2nd Crash in 6 months

Discussion in 'Cinestar 8' started by David N Atkisson, Apr 18, 2013.

  1. Steve Maller

    Steve Maller UAV Grief Counselor

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    For those who care to watch, here is a replaying of the final 10 seconds or so of the flight using the MKGPX tool. It's essential even for "normal" flights as a training and diagnostic tool. But the ability to use it like a debugger like this is how several of us were able to piece together what happened.

     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Dave:
    I'm don't think that the evidence in this case really does implicate the compass. Bear in mind that the compass data is primarily used for yaw/heading stability -- you can even disable the compass' effect entirely, of course, and still fly the copter quite normally (provided that you don't want to use waypoints or position hold).

    Certainly, it is a good practice to calibrate at each new location.

    The GPS Loss warning simply means that the number of GPS satellites being received dropped below the threshold number you set in MK Tool. Again, unless you're using CH that's not critical. Also, it's worth noting that the number of GPS satellites immediately recovered in after the GPS Lost messages -- and at no time was less than 7 satellites -- more than enough for a 3D fix.

    So, bottom line, I'm afraid the evidence in the GPX does not implicate the compass in any way. Don't you hate it when computer evidence flips the bird at your theory? :)

    Andy.
     
  3. Dave King

    Dave King Well-Known Member

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    Andy:

    I guess I am completely lost and dumbfounded. From everything I have seen, read on this board, or experienced personally an incorrect compass calibration can lead to flaky GPS performance and can cause issues when you are in AH and PH.Also when I had the signal of GPS lost, my data showed that I had 7 satellites and my AH and PH response was not very good. After I recalibrated the compass I had 60 minutes of perfect flying. IF you are saying this is incorrect and what I see is a coincidence I would trust what you say as you have the experience in this area more than I do.
     
  4. Gary Haynes

    Gary Haynes Administrator
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    Dave he wasn't using GPS modes or PH. It was all manual flight with AH being the only thing turned on.
     
  5. Dave King

    Dave King Well-Known Member

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    So I am clear for my own information. Your saying that Altitude hold isn't a part of the GPS or navigation boards? Can you perform AH without these boards?
     
  6. Gary Haynes

    Gary Haynes Administrator
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    Dave the AH sensor is on the FC board.
     
  7. Dave King

    Dave King Well-Known Member

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    OK, thanks for the info. I was completely thinking AH was part of GPS.
     
  8. Steve Maller

    Steve Maller UAV Grief Counselor

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    That is news to me, too. Interesting. Thank you, Gary!
     
  9. Gary Haynes

    Gary Haynes Administrator
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    The sensor is the one that is covered with Foam or some other material. On the bottom side of the board.
     
  10. Cedar Beauregard

    Cedar Beauregard New Member

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    I also think the extreme angle coupled with the helicopter trying its best to gain altitude brought her in... ​

    I had a very similar situation back in the single rotor days.. It was way out so I pulled back but because it didn't look like it was coming back I pulled back some more.. Well next thing I knew I was looking at the top of the rotor and it was dropping out of the sky :(.. It then rotated itself around because the tail couldn't hold and now was nosing into the ground top facing me at high speed.. Somehow I pulled up and it flew over my head at way over 80mph:) Was shaken for a while on that one.... And ever since I'm reluctant to pull back to hard knowing its probably coming even though I can't see it.. ​
     
  11. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Dave: The compass, GPS, and air pressure sensor are independent systems.

    The firmware on the FC/NC board combines the data it gets to do certain things: for example PH uses compass heading to control the yaw (I'm going from memory of the last time I looked at the code).

    The Navi board assumes that the compass data is accurate -- if it's not, then PH will be less accurate -- and you may see drift or flying in a small circle (aka "toilet bowling.")

    But the GPS data exists independently of the compass data -- the sensors do not interact.

    The issue is this: When you see "seven satellites" that means that GPS board has identified the radio signals from seven satellites. It does not necessarily mean that the signal it is getting is strong enough to be used as part of the positional fix.

    So, in that sense, you need to separate out "number of satellites" from "quality of data received from satellites."
    You can have seven satellites identified, but not yet have a valid 3D positional fix. The GPS Lost means, "ooops, I had a 3D Fix, but now I don't." It doesn't mean, "I had seven satellites, but now I've lost one/all."

