Hi all,
I am building a new copter and currently thinking about wiring.
I have a 3DR 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
all +5V signals seem to be connected but only three gnd lines.
My first question is: why?
There is an older discussion 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?
Thanks a lot in advance,
Thorsten
Update: Also posted in the APM forum
Replies
No one else concerned?
I think this diagram is lying. Not all +/- are connected to the battery, which you would expect. It also doesn't make any sense whatsoever to have a 5V ESC coming back to the board (even one of them). The current sensor board outputs the power for the APM, not this board (may be historical for some reason).
That extra wire is probably to connect a video transmitter to it, which sometimes accepts 7-12/15/18/25V, so it's connected directly to the battery.
I think you should do a conductivity test on this board instead to see what is connected. The grounds do not need to be connected, because in my experience most ESC's have this properly wired to the ground of the PWM signal.
I would indeed follow the advice not to connect all 5V/GND's of all ESC's, but only one of them. The difference is that the 5V regulator may have a slightly different configuration, which may cause ground loops or currents to flow between the ESC's on the input side. If that happens, it's possible you get misinterpretations of the PWM signals leading to the motors, which eventually can cause crashes. All stable quads I know are wired with one ESC providing voltage+GND and the others just leading the signal cable. The voltage difference, if any, is rarely large enough for motors not to work. If it does happen, it may be needed to add the GND as well at some risk.
You are right the diagram is lying!
But:
- According to a conductivity test all +/- connectors of the ESC servo wires are connected on my PDB.
- The extra wire should be connected to the Main Out of the Pixhawk (see below).
- If - as you say and as suggested by Randy et al. - this could lead to crashes I am wondering why they distribute the PDB as is?! If this could really lead to crashes is careless and grossly negligent and I am wondering why no one is answering over here and in the APM Forum... Hence, I would be happy if someone can confirm that one should or should not connect all + wires but only one.
Moreover, the cables connecting the PDB and the APM/Pixhawk are crap! They come off very easy. I complained about it a while back but did not receive a reply/comment...
Additionally, what is the correct connection of the + and - (red and black) cables to the PDB?
The one shown in the 3DR store:
Or the one shown in the wiki: