefer the 2S/HV Servo route.
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