    So -- separate number of satellites from quality of information received from them.

    AH does not require the use of GPS. I've flown on AH without the GPS having acquired any satellites. (I didn't mean to, but I have the Smart On Screen Display data recorded and the GPX file also confirms this). The AH worked fine.

    PH, of course, would be unusable as, absent any 2D or 3D Fix, it cannot be done.

    Hope that helps.
    Andy.
     
  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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  13. Joe Azzarelli

    Joe Azzarelli Active Member

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    David - my condolences. Anyone who has experienced this sort of thing knows the deep-in-the-gut pain and self anger that follows.
    There are 452 things to know and get right every time for a successful flight. I (we?) appreciate your willingness to share in order for others to learn and hopefully not repeat.

    This past week I had an incident that fortunately ended well but I would like to remind everyone to check the tightness of the blade nut on each motor before flight. I looked up and happened to see one blade "windmilling". The copter was sluggish and took a lot of power to arrest the descent but landing was soft. That did not make me feel any less stupid, just lucky.

    Joe
     
  14. David N Atkisson

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    Thanks for the input,

    A few notes. I always hot glue all my molex connections so nothing can vibrate loose. I also did have the compass calibrated and got all the correct tones as to it's calibration condition. Before I fly I always do an inspection of all nuts bolts and connections and check the Gimbal for CG. I have placed marks on all the various connections so I can tell visually if anything has slipped due to hard landings etc.

    The most obvious mistake in my opinion after looking at the data and listening to colleagues is the fact that I broke my own rule which is to fly my craft to far away so I didn't have enough visual cues to tell me if I was in control of it or not. Regardless of the mechanics of the crash I should always be able to see what I am flying and how my input is affecting the craft. According to the data, I was flying the copter over a quarter of a mile away from me and that is just to far to react responsively. In fact I had no idea I was coming back so fast because when the craft is coming at you there are no visual cues to let you know. I am usually a pretty conservative pilot but without knowing I must have had my stick pulled to far and brought her back to fast. The wind was slight yesterday but I could see it gusting at the upper levels via looking at the palm tree fronds blowing about. That could have contributed as well. I thought since it was so far away and the fact that I was going to fly straight out and back that putting it in AH was a good idea, but I failed to realize the impact on the craft if I flew to fast.

    I have learned a valuable lessen. It's hard to say no to the producer on a project but I guess I just need to stick to my guns and say no and mean it. It is a very hard thing to do though when it could mean severing ties with a client if they get to pushy. I just might have to grow a little thicker skin though. This was a very expensive lesson to be sure.
     
  15. David N Atkisson

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    One other thing of note.

    This might not apply to this crash but I recently have begun to have issues flying both Gruapner mx 12 for my Camera gimbal and mx 20 for my CS8. I did some on the ground range tests and noticed a beeping in my ear from the mx20 and everytime it beeped the telemetry side of the strength meter on my mx 20 tx blinked. I call Quadrocopter about the issue and they recommended that I rebind both transmitters again. Again I did the test with walking away from my copter and this time it happened and I noticed along with telemetry dropout I also was receiving data dropout from the strength meter on the left side of the mx 20 screen. I then called Quadrocopter again and they suggested that it might be a location issue of the two receivers. I use Quadropcopters Rabbit Ears setup on top of the copter for the the mx 20's receiver which is the one that I use to pilot the craft and I moved my receiver for the mx 12 down low and pointed it straight down for the camera gimbal control. this seemed to take care of the issue when I tested again.

    The main reason I was coming back home yesterday is because I heard the familiar drop out tone over my headset and that is why I immediately reversed and started coming back. Then of course the rest of the story is as we shall say now history.
     
  16. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    David:
    As you say, human senses are just not up to the task of measuring the heights, distances, and speeds at which we operate our copters.

    I certainly don't trust my senses -- for that reason I like to have (a) "Jeff's girlfriend" (the MK/Graupner telemetry) speaking me the LiPo voltage (so I don't have to look down), and (b) use a Smart On Screen Display so I can see the ground speed, nick, roll, current etc. while looking at the FPV footage.

    I cannot obviously rely on the OSD (or the day I do, it will fail), so one alternative strategy is to use Come Home when I feel the first tinge of anxiety (I test it each day on the first flight of the day). But each time I turn it on, I'm ready for it to do something silly, so I also practice the technique of rocking the C8 in roll so I can visually determine the roll axis, then rocking it in nick, and then my brain can lock on to the boom #1 direction and I can fly the C8 home manually. This is something I've practiced a lot on AeroSimRC (at Casey's suggestion) until has become fairly automatic.

