PIXHAWK powering critical attention points - Wiki complementary information

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

Views: 7434


3D Robotics
Comment by Chris Anderson on June 15, 2014 at 1:22pm

Thanks, this is great. Do you need wiki access permission to add it there? If so, PM me and I can arrange that.

Comment by Timo on June 15, 2014 at 3:52pm

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.

Comment by naish on June 15, 2014 at 5:44pm

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. 

Comment by Joe on June 15, 2014 at 8:53pm

You say that "power port ground is NOT (connected to) the ground of the main output ports on the Pixhawk board"

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


MR60
Comment by Hugues on June 15, 2014 at 11:35pm

@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 ? 

Comment by Hans Miller on June 16, 2014 at 2:34am

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?


MR60
Comment by Hugues on June 16, 2014 at 3:52am

Hello Hans, cf links posted above .

About ground loops : if you do not connect the ground wire as advised with your ESC signal wire, then the current will flow otherwise in finding another "return path" and the ESC signal will be disturbed, causing synchronization problems with your motors. See video here :

Comment by turdsurfer on June 16, 2014 at 5:48am

Saying there is ground isolation when there is none can be very misleading. For a while a was surprised and elated by the OP. The root of the problem is that ground potentials have varying small differences between the FC and the ESC. Connecting ground from ESC to FC will alleviate that problem, but introduce new lesser problems (ground loops & possibly other side effects of a rapid varying ground in the FC). The proper solution is to use OPTO ESCs. I think that this ought to be the standard. Unfortunately there aren't many to choose from for multicopters.


MR60
Comment by Hugues on June 16, 2014 at 6:44am

Hi Tud, about ground loops :you're right that ideally no ground loops would be best. Unfortunately they can't be avoided here to establish a good ground reference for the ESC signal wires. Luckily though we are talking of very small currents and votages on that side of Pixhawk. Indeed we are not talking about ground loops on the battery high voltage side.

I do not think that opto ESC is a good reason not to connect your ground wire. There is no case that justify to connect a signal wire without its reference level...

Comment by Mike on June 16, 2014 at 7:09am

This is not a challenge to your recommendation  but it would be nice to know why you advise against connecting a BEC power source to the RC In Port (or by extension, the receiver?

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