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Pixhawk causing motor sync issues.

Posted by xoltri on March 10, 2014 at 10:50pm

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

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

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

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Replies

    • Ron LaBorde > Easy September 11, 2015 at 7:59pm

      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? 

  • xoltri August 27, 2015 at 7:38am

    Simon Kirby responded to my youtube video with the following:

    Hi, all! It turns out that the pixhawk (http://3drobotics.com/wp-content/uploads/2014/02/px4fmuv2.4.3_schem...) uses TXS0108 buffers on the motor PWM outputs. This is a bidirectional buffer with edge accelerators, which in combination with the 220R in series with its output, means that the holding impedance of a static output signal is significantly less than with some more simple (no ESD protection) flight controllers. This means that other noise sources such as from the power wires may more easily induce current in the signal wire, and the 3.3V signal margins versus the 5V ESC MCU may cause some interesting oscillations (as seen here). You may find that simply twisting all of PWM signal wires (with their ground conductor) will reduce the inductance from the power wires enough to solve the problem. The worst case would be non-twisted power wires running beside non-twisted signal wires for long distances (so this problem may also happen more easily on larger crafts). The problem will exist regardless of software (other than its impact on current), but ESCs with ATmega8 (as opposed to ATmega8A) seem to have lower I/O transition voltages and so leave more margin for noise. The best solution would probably be a fully opto-isolated signal input ESC (not currently available for the Afro) that can deal with noise in the signal (by ignoring the offset applied to both the PWM and GND wires). Not to be confused with "OPTO" that merely means no BEC is present. These can be difficult to find sometimes because of this. Please let me know if this does or does not fix the issue for you!

    Just wanted to post this so the info didn't get lost.

    • Ron LaBorde > xoltri September 5, 2015 at 7:18pm

      So basically this confirms that the combination of Afro ESC and Pixhawk is a no-go due to hardware incompatibility? The Afros can work with other flight controllers, and the pixhawk can work with other ESCs, but combining the two is a crash waiting to happen unless you use twisted pairs for the power wires and the signal/ground wires?

      Are there any 30A ESCs available that can be flashed through the servo connector like the Afros, but are not susceptible to noise?

      Would it be practical to modify Afro ESCs to include something like this?

      http://www.amazon.com/2-54mm-Pitch-Mounting-Photo-Coupler/dp/B00BJH...

      Or would it just be better to seek out new ESCs? I don't want to risk a crash, and I don't want to twist my wires as that would require more wire length to compensate for the twist, and add weight.

      • Artem > Ron LaBorde September 5, 2015 at 7:40pm

        I am flying pichawk with afro slims (essentially afro30a)  for more than year now without ever experiencig sync issues. Just make sure you have latest SK on them or BLheli runs both. About 6month those were flown with 380kv motors and 1555 props on 4s, and about 6month the same ESCs been moved to a different copter with 2216 800kv motors. But yea, I always twist my cables, that's just a general practice to prevent noise from ESCs radiating off the signal wire... 

        • FPV Cambodia > Artem September 14, 2015 at 11:58pm

          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...

          • Artem > FPV Cambodia September 15, 2015 at 10:19am

            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! 

            • FPV Cambodia > Artem September 21, 2015 at 12:53am

              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

              • Artem > FPV Cambodia September 21, 2015 at 10:09am

                3702909746?profile=original

                • FPV Cambodia > Artem October 7, 2015 at 5:00am

                  Hi Artem, I rebuilt the copter with NEW Slim 20 ESC with SimonkFirmware but still have a motor not sync on throttle start, it disappears on recalibrating the ESCs on the PIxhawk each time i arm, which is not recomforting.... I was studying the evening the KKflashtool to set the High Timing and PWM_comp as you suggested, but seriously, after few hours, I cannot find any support out there as to how to set these parameters while reflashing the ESCs with latest SimonK! Harrrr!? You've been kind enough so far with patience towards this issue; but here seriously, I would need you guidance understand which Software you are using for flashing SimonK atmel ESCs in order to set these parameters on the ESC and save them!?!? I am almost there Artem. Tks for your help and support; always much appreciated....

                  • OG > FPV Cambodia October 7, 2015 at 5:11am

                    ditch the NEW Slim 20 ESC with Simonk Firmware ! you need BL heli compatible ESC with pix Hawk !!

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