    It's worth noting that the C8 will not drop out of the sky if you drop the LiPo below 14 volts -- sure you will need more throttle to keep it airborne -- and the LiPo voltage does decline rapidly, but, based on what I have read, there is the suggestion that you can sacrifice the battery and keep airborne until you get below 13.0 volts (you will lose FPV because the 12v RECOM shuts down).

    Also as you say, it is a valuable (and, sadly, expensive) lesson. Thanks again for your candor in sharing it with us all.

    Andy.
     
  17. Shaun Stanton

    Shaun Stanton Active Member

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    Another good technique that I use when I am flying beyond what I feel are comfortable limits is a safety spotter on a cell phone or two way radio at the end point of the flight path. I brief that person to alert me of any anomalies such as if LED's start blinking or anything else unusual. They can be good backup in this because the spotter could have alerted you that the A/C was coming back to you as well.

    One of the things I practice on the sim in addition to what Andy mentioned, is that I practice distance flying. If you are holding a level altitude the A/C should appear to be climbing as it is coming back towards your direction.

    Your spotter should see it appear to be descending as flies away from him. If both of you see it descending then it is descending. If the spotter sees it staying at a level altitude or climbing and you see it also climbing than it probably is in a climb. I use crew coordination to alert the spotter on what I am doing so they are alarmed if they see the A/C climb or descend.

    As for the FPV, I use a separate 12V battery a small 1100 3S Hyperion or Turnigy battery to power the camera and video down-link so I do not get a video blackout in the situation that Andy mentioned. The onlything on my FPV that is drawing power from the main board is my small 5g micro servo that I have tied into the FC for my small Nose cam gimbal tilt control and compensation.
     
  18. Jonathan Keao

    Jonathan Keao Member

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    Here's my newbie take on what I've read...

    The recipe for this terrible mishap appears like it can be prevented with software (or settings) changes. Software logic that protect us from lapses in human judgement exist in all sorts of systems. I'm sure there are some on the MK boards already, but I just don't know enough to name one. I mean, there conceivably has to be an on-board algorithm that would prevent the 'perfect storm' of inter-related manual (excessive nick) and automatic (AH) control signals from sending potentially disastrous orders each and every time.

    There seems to be enough mechanical and electronic triggers that one (MK, in this case) could use to determine whether we're asking our copters to do too much at once.


    Finally... WOW! I read and re-read this whole thread a few times. I'm sure there are other threads that are just as informative for a newbie like me. If there isn't a thread that houses links to star quality threads, there ought to be one. The incident is definitely unfortunate, and I feel bad for David. I also can't imagine how my first crash will be, but I know I'm better prepared and more informed because of the brilliance exhibited on this forum.
     
  19. Shaun Stanton

    Shaun Stanton Active Member

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    Not really. There sort of is. The default setting 3 called Easy mode prevents the copter from going past 45 degrees of pitch and roll in Freefly mode. It does not work in conjunction with altitude hold. 40 degrees in his case is enough to force the copter down while it was providing max throttle gas. He had the Aircraft travelling a mzx speed of 55.8 MPH. AH is only controlling throttle gas to try to keep the baro altitude stable, but once you go over limits such as weight to thrust available it will not over ride your inputs. In an ideal situation AH would override your pitch/roll commands and limit your ability to over control the aircraft but it doesn't. The only way you might have this control is if you had Dynamic Position Hold assuming good GPS signal enabled then the copter will travel to a point that you are commanding to internally at a predefined rate in copter tools.
     
  20. Steve Maller

    Steve Maller UAV Grief Counselor

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    I doubt there's a one of us who hasn't "crashed" (that's a pretty broad description...some might consider most of my landings "crashes"). But with each mishap of your own or others, you should grow more informed, more careful, and more aware. This forum is super useful, and each of us feels a communal responsibility to cast aside our egos and share our experiences.
    Welcome to the forum!

    PS: my worst crash with my Cinestar is documented here: http://forum.freeflysystems.com/index.php?threads/today-carefree-mode-bit-me-in-the-ass.538/
     
    Shaun Stanton likes this.

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