Crash with x8 after low battery warning! battery still 40%

Discussion in 'Cinestar 8' started by Jason Smoker, May 15, 2015.

  1. Jason Smoker

    Jason Smoker Active Member

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    Just had a crash after my low battery warning light went on. It suddenly took off up like 80meters and then decided earth was better place to be.

    Can someone tell me what the hell happened?

    thanks peeps

    Jason
     

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  2. Jason Smoker

    Jason Smoker Active Member

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    can someone please post the gpx file on mircokopter forum I have no idea how to upload the file there.

    Thanks
     
  3. Dave King

    Dave King Well-Known Member

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    Jason you got a low battery warning just because of the high throttle position and load of the copter when you had altitude hold off. Your stick value in manual mode indicate a high level of throttle. It's not uncommon to hear that with of energy in the batteries when the copter reaches the 22 volt mark. In these situations sometimes the voltage very quickly will spikes below your undervoltage setting. Again this is nothing that's uncommon. Especially if your battery voltage sags like mine do. My battery voltage runs in the 21.8 to 21.6 range for quite some time with plenty of energy left. When its at that point if I have to give it a good amount of throttle the voltage will spike below my undervoltage level and I hear MS MK give me the warning. This does bring up something that you should look at which is are your motors undersized for your pay load? What is your hover gas value with altitude hold off? I'm thinking that it might be 65% of higher which is why your stick throttle was so high with AH off.

    As for the crash it appears that your were flying around a lot of metal, or interference that caused you to lose GPX fix quite a number of times. It starts at line 779 and really doesn't recover for it until the last recorded value at 857. That's about 45 seconds of logging that indicate to me that you had GPS fix issues. Did you hear Ms MK say "GPS Fix"? The datalogging shows that it spoke the "GPS FIX" error many times. Anytime you hear that you must immediately turn GPS off. When there are distruptions to the GPS signal such as magnetic influence the MK flight controller has been known to freak out and do sudden things it should not be doing. Ask me how I know?
     
  4. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Jason: It appears that you were flying in the city and it is highly likely you were near either cell phone towers or microwave links (I'm speculating based on the Google Earth view of your flight and it's impossible to see where the cell phone towers/microwave links might be. It's also hard to determine the heights of the buildings to see if that in some way would interfere with the GPS. The receiver shows 16 satellites, but, as Dave says, it was losing GPS fix a number of times before the crash. Also, there is a strong correlation between the low battery alarm and the GPS_FIX error status -- the GPS_FIX error status only ever happens when the low battery alarm is active. I'm not quite sure what to make of that, but I suspect it's telling us something.

    The curious thing is that, as you were not using Position Hold at all, the autopilot was not generating any stick inputs, so apart from Dave's experiences, it is not clear at all why losing GPS fix would interfere with the flight.

    That said, with all that possible radio frequency interference in the city environment it's conceivable that might have been a problem.

    Andy.
     
  5. Dave King

    Dave King Well-Known Member

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    I've seen it happen to me about a handful of times where I am flying manually with no PH and the copter does something it shouldn't because of a GPX fix issue. This doesn't make sense and the only thing I can come up with are two things. One something on the flight control board is sensitive to magnetic fields or two when the Navigation board experiences a GPX fix issue something happens between the communication buses between the NAV and FCB that causes the FCB to freak out. That's my theory. Jason has the upgraded GPS board and I seriously doubt that there was any issue with tall buildings affecting the signal as you would see a drop off in satallites which there is no indication of here. My suspension is that the issue is related to magnetic interferences from another exterior source.
     
  6. Steve Maller

    Steve Maller UAV Grief Counselor

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    I took a look at the GPX file, and I'd suggest y'all reviewing it to see if you see what I see with the "STICKS" window and the "OSD" window open in the MK_GPX tool. At like #834 or so, I see the copter at 80m or so, and pulling nearly 2000W (which is a lot). I also see that it's quite possible that the copter was seriously out of balance based on the current draws of the various motors. But after like #834, I see some significant deflections of the control sticks (including the throttle). The copter was not in AH or PH, so it was being flown that way by the operator. There are a number of serious pitch and roll angles in excess of 60°, too. It is impossible to say whether there were physical forces at work (serious wind draft, obstacle, or balance issue), but I would venture to say that this was not at all related to EMI or GPS problems. Sadly, we may never know exactly what the cause was, but what I see in the GPX log indicates a high probability that this was a manual control issue.
     
  7. Dave King

    Dave King Well-Known Member

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    I have had a couple near death experiences where my stick controls didn't do much of anything no matter of stick position. If you are in mode 3 you can't do 60 degree rolls (at least by stick commands). So either the recorded data is flawed or the FCB was flipping out big time or it was doing wacky things that makes the X8 flip out. I am still not a firm believer in the X8 with MK electronics although I know it can work if all components are matched up just right like Steve's rig.

    When I had issues with the MK responding to stick commands in flight Holger told me that he suspected that when I calibrated the gyro (stick upper left) the copter was yawing on the ground which he said can cause some serious issues. This can cause both FCB in manual mode and PH issues. Back at that time I had my 8 bit alexmos where the copter would yaw back and forth a little on the ground. He made it perfectly clear to me that the copter has to be dead stills when calibrating the gyro. After Holger told me that tip I made sure I properly calibrated the gyro with the copter dead still and I never had an issue like the one I explained (manual flight issues) again. Sometimes I have a very hard time doing that in high wind conditions to get the copter dead still even for a 2 second period (sometimes it takes me 20 minutes of just sitting there waiting for the wind to calm down). But I make sure that I do not fly until I can calibrate the gyro with the copter being dead still.

    Since then I have had GPX fix issues in mid flight "IN" PH mode that caused the copter to do funny things. A quick switch to off for PH fixed those issues though.
     
