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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Are you twisting both the power cables and the signal wires? 

My particular build is a Tarot FY680. This build will require about 35mm extensions on the signal wires, and both the power wires and signal wires run inside the carbon tube arms together. Lots of length for them to couple, unfortunately.

It was mentioned in a prior post using cat5 cable for the signal wires but I couldn't figure out if they meant to strip a single twisted pair out of the cable or if they used the entire intact cable. 

Someone should make opto isolated ESCs with fiber optic signal wires so the LED plugs into the flight controller and the photo transistor is on the esc board. 

Is there a simple, external way to boost the signal from the pixhawk to 5V before sending it to the ESC?

II am using Afro slims which have the same hardware as afro 30a and the same f/w but do not have BEC so no wires and my installation is inside the 16mm tubes.  So no extensions at all just twisted signal and gnd. 

Allright new update... As mentioned, I had some luck getting the thing off the ground after I set RC_SPEED to 100...
After that, I configured my Auto Tune.
I lifted off the ground, and got it to a steady position, in Alt Hold mode, switched on the Autotune and the thing twisted straight into the ground, crash!
My own theory is that as soon as I switch on autotune, pixhawk ignores the RC_SPEED 100 and goes into some standard mode, and back to original RC_SPEED, which I think was 380.

Here is the video:


That was painful to watch! So sorry to see that. :(

Are you positive it wasn't magnetic interference from the power wires caused by the high current demands of auto tune? 

Hi Artem, I am flying since last we pixhawk with AfroSlim BlHeli flased EScs, and flipped the quad in stabilize mode after a few minutes of flight on 3 occasions, the same day.... Would you mind sharing the best setup in BlHeli suite for these Slim 20A ESCs please? It looks like a sync problem, and after several trials on setting them up on BLHeli, I still can't get it wright....! Thanks for your help on this one, as I am getting frustrated, can't getting the bird properly in the air... Cheers for your help if I may...

There is no way that can be caused due to magnetic field interference, it was flying fine isn't it.

A bad mag heading would cause a fly away or a ekf compass error....this definitely looks like a sync issue. Logs please   

I wish I had a log on this, but it was not enabled :(

Now I have just got some new Tarot arms, and new ESC ZTW Spider series 30A with SimonK


If it does the same thing with new ESC and arms, I'am thinking about having a bonfire with at my local Danish RC-Club and burn the freaking PHawk before if costs me any more money... :D

Can anyone confirm or deny that RC_SPEED goes "back" to standard (380 Hz as I remember was standard) when PixHawk is set into AutoTune mode???

I am using simonk on them the last time I updated those was in may/june 2014 on them with timing high and pwm_comp on. I suggest you check your solder joints. I once had an ESC on a miniquad loose sync burn itself and the motor because I used a different type of solder on one of the motor leads (ran out of regular solder). I never use bullet connections as those introduce additional 6 failure points per motor (3 additional solder joints + 3 mechanical connections), heck those! Often times people complain of the motor loosing sync with pixhawk, while they haven't done basic sync testing on the bench with a simple servo tester/Rx. test each motor/esc pair. AC logs wil clearly show which motor is failing (loosing sync). If it is the same motor each time the reason is most likely mechanical - bad ESC/bad motor or more likely bad solder joint/ sometimes when using long bolts to mount motors bolts will touch windings damaging insulation and upsetting timing. 

good luck! 

Thanks ever so much,, I will rebuild it from scratch I think, it'll be

Hi Artem, I am rebuilding the copter and tempting to setup the Simonk firmware on my slim20A afro ESC. One question though; would you remember which firmware you took to flash your EScs, please? Should I go for the Afro OR Afro NFET or Afro2 please? This is from the KKmulticopter flash tool repository! Thanks again for your help and support so I do it good this time around! ;) Cheers

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