Pixhawk traditional heli power confusion

[Dan_555]

Hi everyone,

I'm working on setting up a Pixhawk on a large traditional heli (trex 700 DFC with HV servos.) I'm quite confused about how to properly provide power to the Pixhawk and servos/rx. If I understand correctly I should provide power to the Pixhawk via the 3DR power module to the 6 pin "Power" connector and to to power the servos I must also run power directly to one of the connectors on the servo rail? I have read conflicting reports on powering the servo rails, can I provide direct 2S lipo power to the servo rail or do I need to step this down to 5V with a regulator?

Thanks!

Dan

[R_Lefebvre]

Dan,

You basically have it. The 3DR Power module provides power to the Pixhawk flight controller only, via the 6 pin connector. Note that the 3DR PM is ONLY rated to 4S. There are other manufacturers such as AUAV who manufacture PM's with higher voltage capability.

You then have to power the servos with a BEC. The servo rail can tolerate up to 10V. If the voltage on the rail is 5.0-5.6V however, the Pixhawk can draw from the servo rail as a backup to the PM, allowing redundancy. Or, you could power the Pixhawk without the PM, simply supplying 5.0-5.6V to the servo rail.

Note that the Pixhawk servo rail cannot handle the current from 4 high performance full-size heli servos. 10A max, I think but I wouldn't even do that. I would not use the Pixhawk servo power rail to handle servo loads on anything larger than a 500 heli with mini servos.

On everything else, I construct a servo power breakout board. Or you could use any of the various systems already available for a helicopter.

[Dan_555]

Thanks for your help Rob, I'm really glad you mentioned the 10A max issue as I was planning on using the Pixhawk servo power rail to power my 4 HV brushless servos! So to power the servos would I simply connect the + and - servo leads to a separate BEC and connect the signal leads to the pixhawk? If you have any reference images of how you wire your setup that'd be awesome!

Thanks again,

Dan