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
Hi Adam, on my fixed wing, I do not use a PDB. I connect a 10A capable BEC on the servo rail of pixhawk. You could use multiple connectors soldered on the BEC output.
Hi, what PDB would you use to wire a BEC to if it was being used on a Pixhawk on a fixed wing platform (single motor) ? I would also appreciate you view on whether that PDB could be used to power other ancillary systems such as a video transmitter or gimbal?
Hello Justin, the dual power port and servo pins power connections is for redundancy. There are two possible ways to connect a secondary power source to the servo pins: either a dedicated BEC, either an ESC BEC. As you understood, this is for power redundancy. Concerning your criticism of diyd approach, In the full respect of diyd spirit, I explained and refered to links giving all the detailed explanations that resulted in this diagram post;
I will try to clarify what appears to be confusing , sorry if I use the wrong vocabulary (not my native language):
-the white signal wire (or sometimes yellow) of the ESC is used to carry the signal to control the motor (rotation speed) . An electrical signal needs a level reference to be correctly "read" by an electronic circuit. This level reference is called "ground"; and corresponds usually to the black wires in our usual rc wiring.
-For Oliver, the servo rail of pixhawk is the rail of pins where you connect the servo wires.
Oliver, if you want to help with some pictures illustration, you are welcome...
@ Hughes:
Exactly, those words make no automatic sense to anyone except the already initiated. And now I'm really confused: We are to connect signal and ground wires together?? And some will ask, "What's the "servo rail"? This is what I'm talking about. A "diagram" with name labels again assumes knowledge, and a common language (which is perhaps a problem here). Photographs do not require any knowledge or a common language. This is why every decent equipment manual has at its core photographs. The work is appreciated, don't get me wrong. But it is not at all clear how to apply it.
So can you explain why you choose to connect the BEC to the power port as well as the servo pins on the end? To my knowledge there is a diode inside the pixhawk that allows the servo bec to power the pixhawk, therefore the Y connection is redundant. I think one of the things that sets DIYD apart from other rc fourms is more scientific rigor and less "heard this is the best way to do it" and I would like to see the reasoning here for your proposed changes.
As an additional topic, what is the potential source of the >5.6v spike is coming from that the zenier will clamp?
Added note:
Opto-isolator breakout boards can only be used with ESCs that have BEC (i.e. not real or fake 'opto' ESCs).
I just tried one of these cheap opto-isolator boards between my ESC and a separately powered servo tester and it works fine:
https://www.sparkfun.com/products/9118
That's a cheap solution to get the best of all worlds. On the Pixhawk side both signal and ground are connected. On the ESC side, all 3 wires are connected.
@Oliver, a drawing is better than 1000 words, therefore a diagram. There is no discussion: ESC signal wires have to be connected with a ground black wire on pixhawk servo rail . That is the loud and clear message.
This discussion is way too confusing and has way too much confusing terminology. Perhaps someone could put some photographs of the appropriate and inappropriate wiring connections together. Shocking as it may be to Joe Q. Engineer, there are scads of folks out here who don't know anything, and couldn't care less, about the differences between "ground," "ground reference," ground isolation," ground loops" and for that matter ground beef. If there is indeed a problem, kindly please show us (not "tell" us) exactly what wire to run from exactly where to exactly where. Thanks.
@mark, You're right that with APM as long as you have a ground wire already connected, all the rails of that board will get the same ground reference (even with JP1 off). And therefore you may only connect the signal wires. I've always done that too on my APM boards withtout any issues.
On Pixhawk, it's another story (don't ask me why but that is so). Doing the same has apparently caused unstable or uncontrollable crafts, according to the diydrones and support forums posts talking about this. It traces back to a lack of and/or bad ground reference causing unstable motor PWM signals.
If you're using APM, you're thus ok with the way you describe your wiring.
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