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.
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...
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.
@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.
Thanks for the kind words Hugues! That diagram could not be clearer and should be added to the wiki.
I have my Pixhawk powered both through the power module (PM) and the servo connectors going to my 4-in-1 ESC and so far one out of one flights has been successful!
@Mark, To add to the confusion, it sounds like your opto escs aren't really optically isolated, but simple don't have BECs. An optically isolated ESC shouldn't work with only the signal wire connected.
Hello Mike : about RC IN, this is a practical experience reported by some users on the support forum who have reported problems doing so on pixhawk. Until this is fixed or formally tested otherwise, let's choose the safety side (that is : use another port to power Pixhawk from the output ports).
@Tud : let's not mix two subjects for other readers : ground loops / ground reference. You're right that Opto ESCs will avoid a ground loop through the ESC (we will not avoid another potential ground loop though as shown on my diagram when powering the pixhawk in backup mode both from the power port and the output ports). About the other topic, ground reference, we still need a ground reference even with an OPTO ESC, as you say.
Hello Mark,
Whatever the board, you always need to make sure that your signal wires have a ground reference to be stable (APM od Pixhawk). Let's not confuse two different points: having a ground reference and ground loops.
So to answer your question 1): yes you need to connect at least one ground reference wire to pixhawk/APM, independently of the ESC model you're using. A fortiori if you use an Opto ESC you should make sure that the ground wire is connected with its signal wire. This is the same principle , APM or Pixhawk.
Question2) : no there is no difference, Opto or not Opto, as far a ground reference is concerned : you always need a ground reference for your signal wire. (The Opto thing discussion was about avoiding a ground loop going through the ESC, which is another point).
Hopes it helps to clarify, otherwise shoot more questions !
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