Crash after 40s - GPX file attached... What on Earth?

Discussion in 'Cinestar 8' started by Ben Freedman, May 10, 2013.

  1. Ben Freedman

    Ben Freedman Member

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    Howdy...

    So, after several successful flights yesterday, today I had a disaster...

    Took off under calm conditions. Hovered for 20-30s in a stable flight. Began a slow climb, and the heli just dropped out of the sky, pretty much straight down. It looked like it was a 100% sudden loss of power.

    I haven't examined the heli yet, as I'm writing this from a nearby Starbucks where I'm drowning my sorrows.

    Can you take a gander and this GPX file? I can't find anything out of the ordinary. The motors are drawing very different amperages, but that's ALWAYS been the case since I built his heli... so while that may be strange, its' not out of the ordinary for this bird...

    Thanks for any insight you may be able to offer. I'll update after I examine the heli back at my studio.

    Best,

    Ben

    Benjamin Freedman
    PrimeImage Media
    480-399-0000 - direct
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  2. Gary Haynes

    Gary Haynes Administrator
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    Ben just looked at your log. Looks normal but only runs for 40 seconds. Low number of satellites at average of 5 but you didn't engage PH until the last three seconds.

    Andy may know what happens to the log file with a sudden power loss. I would suspect that a battery/power cable came loose. Take lots of photos.

    Sorry to hear of this.
     
  3. Shaun Stanton

    Shaun Stanton Active Member

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    I do see something wrong. Something weird with your Baro. Your aircraft was constantly showing a descent even when your baro shows you climbing when in fact you were descending the entire time. If you look at your vertical speed you can see that it is always negative even though the aircraft's altimeter thinks it is climbing. If you look at GPS Elevation it is descending. So what happens is that the copter is trying to descend to correct for altitude but is thinking it is climbing so it is trying to correct for the altitude that you engaged AH at and descends into the ground.
     
  4. Ben Freedman

    Ben Freedman Member

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    That is odd. Will look closer.

    However, I don't think that should explain the sudden loss of power...

    B.
     
  5. Shaun Stanton

    Shaun Stanton Active Member

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    Here are the last 14 seconds of the flight log.
    Altitude(ft) VerticalSpeed(ft/s) Elevation(ft) Variometer

    23.950059 - 4.1666668 26.24664 7
    28.215138, - 3.8713912 26.24664 16
    32.3161755, -5.7086616 22.96581 15
    31.3319265, -8.9566932 16.40415 -3
    30.0195945, -7.874016 16.40415 -4
    30.0195945, -7.1850396 9.84249 -1
    29.855553, -5.8398952 13.12332 0
    29.52747, -4.4619424 19.68498 -2
    29.199387, -4.6916012 16.40415 -2
    29.52747, -4.7244096 16.40415 0
    28.543221, -4.7244096 16.40415 -3
    27.887055, -5.085302 13.12332 -2
    28.215138, -5.8398952 9.84249 -2
    28.871304, -5.905512 3.28083 It thinks its at 28 feet when in fact it is impacting the ground!

    Notice that Vertical Speed is constantly showing a descent but the Variometer shows a climb on the magenta rows. Also notice your Baro altitude on the far left shows a the altitude around 30 feet. Also Notice the elevation from your GPS is showing what the copter is actually doing. Either something is terminally wrong with your Baro ie altitude sensor, or that there is something clogging it up. My guess is something is clogging your Baro under the FC board. Because the pressure does not seem to change and the copter pretty much thinks it is holding the commanded altitude, when in fact it is descending.
     
  6. Shaun Stanton

    Shaun Stanton Active Member

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    It very well could, George(a name we call autopilot's in the airforce) is sometimes a bumbling retard. If the copter thinks it is climbing and not doing what it is supposed to it will keep throttling down and down to try to achieve the commanded level.

    I had it happen to me in my Hex flying Arducopter APM 2.5. I had an incident in Arducopter where it thought was 400 feet higher due to an anomaly with its baro. It went straight to idle. Luckily it was at 250 feet enough time for me to catch it and go manual and throttle up. But absolutely the system is trying to compensate for what it is being commanded, if the information is wrong, it will just blindly fall out of the sky. Its GIGO, garbage in garbage out.

    Sorry it happened hopefully we can get to the bottom of why it did this. I am pretty confident that it was the Baro.
     
  7. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Sorry about coming to the discussion late. My windows machine is not available right now as it's being backed up.
    Shaun's analysis sounds valid, but, of course, is puzzling.
    Given that you switched to AH (based on what Shaun said), the behavior points to the pressure sensor fooling George (he's sometimes known as Otto, as in Otto Pilot ;))

    Did the FC board survive the crash in one piece? I'd like to see an image of the pressure sensor to see if all the legs and solder joints are intact?

