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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I have the latest ZTW Spider version according to Altitude Hobbies, who graciously took back the Maytechs that would not spin up (out of 8 could not get 6 to sync). In their view the Maytechs should have worked fine. Whatever. The 3DR ones are working with only the signal and ground wire attached, but are not very responsive compared to in the Y6B. 

The ESC's are currently in the tubes, but I think that's going to change and reside in the frame where there is good airflow. It's only 30-35F here so heat is not a problem, in summer that may not be the case, although many do without issue.

@Rob,

  I appreciate your input on all issues related to MR, and I'd like to think I did something wrong regarding the wiring, but I read every thread I could find on the subject and cannot find anything that would indicate incorrect wiring. I don't use O'Scopes and wouldn't know how to test an ESC anyway.

All I know is out of 8 brand new Maytech OPTO ST ESC's, independently using the rx they calibrated fine, no sync problems, throttled up nice. Once all six were connected to Pixhawk, there was horrible sync issues. I have no idea why, it doesn't make sense. Maybe there was one or more bad ESC's; seems unlikely more than 2 out of 8, but possible I guess. Throw in the 3DR ESC's, the copter flies.

Hopefully the ZTW Spiders will play nice with these KDE motors, and then the XRotors with adjustable timing will be interesting to try.

You have no proof of that. When 4 escs work perfectly on APM and the same 4 escs all experience extreme sync problems on pixhawk I would say pixhawk is the changing factor. Not the quality control of the escs. Something is off and no one seems to have it pinpointed yet. 

I've been following this conversation with great interest and can't wait to hear the results of your trip to see Craig at 3DR with your quad. It will be nice to see what you find.

I don't think you can make the assumption that because your ESCs worked fine with APM but not Pixhawk that something is wrong with Pixhawk.

Hopefully you can find the smoking gun so to speak and find an answer to the question.

Regards and good luck,

Nathaniel ~KD2DEY

The setup that was sent to Craig was mine, I don't know how you would describe the wiring on it a 'dogs breakfast'.  It is just one motor, one speed controller, and the power module.  When I sent my setup to Craig, he was exceedingly nice and responsive.  But he said they couldn't recreate my problem.

To check to make sure I'm not insane, I re-ran the test and, surprise, I can recreate the problem.  Here's the new video.

You are right on some points though, I really don't have any idea what I'm doing.  I _am_ monkeying around with test setups and flashing different firmwares.  I don't know what's actually different in the firmwares, and sorry, I don't have an oscilloscope.  I guess I'm just playing the lottery.  I wish there was someone, when presented with a reproducible problem, had the skills, experience and tools to find out what the issue was.  

Likewise I also don't think that because the ESCs worked fine with APM but not Pixhawk you can say its obviously the ESCs fault.

I also am a bit confused by the "dogs breakfast wiring". Having the ground for the ESC signal seems to be the only "error" in wiring I can think of. I have added a ground for the ESCs signal but still face the sync errors. I dont know how else you would wire my setup. The ESC power and ground is wired to the battery. The ESC signal and signal ground are connected to the pixhawk. The motor is connected to the other side of the ESC. How else could you wire it?

Absolutely, I agree it goes both ways. Looking forward to some results.

Regards,

Nathaniel ~KD2DEY

You couldn't by any chance post a copy of the log files from these tests, PM / No-PM? I'd like to see what's going on with board voltages etc.

Regards,

Nathaniel ~KD2DEY

Read this thread although you aren't using OPTO ESC; it still appears to apply:

http://multirotorforums.com/threads/kde-direct-xf-uas-esc-and-fligh...

For the 3D Robotics Pixhawk equipment, there is a hardware incompatibility of the Pixhawk to true, high-quality OPTO-isolated ESC circuitry. For OPTO-isolated ESC circuitry, the positive/negative control loop of the system must occur at each ESC port of the flight-controller, so that the circuitry is properly powered and kept separate from the full system. The Pixhawk hardware does not provide this, and rather, completes this loop through the ESC itself, grounding all ESCs to the central ground of the Power-Module. While this will work, it can introduce significant noise to the full system, as all ESCs are tied together to a central ground. For ESCs that are NOT OPTO-isolated, this will work and the ESCs will arm, but RF and electrical noise will pass through the system and can lead to instability issues or video noise.

To solve this, customers have provided great insight to the hardware and the current solution (special thanks to Rob, Freddie, and Quoc for their insight), which is to introduce a grounding-loop to the system. This allows the OPTO-isolated ESC circuitry to properly function, and the overall system will work excellent for flight. This is created by adding a negative and positive loop from the Power-Module to the Pixhawk, using one of the open ports of the "Main Out" section. In this regard, adding a jumper from the Power-Module direct to the "Main Out" section will provide the negative-ground loop - then all ESCs will properly arm. Please see the attached image to help explain the proper jumper arrangement.

Here you go.

Attachments:
I have asked Patrick at KDE to remove that post as it is pure gibberish. Unfortunately he has not done that and the misinformation persists. Please see this note in wiki:7 A Special note about KDE (and other) Opto Isolated ESCs http://copter.ardupilot.com/wiki/common-pixhawk-wiring-and-quick-st...

Thank you. 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.

I am not qualified to give a "scientific" explanation, only observations. In my case, I observed 8 Maytech OPTO ESC's refusing to spin up all 6 motors when connected to Pixhawk, but calibrated seemed fine individually. This is in no way confirming xoltri's, only that I spent hours in vain trying to figure out what was wrong.

If the ZTW Spiders do the same thing, what am I to believe? The 3DR ESC's work, but are not 100% on these motors. Maybe the timing is too low, I don't know. They are installed because I'm able to fly. However, there are times when they don't sync properly distinctly at low throttle, possible at higher throttle but my hearing may not be picking it up.

IIRC, I took the following diagram from an Arducopter instructional page. The only difference is I blanked out the ESC BEC portion. I see no reason why there would be power issues with this setup. Sometime this week I shall find out.

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