I have purchased a separate BEC to provide the 5V supply for the processor board and the Radio receiver, rather than use one of the four that come with the motor control ESCs. The reason for this is the uncertainty that still seems to surround the random blowing up of mux ports, which seems to be related to possible misbehaviour of these BECs when connecting and disonnecting USB power when a LIPO is connected.


Please can you advise me whether I have the changes correct here:

1. dont connect the 5V wire from any of the ESCs

2. Connect the inputs of the separate BEC to the LIPO supply somewhere convenient on the power distribution board.

3.Connect the 5V output of the separate BEC to the 5V rail of the right-angled radio receiver connectors


Should I put a shottky diode in series with the 5V BEC output so that the USB supply isn't trying to drive the BEC when the LIPO is disconnected?


Thanks for your help. Awesome project guys.



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This is what I have done - but did not try the diode - that sounds like a good idea.


But I am still confused about the warnings that say to have battery plugged in first then USB so as not to burn the ardu outputs.

Also I have burned the right front motor (twice) using this set up with battery plugged in then pluging in USB. once was in CLI mode, the other was in regular flight mode unsing Pid configurator. shortly after the USB was plugged in that motor strated rocking back and forth rapidly and blew before I had time to unplug the battery!!!

My question is with the red ESC wires cut can you run the board on USB power alone? or is the advice about plugging in battery first good for the outputs but bad for the motors?. My motor wires are soldered so disconnecting them is not a viable option


Al, when you connected up your additional BEC, did you connect both the input and output black wires of the BEC together?

It seems to me that one has to do this, because the ESC signals need a ground, and LIPO ground and ESC ground are joined on the Power dist board.


I note also that you do not need to cut the red wires from the ESCs, since these signals don't go anywhere on the power dist board, provided you dont connect the red output wire to any of them. I connected the red output wire directly to the BEC output via a schottky diode, bypassing the power dist board completely.


Your note about motor burning is worrying. For bench testing, I'm thinking of making up a battery extension cable with a big switch in line so that I can isolate the LIPO quickly.  How long do motors take to fry?

I use a Castle BEC for my projects wired as you listed.  However, I do not use a power distro board since I run different frames - I plug the BEC power into one of the free ports on the APM.  Have not had anything fry (yet).  I do not run a diode, but I do have the motors spin up when initially connecting via USB to CLI.  Can not duplicate if I connect to APM via XBee so diode might not be a bad idea.  I have only been using ArduPirates code and have not had a chance to try AC2.

Sure you can use external BEC's. We are using external BEC's on all our ArduCopters. If you don't use any Power Distribution PCB, easiest way to separate BEC powers coming form ESC's is just by cutting center wire (usually white) and then just hook up your BEC to APM RC rails.


If you do use ArduCopter PDB, then just leave out that power connection (red/black) cable and use output cable from your BEC

i think that the newer version of APM is protecting USB and preventing it to feed the RC rails.

the proof is that my receiver is connected to the APM rail, but when plugging the USB, it won't power the receiver.

Ok this is all interesting.

I am not using the distribution board - so that us why I cut the red power lines from esc connectors.  The esc main power leads come off a power hub from main battery, which also feeds the castle BEC so this should mean the escs, BEC and subsequently the APM all share a common ground.

Definitely with battery, then connecting USB, motors (usually right front) do spin to various degrees while communication is established. There after sometimes I get ongoing motor beeps.

So the question is - if the new APM have added circuits to protect outputs, can I just leave the battery unconnected during any USB work.

I have ordered XBees so hopefully will minimize direct USB connections


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