Does Pixhawk require ESC return ground signal?

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1

I’ve posted this also on RCG, would much appreciate 3DR support chiming in, this has been a serious problem for me. In short: I’ve had problems swapping a 2.5 board with a Pixhawk, with the same exact ESC configuration and wiring known to work for 100s of flights on an old board. Problem seems to have disappeared once I added ground signal connection to output rail.

(Edit add: All escs always calibrated one at a time through direct connection to receiver.)

More below (sorry, a bit long).

I’ve had some serious issues to date with Pixhawk, that I may have resolved, and thought I’d share here. This may be related to what kfennel has been experiencing. In short:

Swapped apm 2.5 with Pixhawk on a long tested and perfectly flying “kamikaze” quad (thank god, read on, as the pixhawk is ultimately for my heavy octo). Couple details, which may be crucial in this case:

  • No use of the 3DR module, as I haven’t upgraded yet to a 6S capable sensor. So Pixhawk is powered on spare pins with a 3A bec.

  • All esc’s plugged with signal wires only.

Results: Calibrated everything accel, etc …, first go: Flip.
Calibrate Escs. Flip again. Replaced what I thought was a bad esc, damaged motor from flip, this time plugged with ground wire re-calibrated. Flip. Recalibrated all escs. Success …
Go through a battery. Switch battery. Flip again!

Read viewtopic.php?f=21&t=5838

Replaced all escs with new ones with ground signal plugged also: Success. Power off, switch battery. Success again, all good.

My bottom line so far: The combination: external dedicated bec power/no 3DR power module + escs with signal wires only + (maybe) taking a while pressing the safety switch => problem. Escs are vanilla simonk flashed afros, worked for hundreds of previous flights with apm 2x boards with signal wire only.

The case for using an external bec and not plugging in esc power wires is well established. (“clean” power, avoid crappy esc’s internal regulators, less wires plugged in => better FC vibration isolation). But … not plugging ground wires is less established, original idea is to possibly avoid ground loops. Yet I’ve never read reports of problems using the ground wires. In any case, could it be that Pixhawk’s internal wiring/rail ground plane is different than 2.x boards in that it does require an ESC return path? Or is there some weird ESC bad initialization (or bad recalibration) sequence when ground wires are not present? There is also something about enabling the safety switch fast after powering up (I think I read a message about this from Randy somewhere, to prevent unwanted calibration…). So far I’ve tested enabling the switch after more than 30 seconds (with esc’s with ground) and no problem …

Thoughts anyone? Needless to say, “miffed” is an understatement …

My “problem” is fixed for now, and the pixhawk copter flies fantastic, stabilize, acro, loiter and all. (although I still have some trim issues, but this is probably unrelated). But I don’t like not getting at the root of this. Let alone rewiring dozens of ESCs to provide for ground connection …

2

More information in general about ESC and pixhawk would be awesome. Do they need a ground, do they have a timeout period on either side? I found today that I need to plug in the ESC’s first then pixhawk. Which is mildly terrifying with a large copter. Otherewise I have to plug them both in very fast together, or plug the pixhawk in. Then when I’m ready plug in the batteries and arm right away. If you don’t arm fast you wont be able to in that order.

Or give me a super reliable power supply for 6s that I trust more then a BEC on a separate battery so I don’t have most of these problems!

3

You need to have a ground reference connection between the ESCs and the Pixhawk.
Kevin, I expect this is why your ESCs are not working for you.

4

Craig, makes sense.
For some yet unknown reasons I’ve found that it actually depends for me, though: I just tested some different ESCs (Hobbywing 30A optos) with only the signal connected to Pixhawk and it works fine, I successfully completed several flights. I suspect the ground path requirement depends on the actual esc firmware, possibly the way the ESC “boot-up” sequence is implemented …

So far and to summarize, I’ve tested four brands of ESCs on APM 2.5 and Pixhawk.

APM 2.5: All brands work with only signal path
Pixhawk: One brand works, one other looses calibration, haven’t tested the other two.

5

I think I had the same problems with my AFRO esc,
Changed after many perfect flights on my quad the APM with only the signal connected to the pixhawk
After setting al up I got yaw problems and two flips with crashes, checked logs and uploaded them to this forum and no exactly pinpoint the problem so I changed back to apm
But the signal problem could be the issue, why is there no info about the return wire

In the manual only the following text.

Connect each signal wire from the PDB
to the main output signal (S) pins by
motor number. Connect one wire for
each motor to the corresponding pin.

6

The pixhawk has much more complex power circuitry with support for power supply fallback. You may in fact want to wire one of your ESCs 5v lines into the output rail as this will provide a fallback power supply.

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@jdennings, it is normal you get a weird behavior as you do not connect your power supply to poxhawk as per manual.
You MUST indeed connect one of your ESC servo three words connector to one of your pixhawk motor input. All others with just the signal wire.
If one day you decide to power Pixhawk with a power module connected on the power port, leave the ESC three wire servo in place, it will serve as backup power.

8

[quote=“Hugues”]@jdennings, it is normal you get a weird behavior as you do not connect your power supply to poxhawk as per manual.
You MUST indeed connect one of your ESC servo three words connector to one of your pixhawk motor input. All others with just the signal wire.
If one day you decide to power Pixhawk with a power module connected on the power port, leave the ESC three wire servo in place, it will serve as backup power.[/quote]

This is incredibly wrong. There is NO REQUIREMENT to leave one ESC powering the pixhawk. It is in fact an incredibly bad idea in many high performance cases. It is much better to have a small battery with a BEC powering the pixhawk as backup.

