Hi,
Integrating troubleshooting results from quite a few people describing power problems with Pixhawk or Pixhawk getting out of control (linked to ESCs' signal wires connected without a ground reference) I thought the current wiki information should be completed/updated with a synthesized diagram that says it all clearly and explicitly.
This diagram represents optional components that you may have or not but the wiring logic remain the same.
The basic fact to know to start with is that the power port ground is NOT (connected to) the ground of the main output ports on the Pixhawk board, contrarily to what we were used to on the APM board (where the ground was the same on all ports, inputs or outputs).
Acronyms on the diagram: PDB on the diagram means Power Distribution Board. PM block means the power port of Pixhawk. PM/Atto means an optional power module from 3DR or the Attopilot alternative for higher than 4S battery voltages.
Any comments to add eventual useful tips that would be missing are welcome. I'm not the best at drawing stuff, so if Jethro (known for his excellent illustrations) or some other guy here on the forum has graphic design talents, this diagram could be made more sexy.
Hope this will help some folks to do a safe wiring.
cheers,
Hugues
Comments
It would be nice if someone could clarify who is right here. Otherwise some of us may start panicking. Also what of ground loops on multiple switching becs?
@Naish, good advice, I will add this to the schematic. As for the diode, adding a capacitor must be done with as short wires as possible, otherwise the capacitor will have no effect. It is good to try to connect it, like the zener diode, via a standard 3 position servo connector (no wires at all).
@Joe, I summarized what has been discussed, written and concluded by many experts and just to name a couple that I believe without any doubts: Craig3DR from 3DRobotics and Lorentz Meier . The diagram, what I summarized , is a synthesis exercise from many posts that aims at making people do their wiring right (and not so much to be an exact undsiputable PCB or electronics layout). I refer you, if you want to drill down this matter by yourself, to some of the posts where this has been said/written/discussed/concluded:
http://ardupilot.com/forum/viewtopic.php?f=21&t=6463&start=20
http://ardupilot.com/forum/viewtopic.php?f=80&t=6780&start=20
http://diydrones.com/forum/topics/pixhawk-causing-motor-sync-issues?commentId=705844%3AComment%3A1620884&xg_source=msg_com_forum
http://diydrones.com/forum/topics/pixhawk-causing-motor-sync-issues?commentId=705844%3AComment%3A1627206
https://groups.google.com/forum/?hl=en&fromgroups=#!topic/drones-discuss/aR4g9sz9ssE
http://pixhawk.org/users/actuators/pwm_escs_and_servos?s[]=pixhawk&s[]=pwm&s[]=ground
http://diydrones.com/forum/topics/pixhawk-causing-motor-sync-issues?xg_source=activity
(and this list is not exhaustive)
In short we have to interpret this diagram, not as an exact PCB schematic, but as a diagram that tells people how to connect their wires right (even if by essence a diagram never reflects coorectly/exactly real physical/pcb components). When I say "ground isolation" that seems to bother you on this schematic, it is meant to say : do not trust that a ground wire on the power port will allow you not to connect the ESCs motor signal without their corresponding ground. There is no other message. If you want I can adapt this sentence on the diagram, suggestion ?
Also, above your diagram you state that there is "Ground isolation between power port and PWM ports on pixhawk"
However your emphatic statements do not appear to match reality, see the screen capture above from the pixhawk Eagle file for the PCB, when I click on "SHow" on any output GND pin, the Power Module socket's 2 GND pins [highlighted BLUE] also get highlighted - meaning they are indeed connected and NOT isolated.
It would seem to me that if indeed there is a difference as to where you make the GND connection the difference is not due to any GND ISOLATION.
Can you please show me where in the pixhawk Eagle schematics or PCB file you see a GND isolation
I will strongly advise to put in the schematic an optional 3300uF 16V Capacitor to smooth out the power rail and avoid brownouts. Is a cheap solution, but can save you form a crash.
I was just curios if this although applies for the PX4IO. I just checked that and it seems that it is not affected. The PWM output ground ports are connected to the battery ground.
Thanks, this is great. Do you need wiki access permission to add it there? If so, PM me and I can arrange that.
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