ALTA death spiral and crash

Discussion in 'ALTA' started by Adam Varadi, Nov 26, 2015.

  1. Steve Maller

    Steve Maller UAV Grief Counselor

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    Paraphrasing what the main character said in "The Martian", it's amazing what you can find when you "...science the sh#t out of this". Thanks for taking considerable time and resources to suss this out, Andy. You're an amazing asset to this community!
     
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  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Thanks, Steve. Just wish there was something more dispositive in the data.

    Andy
     
  3. Stefan Helborg

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    You wrote that "ALTA app says Motor FAIL". Which motor is it, and you can see any damage on the specific motor. For example, loose wires, loose head, bell, etc.?
     
  4. Mateusz Hajdziony

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    Good job Andy!

    @Adam - did you check Sun's activity the day you were flying?

    I have taken a look at the recovered log that Andy has posted, and from the log I can read the course of action like that:

    1. You were in GPS position hold, you were descending at around 2m/s (throttle stick at around 25%), while going forward very slowly and yawing left slowly. There was probably a bit windy because, although your roll stick was in the middle, there are some fluctuations in the roll data, so it means some oscillation, probably caused by wind (or maybe a descent in prop wash)
    2. Radio signal is lost - Synapse commands altitude and position hold
    3. Given that you were descending, Synapse tries to hold altitude and commands the motors to speed up
    4. The motors do speed up - accelerometer reads vertical acceleration up at around 3m/s2 (and that would mean that the ALTA is slowing down the descent to hold altitude), vertical velocity is going down (ALTA braking the descent) BUT
    5. Data from ESCs hangs at constant RPM, until the end of the recovered data. RPM is constant, voltage and current are constant, from every ESC.

    So, this shouldn't be the case because the FC is constantly changing something. Fine tuning motor RPM - the voltage and current should fluctuate. This all starts during radio LOS event, but two log ticks before first I2C error. Worth noting is that the motor RPM values froze at values that were the same as during the descent. That tells us that the FC commanded motors to speed up (to keep the altitude) and they responded with RPM change, at least at first (because the craft slowed its descent as shown in ACC and baro data), but the data from ESCs never made it to the FC, that's why the FC has logged the last known motor data.

    Unfortunately the log ends after few clock ticks because most probably, as Andy said, the failure caused a chain reaction. Looks like MAG has failed first, then radio signal, then data from ESCs and then I2C bus. The log ends so the FC has probably failed shortly after. It's a pity because we could be able to read what the FC though it was doing.

    To me it looks like the electronics have failed badly. I'm surprised a bit that Freefly is still using I2C bus for communication between components - I was under the impression that the industry has agreed that I2C is bad for long distance communication (e.g. bad for communicating between, for example, FC and ESCs). I2C is fine to send data between components on a single PCB, but really prone to interference over long distances. The longer the distance - the easier it is to disrupt the data flow. Especially since the ESCs are placed at the very end of arms in ALTA. They should have used CAN bus - much more resilient when it comes to interference.
     
  5. Mateusz Hajdziony

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    By the way - the log says that you were 14 meters above ground when all this happened, so it definitely means that we are on the right track.
     
  6. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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  7. Adam Varadi

    Adam Varadi Member

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    Andy,

    Thank you very-very much for your help and dedication to this matter! I would be happy to send some hungarian salami to you! :)
     
  8. Adam Varadi

    Adam Varadi Member

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    When I boot it up all the boom LEDs are blue indication esc or motor problem. None of the motors spool up even when I try to do so from the app. No phisical damage from the outside, but I don't want to dissaseble them before freefly sais something. (By the way they still haven't responded)
     
  9. Adam Varadi

    Adam Varadi Member

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    It's weard to see that you could reconstruct my flight just from these files. :)
    But you are absolutly right, there was wind.
    The radio failed too since I didn't have any control even after crash while I tried to stop the motors.
     
  10. Jan Evers

    Jan Evers New Member

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    Hey Adam,
    I wonder a bit, as the log says that it detects a Radio LOS, this should normally not work when using a Graupner with PPM, right?
     
  11. Adam Varadi

    Adam Varadi Member

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    You are right!
    This is why the normal go home doesn't work.
     
  12. Steve Maller

    Steve Maller UAV Grief Counselor

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    If my memory serves, Freefly are using both CANBUS and I2C in the ALTA, and one will fail over to the other in the event of a problem. I'm not sure which one is the master and which is the secondary, although I think it's CANBUS that's primary. But one of the Freeflyers is going to have to take it from here. I know there's little/no transparency into the inner workings of the SYNAPSE, but I do know that they said there is redundancy on the bus.
     
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  13. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    The bad news is that the U.S. Agricultural Department would confiscate it because they have not inspected it!
    The good news is that there are places in the USA that do sell PICK that has been "blessed" by the US Ag. Dept. :)

    It's my colleague, Robert Young who deserves most of the thanks -- he did the forensic recovery and searching for the missing data rows. He found them in unallocated space on the microSD card -- they have been written to the card but not yet made part of the actual log file. This is what happens when you write data to the card but the process is not allowed to complete normally.

    Andy
     
  14. Adam Varadi

    Adam Varadi Member

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    Please give him my thanks!

    I'm kind of sad, FF still haven't responded and the worst part that I have a 4 day long shoot, and already lost 1 day because of this. The guys at kopteworx are really nice, they told me that they can give me an alta if FF says it's ok, but still waiting for them...
     
  15. Adam Varadi

    Adam Varadi Member

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    Finally FF responded. They want me to send out the copter, can't do anything else. This would be ok if they would aggree to lend me one as replacement. I'm seriusly thinking of sending this back and buying an X8...
    (And still think this copter fly the best!)
     
  16. Adam Varadi

    Adam Varadi Member

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    Final words from FF, only repair. It would take 10-14 days at least in total. :-(
     
  17. MIke Magee

    MIke Magee Active Member

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    Adam, ALL of us are watching this issue.

    On the one hand, Freefly needs to manage customer issues in a professional and even handed way (their entire SB process is a great example of the best support I've seen for UAS's).

    On the other hand, your customer loyalty and investment ("ALTA, Cinestar, Movi M15, Movi M10, Movi M5") along with the fact that it's crystal clear you didn't fly into the side of a building - that given the logs, there may have been systemic failure, give me pause.

    I would hope that Freefly reconsider their approach, and to support you more aggressively.

    It is clear to me that EVERY existing and prospective Alta owner is watching this issue very closely.

    Best of luck.

    -m

     
  18. Michael McVay

    Michael McVay Active Member

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    Agreed - and well stated.
     
  19. Mateusz Hajdziony

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    Well said Mike! I think that Freefly should absorb the loss, give Adam a new ALTA (it looks like Kopterworx thinks the same) and get the old one to US for testing to see if the crash was caused by something that all ALTAs could suffer from in the future. The ALTA may retail for $8k, but it's not like producing one unit is close to that amount of money.
     
  20. Adam Varadi

    Adam Varadi Member

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    Hy guys,

    Thanks for your support.
    I liked FF since they were alwayse helpful and quick when I had issues with the Movis, not sure why it's different with the ALTA.
    Very dissapointed in FF!
    By the way, first they wanted me to send the ALTA to them and the I can get store credit for the shipping cost. After some mail I was able to make them do all the shipping, I just have to give it to FedEx.

    After all I'm in talk with the guys at kopterworx and seriously thinking about buying a Hammer X8 instead of the ALTA, so When I get it back, might have one for sale...
     

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