I believe I have a problem with my Pixhawk and was hoping for some help.  Also posted this on rcgroups.

The issue is that when my speed controllers are hooked up to the Pixhawk they exhibit a bad sync issue.  However when they are connected to my old APM (3.1) or just a receiver directly they do not exhibit these symptoms.  This has resulted in 4 crashes now until I just tonight narrowed down the issue to the Pixhawk.

Can anyone advise what is going on?  Here are the specs of my setup:

Afro 30A ESC's with SimonK firmware (have tried all versions, and made my own with various parameters)

Tiger MT2216-9 1100kv motors

4S 3700mah battery



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At hover my copter draws < 4A apiece on 4s. It is 3.1kg and using 14" props. I have a set of ZTW Spider 30A Opto (small version) and am contemplating trying them. I had Maytechs but could not get them to sync.

The motors are KDE 2814XF-515.

What do you think?

Spoke too soon. Didn't fix it, Motor No.6 still having issues.  New FC board, new motor, new ESC and even swapped Motor/ESC 5 for 6 still having issues on No.6!  Any ideas?

I didn't get as far as you; the sync issue was so bad on the bench I didn't bother putting it together.

Tomorrow I will be testing ZTW Spiders and make absolutely certain the wiring is correct. Odd though that 3DR ESC's work, sort of.

Hi All
It's not that I don't believe there is an issue here, but I need some of this faulty setup in front of me so I can get to the bottom of this.....

If anyone is willing to send their full setup to Sandiego (art Craig) or Ballarat Australia (Att Philip) that would help

It must be this issue, sync lost on Pixhawk. And it must be repeatable....

Please pm me and I will organise to get the tests done.

I can send mine back to you if you wish.  As per my latest youtube video the problem still exists.

xoltri, can you repeat your test, but hook ESC to a receiver supplied with 3.3v without any pixhawk involvement, also, can you open up that afro ESC and take a picture? 

I just bench tested my Y6 (Sky Hero Spy) with ZTW Spider OPTO 30a Small. All six motors spin and throttle up nice, no obvious indication of sync problems yet. I did ESC calibration independently with rx only, then did all-at-once with Pixhawk. Before doing all-at-once, motor #2 seemed to lag on throttle up, but afterwards all 6 sound and look good.

The Maytech OPTO I had would not spin up properly (had 8 ESC's to try), with one motor not spinning at all. I don't recall if it was always the same motor; put in just one 3DR ESC (after trying two other new Maytechs) and they all worked, so swapped out all 6. Very odd to say the least.

Now I'll put it all together and see what happens with the Spiders. 

For power, I have the PM connected to Pixhawk and a HobbyWing UBEC 5v is connected to #7 on the rail. I've seen it suggested to loop the PM to the UBEC, but  don't see the logic in that.   

Hi Philip,

If I cant get it fixed then I will send it.   It is definitely repeatable, so much so I don't trust it enough to get in the air.

I. will let you know how the test go.  I am thinking/hoping that it is the PDB but you never know.

Artem, not sure what 3.3v would accomplish.  It already works fine if I 1. Disconnect the power module from the Pixhawk (or remove it entirely) or 2. Control the motor directly sans Pixhawk with the 5V BEC on the receiver. 

But sure, I can take the shrink off of the Afro and take a photo of both sides of the board.

I am wondering if this is 3.3v pwm having issues with some afros... 

Ah, well since it works on the 5V BEC, even through the Pixhawk, I don't think that's the problem.  

Now I'm no electrical engineer, my day job is as a computer admin.  But my best guess, at least in my specific situation, is that it is a ground loop introducing noise.  One ground goes via the power module to the Pixhawk over the 6 pin connector, and the other ground is via the power module to the power distribution board.  If I remove this alleged loop by either disconnecting the 6 pin connector to the Pixhawk, or by removing the power module entirely, or by not using the Pixhawk at all, the problem goes away.  Or, as is my solution now, replacing my Afro ESC's with the 3DR branded ones.  Maybe the problem combination is that the Afro's can't handle the alleged ground loop noise as well as the 3DR ESC's can.  Or maybe the 3DR ESC's are wired differently to eliminate this noise.  But really I don't have the tools, skills, or experience to know what the problem is for sure.  All I can do is post my observations.

Back in the day my hobby was car audio.  On my first install I experienced a bad ground loop resulting in hearing the RPM of the engine via the alternator through all of the speakers because the head unit was grounded to the front of the car, while the amps were grounded to the rear of the car (ground loop).  The fix was to run the ground for the head unit all the way to the back of the car, and the problem was solved.  In the Pixhawk, I wonder if I tied the two ground wires from the 6 pin connector to the ground of the power distribution board if that would fix the problem.  But I don't know enough to be sure, and I'm not brave enough to try.

Here is an update to my situation. 

I have replaced my Afro 30a's with HK blueseries 30a's and my sync issue seems to be fixed. 

This video was with the Afros, just raising the throttle caused major sync issues. 


This video is with the Blueseries. I do hear a high pitched whine which I have never heard before. But the sync issues seem fixed even when using throttle hold to go from 0 to 100% throttle. (note I tested these one motor at a time but they all work the same.)


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