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Pixhawk 680 Quad falling from sky

Posted by David Tipping on September 5, 2015 at 3:22am

Hi – can I request some help with my home built 680 Pixhawk controlled quad please. Sorry if I’m not in the correct place in this forum.

The craft has done several autotunes and in some ways seems to fly ok however on most flights, possibly when yawing, it will over balance and being unable to recover, hits the floor. I am flying low altitude to avoid damage and have seen it recover once.

I am not familiar with analysing logs beyond the obvious – GPS, voltage, current, altitude info etc. and would really appreciate someone with more experience taking a look at this short log please.

Something is obviously going wrong around the 10300 line mark. The later error and failsafe are just about the radio being turned off.

Here are the PID settings:

Thanks in advance

David :-)

2015-08-30 17-29-00.bin

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Replies

Rick Steer September 19, 2015 at 11:41am

Hi, are you grounding the ESC signal wires?
- David Tipping > Rick Steer September 19, 2015 at 12:14pm
  
  Hi - yes, but only one of them.
  
  This is the ESC I'm using and only 1 of the 4 ESC's has earth and +5
  - Rick Steer > David Tipping September 19, 2015 at 1:53pm
    
    It could be that your motors are going out of sync.
    
    Connecting the Ground Wire
    
    An electric signal is defined as the deviation from a nominal zero-value. For normal signals this reference is ground (GND). Therefore just one wire is never enough to transmit a signal - it always needs a reference (on differential signals, the reference is established by the difference). A wiring setup not in need of a ground reference doesn't exist, and if the path the current has to take to “return” is much longer than the signal wire, complex electromagnetic effects can come into play. The image below shows how noisy the signal becomes if GND is not connected.
    
    I know that 3DR's 4in1 also only uses a single ground but lower KV motors have been known to have sync problems on Pixhawk unless each individual signal wire is grounded.
    - Vital Belikov > Rick Steer September 19, 2015 at 1:57pm
      
      He has each individual signal wire grounded. It does not matter where wires are connected - on esc or on pixhawk. And it not looks like out of sync. Too fast recovery.
      
      Of course it would be good to check that there is no noise on signal.
小不点 September 19, 2015 at 8:40am

直接焊接,过热会不会溶化了呢?
Vital Belikov September 16, 2015 at 1:56pm

It looks like hardware problem for me when viewing your log. FC controlled banking, but copter went to a different side. Same with pitch.
Does all your motors spin good? Al escs are calibrated? And so on...

diydrones_quad_crash.png
- David Tipping > Vital Belikov September 17, 2015 at 2:12am
  
  Thanks for your assesment. I noticed a dry solder joint on one of the pair of parallel batteries i power this craft with so it is possible this is the issue. I have repaired the joint but not had oppertunity to test it yet.
  
  My batteries are rated at 60C so that should be plenty of power even if one fails to supply, however maybe the sudden dropout in supply is disruption enough - what do you think?
  
  David
  - Vital Belikov > David Tipping September 17, 2015 at 3:22am
    
    There shouldn't be dropout if one battery disconnects. It's a pity that there is no battery and current in this log.
    
    But as we can see from screen that i attached - first thing what FC was done: increased throttle to almost maximum. Then copter starts to rotate in all axis, apm increases throttle to maximum, but with no luck. There is no power from motors. And it's falling.
    
    May be your battery disconnected at start? If it is esc protection - one motor shuts off due lack of voltage and can cause such a thing.
    
    Have you charged your batteries? May be one is fully discharged?
    - David Tipping > Vital Belikov September 17, 2015 at 10:22am
      
      Hi - batteries have less than 15 short flights on them so this should not be the issue. The quad is recently completed and has never flown properly. Every time I get a short successful flight I think it is sorted and purchase a new undercarriage. When I come to fly it with new bits it does this, crashes and breaks another set of legs.
      
      I tried another flight today (on long soft grass) lasting 7 mins and it faltered at least 3 times at about: 15:53:52, 15:55:18 and 15:57:55 - fortunately it did not hit the ground. Overall the flight seemed to go well and the craft is responsive.
      
      This is my first self-built copter and I am making it up as I go so I may have something obvious going on. It has been stable enough to have auto-tuned.
      
      I have posted a zipped log file of my flight today as opposed to the bin file, I was not aware that bin files did not contain all attribute information.
      
      I would really appreciate any assistance I can get
      
      Many thanks
      
      David :-)
      
      2015-09-17 15-51-25.zip
      - Vital Belikov > David Tipping September 18, 2015 at 12:26am
        
        I was trying to say: if batteries was in parallel they will be discharged to a same amount. If one battery was disconnected due to soldering issues - it will be visible, that one battery is discharged more than another.
        
        Bin files do contain all data. In fact bin file is downloaded from your vehicle, and then converted to log. So there is more or same data in bin a-priory.
        
        I reviewed your log. Yes, there was three strange things at 15:53:52, 15:55:18 and 15:57:55. In last copter banked harder and first two were more smooth.
        It is interesting that in first two glitches copter was banking only on roll axis. And one time to left, second time to right.
        
        This should say that there is no problem with concrete motor.
        
        But looking at copter behavior except those three moments I can say that it's tuned ok. It definitely can fly. And those three moments are looking as hardware issues. But i do not believe that it is battery or motor\esc defects. One thing to inspect - power distribution from battery to all escs. Maybe there is cold solder too?
        
        Can you post video of your flight?