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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Please note this comment at RCGroups:


Santiago (3drobotics)
Dec 03 02:16 PM

Hey Jonathan,

Thank you for contacting Technical Support.
Afro esc's do have sync issues because of the rated 1kHz input. The pixhawk outputs at 400Hz and is what to look for when searching for esc's. Officially I can only recommend our 20 amp simon-k esc's. I highly doubt you need higher but tell me a little more about your build and let me check if there is anything that might help with the sync issues.

Best Regards,
[Technical Support Engineer]

Ok, so what does that mean? Is there are parameter setting in MP that could be changed? The ZTW Spider is rated at 600hz. Should I expect problems?

It's really strange that it happens immediately for you but not for 3DR when they tested.

Out of interest, did you ship the LIPO with the Pixhawk/motor/ESC?  I'm wondering if there's some strange voltage sag that happens when you flatten the throttle.

No, I didn't, but it happens both with my 2200kv motor on a 3S 2200mah lipo, as well as on my 1100kv motor on a 4S 3700mah lipo, so I doubt it is related to the battery.

>>>Does that also mean the UBEC can be connected to the 'Aux Out' pins rather than the 'Main Out'? That's what I understood to be the case months ago.

You can connect the BEC anywhere along the servo rail.  All the pins on the +5 rail are connected to each other and all the pins on the ground rail are connected to each other.

That is really curious.  I don't see any difference between the way you had it set up and the way I had it set up here.  I should have taken a video...Anyway, now I am curious about the interaction with the power module.  When you took the power module out of the circuit, what were you powering the Pixhawk with?

Hi All, I have been watching this thread and am amazed by the venom from some.  Aren't we all trying to find a solution.

before I get into a rant:

I have a sync issue with my 3DR BUILT,  RTF, STOCK, Y6B running anything higher than 3.1.5 firmware.  It seems to be fine running 3.1 but on 3.2 rc2 thru 14 it keeps losing sync on motor 6.  I have change the ESC and mar and all associated cabling to this motor with no change.

Original wiring was done by 3DR wit all GND/Power/Signal wires connected to the 3DR power distro board and then all signal wires connected to Pixhawk and one set of power/grown connected to Motor6 Port.  I have checked continuity and resistance on all connections and they are good.

COme to think of it I will try moving the power/Ground connection to another free port like Motor7 as it occurs to me that this is the only difference between the intermittently faulty motor position and the others.

Another symptom I have observed is that idle speed seems to turn motors fine on first arming.  Once I throttle down motors do not spin (Not disarming) but when I ramp up throttle motors jump to about 30% speed.  Once I raise throttle to above 30% they track fine but Motor6 will lose sync.

This is all original 3DR parts and wiring so hopefully that should avoid any comments about spaghetti wiring, mixing grounds etc.

I have been flying a small250 size quad with 3.2 for a while testing before I tried it on the Y6B and it has been fine with all types of ESC's. If I go back to 3.1 then I have no problems.

HELP!!!  I have already pulled my machine apart several times and changed/replaced and swapped ESC's and Motors.

I'm either misremembering, or there was somebody else who sent it to Craig that you are not aware of.

Just Xoltri

Just to be extremely clear to users: Other than the RC Input pins.  On that one, the ground pin is not connected to the 5V rail directly.

These PWM ratings are very confusing and/or misleading.  It is physically impossible to drive a 2000uS PWM signal at more than 490hz.  As in: basic laws of the universe impossible.  

So any ESC that claims to take higher inputs is suspect.  It is possible they can go faster, with a shrunk PWM window of less than 2000uS.  But this is not clear at all.  

IMO, ESC's that market high refresh rates are suspect of selling snake oil.  

Well, possibly success but I will need to test further and see if I can make the fault reappear.

I changed the Power/Ground connection from the power bistro board to a motor output port (Motor7/RC7) that has no signal wire connected.  (Y6 using Motors 1 thru 6) and the intermittent loss of sync on Motor6 seems to have gone.  At the very least it has reduced the frequency.  It used to happen on every bench test within a minute of spinning up the motors.

Logs look the same as always with clean and consistent outputs to all motors, all relative to throttle and attitude as expected. I will recharge batteries and run them through again on the bench.  I used to get Motor6 to lose sync every time I spun up the motors, this is the first time I have been able to get through an entire battery without an issue on 3.2 on my Y6B.

What concerns me is that I have been running 3.2/Pixhawk on my 250 quad for a while without any issues and that I know that other people do not have this issue with exactly the same gear.

I thought it was a motor or ESC issue but I have replaced and swapped position of motors and ESC's and the problem remained the same.  I ruled out faulty Pixhawk as I could eliminate the issue all together buy reverting to 3.1.x firmware.  This is still the case.

I spoke to Santiago today and cleared up his misunderstanding on the ESC update frequency.

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