    Andy.
     
  8. Ben Freedman

    Ben Freedman Member

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    1 hour after I post is not exactly late, Andy...

    I'll take some shots back at the studio shortly.

    B.
     
  9. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    It's a lifetime on the Internet (or so I'm told), Ben.
    OK. I'll stay hunched over my keyboard until then.... :)
    Actually, I'll be off line until later on today.

    Thanks
    Andy.
     
  10. Steve Maller

    Steve Maller UAV Grief Counselor

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    You were flying with Altitude Hold on, and at the last minute you also engaged Position Hold, and it looks like the copter was confused (as per Shaun's observations above) and it literally flew itself into the ground.

    I still don't understand the use of AH and PH for active flying. If you're trying to hover, that's one thing. But using it to fly around seems odd. If you can fly your copter, then fly it. If you can't, then maybe you should practice more. I use AH and PH to do just that: hold the copter.
     
  11. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    My hunch is that there was a component failure -- it's hard to construct a scenario where AH and PH would conspire to fly a copter into the ground without such a failure.

    To address your AH/PH question, Steve. I routinely get asked to make long low passes along roads, or following things -- I use AH to avoid to main more or less constant height -- it's one less dimension to fret about while trying to maintain a straight ground track or following something/one on the ground.

    Do I rely on AH? Nope. I really don't trust it, so I have to be vigilant that it's working correctly -- but by keeping one eye on the Smart On Screen display of the FPV view in the Cinemizers I can keep "polling" the altimeter.

    I will use PH if I'm shooting stills (just to minimize aircraft motion) or the camera op wants a "straight down" or high-angle shot -- it helps to avoid drifting laterally. I test PH and Come Home on the first flight of the day, though. Distrust but verify!

    But, as you say, I make a point of flying without AH and PH just to keep my hand/eye coordination ready for the day when the AH/PH/Smart OSD/FPV all collapse in a heap.

    Andy.
     
  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    By the way, I did look at the GPX file. I agree with Shaun's assessment. The GPS elevation shows reality. The pressure sensor's altitude shows bogus information -- which is why the AH failed to add throttle to prevent the descent.

    Andy.
     
  13. Shaun Stanton

    Shaun Stanton Active Member

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    Here is another on of my high quality drawing illustrations to demonstrate this. Not sure why the baro did this, but it looks like the classic case of what happens to an altimeter in an airplane if the static port gets clogged.
    baroerror.jpg
     
  14. Ben Freedman

    Ben Freedman Member

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    Yes, but it didn't really 'throttle back'. Rather, it lost power and fell from the sky.

    Upon examination of the board afterwards, it appears that my main battery power connector positive lead (where connected to the board) came unsoldered. Don't know how or why. Solder joint seemed VERY solid to me, but obviously wasn't.

    I guess there's a chance that it separated in the crash, and that it's not what caused the power loss... if so, then I'm still at a loss for why it died.

    So, my theory is that power lead came unattached, which I guess is ultimately pilot error, since I put it on there in the first place.

    Any idea as to when the FF power board and controller will ship, and how much it'll cost? I've pretty much had it with the MK stuff.

    Best,

    Ben
     
  15. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Ben: If you have time could you take an image of the PDB showing the point of separation and also the end of the battery power connector where it separated (specifically the surface that would have been attached to the PDB). We might be able to infer some information about what happened from those images.

    A
     
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  16. Steve Maller

    Steve Maller UAV Grief Counselor

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    That might also explain the loss of some of the data in the GPX file, because the main LiPo(s) also powers the FC & Navi boards.
     
  17. Gary Haynes

    Gary Haynes Administrator
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    Ben the Freefly Motor Control is available now. You would need to use something like the Abusemark I2C converter with an MK setup. QC has them.
     
  18. Shaun Stanton

    Shaun Stanton Active Member

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    Can you post a video as well to rule out the cable coming loose on the PDB in flight or ground? The motor sounds will give a good clue.

    Shaun
     
  19. Dave King

    Dave King Well-Known Member

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    Andy I also use PH when I am trying to fly down in a long straight line (400 meters) as it helps minimize drifting from side to side. I have been practicing doing fly overs for a golf course and found that at least in my circumstance, PH helps me fly in a long straight line more consistently. Now I do admit that I am not the most experienced pilot and maybe I do not have the best skills to fly straight without PH but I am always practicing without PH to improve those skills. What worries me about PH is that you are at the mercy of the GPS signal and that's just another thing to be concerned about when flying.
     
  20. Dave King

    Dave King Well-Known Member

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    Andy IF AH was off in this situation would the pilot have been able to correct to avoid the crash or would the failure of the pressure sensor mean doom in manual control?
     

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