9

Not saying you are wrong, but would you care to elaborate this, please?
/ Tom

10

Not saying you are wrong, but would you care to elaborate this, please?
/ Tom[/quote]

Sure thing.

So there are three ways to power the Pixhawk during flight. You can use the power module through the power port, you can use a BEC through the power port, you can use an ESC power source on the servo rail, and you can use a BEC through the servo rail.

In many 2-4s applications powering the unit through the power module is fine, whenever the copter is only worth a few hundred bucks or isn’t likely to hurt someone for example. In this case not having redundancy is OK. Same goes for powering it through the servo rail off a ESC as Hughes mentioned.

Hughes says that you MUST use an ESC on the power rail through, which is very misleading. It is better to power it any of the other three ways if you are only going to use a single power. This is because the on-board BEC on the ESC creates heat and the main enemy of the ESC is heat.

So now I will mention that the Pixhawk has an Ideal Diode inside it. It will switch over seamlessly between the power port and the servo rail for receiving power if needed.

What some people are doing, and what Hugues is talking about in the second part of his statement is using one of their ESC’s as a backup power source to the power module in this way. Consider this though. If you wanted to have backup power and were therefore concerned about safety and reliability wouldn’t you want to do it the best way? Having a separate power source powering a BEC is the most reliable and easiest on your equipment. It is the only way to be sure you are not adding extra heat to your ESC’s.

Another thing to consider is that you dont know which side it is drawing power from, maybe you are working the power source on the ESC full time and you don’t find out till you crash…

So there, I hope this is clear, wrote this before my coffee.

11

[quote=“kfennell”][quote=“Hugues”]@jdennings, it is normal you get a weird behavior as you do not connect your power supply to poxhawk as per manual.
You MUST indeed connect one of your ESC servo three words connector to one of your pixhawk motor input. All others with just the signal wire.
If one day you decide to power Pixhawk with a power module connected on the power port, leave the ESC three wire servo in place, it will serve as backup power.[/quote]

This is incredibly wrong. There is NO REQUIREMENT to leave one ESC powering the pixhawk. It is in fact an incredibly bad idea in many high performance cases. It is much better to have a small battery with a BEC powering the pixhawk as backup.[/quote]

Are you reading what I said in its context? It is then totally right! You must have a ground reference , a unique one. That’s all I said to help the problem exposed by the poster. I was not talking about ways to power your pixhawk, what you try to put in my mouth.

12

They already have a ground from the main power line, what would plugging in one ground wire accomplish? And even if what you said was true plugging in the 3 wire connector would have the power plugged in which is often not desireable.

13

Add my name to the list of people with flip and crash issues with Pixhawk that didn’t exist on APM. At first I thought it was a ESC ground issue as discussed in this thread but that didn’t fix the issue. I’ve narrowed it down to a motor sync issue that only exists with Pixhawk. Check my thread on DIY Drones: diydrones.com/forum/topics/pixha … ync-issues and the following two videos:

[youtube]https://www.youtube.com/watch?v=i7_gVoY8q8M[/youtube]
[youtube]https://www.youtube.com/watch?v=VTK81IANyUE[/youtube]

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Great videos, I’m having the same problems after upgrading from apm to pixhawk,
many and many perfect flight with apm afro esc (with simon-k) sunnysky 980 and ezuhf
Never had problems with apm and chaning to pixhawk, 3 crashes suddenly upside down, irregular motor noise, not stable in air, WHATS GOING ON 3DR???

15

Shot another video last night using a seperate non simonk esc, seperate power module, same problem. I have contacted 3DR, I think I just have a faulty Pixhawk, but we’ll see what they say. Here’s a video:

[youtube]https://www.youtube.com/watch?v=7GJiYV2sAtM[/youtube]

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there’s no such thing as "return ground signal"
Pixhawk delivers a PWM elative to it’s ground. It’s ground is common to all of it.
In a perfect world, the ground of pixhawk, should always be equal to the ground on every other component connected, but if you measure voltage between different things - you can see a small difference because wires are not perfect 0ohm conductors.

We usually do NOT connect ESC gnd, to avoid ground loops.

you should measure voltage/ripple between ESC’s gnd wire, and APM’s GND. - you’ll find lots of noise.
now if you measure between ESC PWM gnd, - and ESC gnd in , it should be close to none. maybe a few mV.
You can continue that until you find the wire/device that have a resistance in it’s gnd wire or PCB trace - and give you a difference.

Remeber that your ESC already have gnd, from battery lead, where your power module is connected, and have two gnd wires up to APM, where the it’s connected to it’s GND, that is the same on PWM outputs.

17

@xoltri, any updates about the sync errors?

18

Yeah, I tried it with a completely different 2200kv motor on 3S that I use for my parkflyers and I had the same problem.

3DR said they will replace my Pixhawk. I provided them with my invoice from canadadrones as verification of my purchase. They then told me that they couldn’t find an order from canadadrones in their database, so they wanted me to contact canadadrones to verify the order that canadadrones made to 3DR.

I did send an email to canadadrones asking for this info but after I slept on it I decided that as a customer I should not be put in a place where I am verifying orders between the parent company and their authorized retailers. So we’ll see what comes of it now.

I’ve had this quad for a couple months now and this is just the latest chapter of problems so I am getting pretty frustrated. The last thing I want to do at this point is jump through hoops.

19

Received my RMA #, so hopefully once I receive the new Pixhawk this issue will be resolved.

20

Any updates on the replacement Pixhawk?