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  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Steve: I noticed some of those extreme pilot inputs (throttle back to zero, yaw full left), but wondered whether that was happening after the copter started to show signs of being out of control. You really see them if you use GPXTOOL to look at the stick display and the OSD as you say. But why the GPX-FIX errors every time the LOWBAT status?

    Dave: GPS is operating up at 1575 Mhz and 1227 Mhz frequencies -- what have you seen to suggest these radio frequencies are subject to magnetic interference as opposed to radio frequency interference.

    Also, one normally recalibrates the ACC only once -- and indeed with the copter absolutely horizontal and motionless. You certainly don't need or want to recal the ACC before each flight.

    You *do* recalibrate the gyros before each flight but definitely not the ACC.

    Certainly if you are in PH, and the GPS has issues it will most certainly cause "funny things" -- the copter is trying to maintain its position based on GPS coordinates -- if those suddenly change (because of GPS issues) -- the copter/FC/NC will suddenly think that the copter is in the wrong place and it will move to correct that.

    Andy.
     
  9. Jason Smoker

    Jason Smoker Active Member

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    Hey guys thanks for looking just an update I flew my flat 8 there early in the day with no issues. The wind picked up so i decided to fly the x8. Dave this machine isn't underpowered this is a Quadrocopter kit and was flying a radian 3axis gimbal with a cannon 5d so it has plenty of power both rigs! The only difference with electronics is that the x8 has the new gps v3.

    All I know was that after I saw the low battery light it took off really fast with no control the last 30 secs of flight was me trying to getting back down to earth with injuring anyone.

    Andy yes this was in the city so lots of metallic interference I have my compass effect set to zero so I hopefully don't get any wired effects.

    I dont remember high putting the throttle stick high I wanted it to come down not up 80m in the air. Also I wasn't using Gps so hmm any other ideas this rig is grounded until I can sort it out!


    The only other thing I can think of is that i added the longer anti-vibration axiels recently maybe it acted like a pendulum in the stronger winds?
     
  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Jason: Have a look at the GPX file using MK_GPXTOOL and open up the Sticks window. Look at rows 779 onwards and you'll see the blue squares -- those are your stick inputs. It certainly looks like you were wrestling with the aircraft -- my guess is that it shot up, so you chopped the throttle way back, so it then decelerated and started to descend and, to kill the (probably alarming) descent rate, you goosed the throttle pretty high...

    Andy.
     
  11. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Oh...and also, I'm not talking about *magnetic* interference...I'm talking about radio frequency interference....for which there will be numerous sources in a city.

    Andy.
     
  12. Ozkan Erden

    Ozkan Erden Distributor

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    Jason,

    Can you check with MK Tools what are your settings under MISC tab?

    Can you post a screenshot like this?

    [​IMG]

    I'm wondering if this is related with CH / Autoland voltage and emergency gas /time settings. We would see it in the logs but I couldn't notice it on the logs anything about this. Just to check.
     
  13. Jason Smoker

    Jason Smoker Active Member

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    Yes I will do but I won't be until Monday
     
  14. Dave King

    Dave King Well-Known Member

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    Andy

    Sorry for the confusion I don't want to add to it. I did mean to say gyro calibration not ACC. I will reedit my original post with the correct terminology. As for magnetic interference as opposed to RF its nothing more than a feeling based upon flying two different rigs at the same place. I have flown both my Wookong rig and my MK rig at the same place with nobody around away from a cell phone tower and the MK reacted in a way where I was getting magnetic interference with the copter yawing a little (out of PH mode) here and there and the wookong being completely stable. I would have to do a back to back comparison, same day, both rigs test to verify but its just a hunch. I don't want to make it sound like this is a big issue because out of 3000 flights I have seen this happen less than 10 times.
     
  15. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Thanks for clarifying the ACC/gyro issue, Dave.

    As to the way the different copter's react, and based on what you say (low EMI/RFI environment) that *suggests* (but is not conclusive) that either the copters themselves are the source of the EMI, or the compasses on the copters are reacting differently, or the flight controllers are using different algorithms for yaw stability (I know the MK has the option to use the compass). Puzzling, isn't it?

    Andy.
     
  16. Jason Smoker

    Jason Smoker Active Member

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    he is the screen shot of my misc settings for people interested. I am going with " Steves idea" that the copter was out of balance. After looking the motor currents.Even though I did i quick check before take off. I thinking my Pan balance may way off due to the extended axial posts i recently installed http://forum.freeflysystems.com/ind...-offs-for-vibration-dampening.6288/#post-6008. Hmm anyway onto re-building this rig.

    i didnt check that one but the foward and rear balance seemed fine.
     

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  17. Jason Smoker

    Jason Smoker Active Member

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    By the way are these settings ok?
     
  18. Ozkan Erden

    Ozkan Erden Distributor

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    The reason why you are getting lots of undervoltage error is, your undervoltage setting is high. The battery under load will be fine with 21.6V but your copter is giving warning to you with your settings.

    Your CH voltage is also high, I need to check the log file again if the copter triggered CH and see what happened after 60 seconds you got a warning. Because your CH time is set to 60 seconds.
     
  19. Dave King

    Dave King Well-Known Member

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    What do the numbers 32, 33, and 34 mean? I put in actual numbers like 216 for my values. That would explain why its going up if its trying to go into come home. IF its going into come home and the GPX fix is not there that could be why all the issues were taking place. I always set my come home voltage really low like 19V as I don't want it coming home unless I am telling it to or unless its going into fail safe.
     
  20. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Numbers such as 32, 33, or 34 are the volts per cell x 10. E.g. 32 is 3.2 volts per cell.
    If you put in a number like 216, then that will be interpreted by the firmware 21.6v -- which is the total battery voltage for 6S.

    Andy.
     

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