3DR PDB and APM powering

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1
  • Also posted on DIYDrones, but might fit better here -

Hi all,
I have a 3DR hexa PDB https://store.3drobotics.com/products/hexacopter-power-distribution-board-1 and I am not sure if I should use it for connecting the ESC signals to it to connect to the APM/Pixhawk. My problem is:
If you look at the schematics

[attachment=0]schematic.jpg[/attachment]
all +5V signals seem to be connected but only three gnd lines.
My first question is: why?

There is an older discussion on DIYDrones (http://diydrones.com/forum/topics/connecting-esc-directly-to-apm?id=705844%3ATopic%3A272862) on Connecting ESC directly to APM . There are two comments from Randy and Sandro saying that it „is not recommended to use BEC from all ESCs at same time“ and that „you need to take it from just one of them“.
So this is in contrast to the schematic - if I read it correctly.
I know from my own experience that both - connecting all ESCs directly with all +5V signals connected as well as connecting only one +5V signal - work.
So my second question is: what is correct and recommended technically?

My third question is: what is the correct connection of the + and - (red and black) cables that go to the APM to the PDB?
The one shown in the 3DR store (+ = black):
https://store.3drobotics.com/products/hexacopter-power-distribution-board-1
[attachment=1]3DR-hexa-PDB-assembled.jpg[/attachment]

Or the one shown in the wiki (+ = red):
http://copter.ardupilot.com/wiki/initial-setup/assembly-instructions/
[attachment=2]power-wiring.jpg[/attachment]

Thanks a lot in advance,
Thorsten

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Hi 3DR Support,

some answers would be nice.
The schematic is wrong as is the connection of the red and black 2 wire cable from the PDB on the image you are showing on your store webpage!
I am still seeking for an answer why all + and - signals are connected which is not recommended by Randy and others?
Copters and not stuffed animals. Hence, anything that can lead to dangerous situations should be avoided…

Thanks in advance,
Thorsten

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Hi 3DR Support,

there seems to be confusion about if and how to connect NO or ONE or more than one ground and power wires from the ESCs to APM and Pixhawk. And the behavior of the two systems (APM/Pixhawk) seems to be different too:
http://ardupilot.com/forum/viewtopic.php?f=21&t=6093
Please, please shed some light on it!

Thanks,
Thorsten

4

No need for the PDB. Its bulky and poorly designed, at least for my 3DR Y6.

The reason you dont want to connect all +5V from the ESC´s is that the voltage regulator for each ESC might get overloaded due to differences in output from each regulator. Let´s say one regulator is giving 5.03V and anotherone 4.99V … if put in parallel they will work against each other trying to regulate the voltage to their own specific voltage level.

In short, remove the red wire from all but one of the ESC´s and use the last one to power the system. If you got the Power Module you should remove the +5V wires from all the ESC´s.

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Thanks Andrew!

That’s what I am doing now. I had no problems so far with connecting all wires but if this is problematic it should be avoided.
What I do not understand is that there is no information/waring somewhere in the Pixhawk manual or in the wiki. And no comment or reaction from 3DR on this and the wrong wiring they show on their webpage and on their (wrong) schematics of the PBD. That’s strange…

Kind regards,
Thorsten

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Attached is another view of the hexa PDB (eagle ratsnest) where you can see all the vcc are common and all gnd are common.

3DR ESC’s BECs are linear type and they work fine connecting them in parallel. I heard that ESC with switching mode BEC can’t be connected in parallel.

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Thanks Rogelio!

I also send an email to help@3DRobotics.com. Here is the (relevant part of the) reply:

[quote]“It seems that the board file is outdated, all ground pads are common and all positive pads are also common.
The overload would depend on the quality of your BECs, the ones we sell have not shown behavior of these kind.”[/quote]

Not sure if this is the answer I expected…
There must be some more general advice I guess. So for now I do not connect any of the +5V from the ESC to the Pixhawk and only one to the APM.