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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It must provide some 5v out at the rail though right? Because it powers your RX off that same rail?

The RX is on its own rail
You should NEVER run anything other than your RX off that rail

Hey guys,

even in Germany we experience the same problems.

I took the stuff of my old and heavy frame (pixhawk, KISS 18A, Tigermotor 3508-16 700KV) and mounted it on to my new, lightweight frame.

Everything is the same except for: shorter motor cables, longer batterie cables and capacitors to compensate for the longer batterie cables. Also, I swapped one ESC that looked suspicious. 

BTW: on the old frame everything worked just perfect. 

For the first test I ran the Pixhawk with the settings of the old frame: no problems; well one motor was turning in the wrong direction. Soldered it and thought everything should be fine.

So I ran all the calibrations for the new frame.

After that one motor started shaking like crazy, which reminded me of the motor calibration which I forgot.

Did that...

While running in motor calibration mode everything was fine - no problems whatsoever.

Entered "live" mode: each and every motor is shaking like crazy. Can't speed up the motors - maybe reach 25% of throttle.

After that I did a ton of resets, firmware updates, changes in the FC (Thr_min etc.) and cable checks: Nothing helps!

Any suggestions?



Can you please check the cable between the power module and the Pixhawk to make sure that all of the wires have continuity and that ground is continuous through that cable.

Then remove the connection from the servo rail to the ESC and verify that there is continuity from the ground pins on the servo rail back to the ground connection to the battery.



I'm confident now to say the ZTW Spider 30A OPTO Small ESC's are performing well.  After 6 flights no hint of sync issues. 

Now on to tuning and all that good stuff.

Oh happy day.

That's what I told you, but they do seam to run hot, unless they are 2x max current, than they run moderately warm. BTW, are you using new slim spiders? 

Final update from me on this situation. My HK blueseries escs are working well. I have put about an hour of flight on them now with no issues. No heat from the escs or heat from the motors. All seems good.  

I did drop my Afro 30a's off with Craig from 3dr this past weekend. Hes going to see if he can get them to lose sync on the bench. I was too impatient to bring my malfunctioning copter down to san diego with the afros still mounted. Hopefully they can recreate the problem and get to the bottom of this. 


Big news - problem solved!

Here the story and some thoughts on the problem (on my problem... I don´t think that I found the overall solution even though I sure hope so).

When I assembled the new frame with the "old" components I wanted to run a quick test. So I left the software settings on the Pix as they were (no new calibration!)...AND I used cable ties to DIRECTLY mount the pix on the frame. I wasn´t quite happy to mount the Pix without vibration dampening but I just wanted to find out whether the motors would spin and if so in which directions. Everything worked perfectly - so I finished the copter.

Being sure I wouldn't have to change anything anymore I then used the dampening pads to finally mount the Pix. Due to some space issues I used only two pads (worked just fine beforehand) which I placed relatively close to each other.

Having finished the copter like this it would always started shaking like crazy when increasing the RPM from minimum idle to ....whatever!!! 

It took me a few thoughts to figure out what I did wrong or what could be the reason for this problem...

Here we go:

Having the pads so close together made the Pix a seesaw. It would move too much and swing up easily. This in combination with a low starting RPM of the motors and a huge and abrupt increase in RPM when accelerating caused the Pix to swing up. When the pix recognizes these torque impacts it tries to compensate for them and the whole systems swings up immediately.

Interestingly enough, some people here in Germany - and I believe that's true for the U.S. community, too - reported that they could solve their "sync issues" by increasing the "minimum motor RPM". Now that absolutely makes sense to me: The higher the starting RPM is the lower is the step to the ... let´s call it "reguar idle" of the motors, when accelerating the first step with the radio....the RPM gap is smaller and so the torque impulse on the frame is lower and the whole system might not swing up ... if you're lucky.

I tested my "hypothesis" a few times and I can recreate the problem (or make it disappear) at any time, simply by applying a little pressure on the Pix-body with my thumb.

No thumb (just foam pads) -> shaking like crazy!

Thumb engaged -> no problem!

I don´t know if that works for you guys but it is true for me and might be worth trying.

Wish you all the best of luck!


Did AT today, went well although not sure about the results yet.

So later I decided to take her up later. Temperature outside was about 25 degF and I've heard it's good to acclimate the copter to ambient conditions so I let it sit for about 15 minutes. Then armed it....barometer glitch. Ok, shut down and restarted.....armed.....everything good until.....oh oh, sync problems are back, so I thought. Here's what it sounded like:


I recalibrated the ESC's to no avail, then brought it inside for ~20 minutes. The motors were considerably more difficult to spin by hand. Over time they spun freely as normal, so I tried again:


Conclusion: Cold temperatures affect my copter's performance until the motors warm up.

Ok motor heads, please watch the takeoff in this video and tell me if you think it is a sync issue, a motor issue, or no issue.

The rest of the video is just testing PID settings in Loiter.

Also, at high and full throttle, there is a "miss". It flew at 24 m/s, but to me it sounds like it isn't quite right. So basically, to my ears it occurs at low throttle and wide open throttle.


I should add that doing all-at-once ESC calibration, the motors throttle up nice and sound good in that mode, but once re-arming, they don't sound good.

See my post at http://diydrones.com/group/arducopter-octaquad-x8-owners

HobbyWing is my choice of ESC now.

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