Bad crash with Cinestar/Mikrokopter and Graupner MX20 combo

Discussion in 'Cinestar 8' started by Tim Sessler, Sep 28, 2014.

  1. Tim Sessler

    Tim Sessler Active Member

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    Hi guys -

    Earlier this week I had a pretty bad crash with my X8 that pretty much just fell out of the sky from about 100ft. In the aftermath I figured out a lot of things that I just wanted to share with everybody to hopefully prevent similar accidents in the future.

    Here is the rig that I was flying: Cinestar X8, MK FC 2.5 with MK GPS, Castle 50A ESCs and i2C converter. KDE 4014 motors with Tmotor 17" props and dual Freefly 6S 9,000mAh lipos. MoVI M10 with a Canon 5d. Transmitter was a Graupner MX20.

    The incident: We were flying for about 1.5 minutes, hovering above a tree at around 60ft high, as my Graupner MX20 suddenly started beeping, signaling that it didn't have any connection to the Rx anymore. Of course any of my stick inputs stayed without any result and after a bit, the Cinestar started slowly drifting back towards the point where we took off from. Once I realized that it wouldn't just land in front us but keep moving towards (and above) more big trees, I got fairly concerned. In a last resort effort I turned off the transmitter and turned it back on, hoping that for some miraculous reason it would reconnect. Nearly the same moment the Cinestar suddenly just fell out of the sky. Crashed into the tree, took a massive branch down and then slammed onto the ground.

    The result: all 4 booms broken, all 8 props broken, Canon 5d broken in half, lens snapped off, MoVI M10 broken in way too many pieces. And if that wasn't enough, one of the 6S lipos caught on fire a few minutes after the crash. Luckily I had put it in a lipo bag by then, which contained some of the fire. Though it still filled the whole park with smoke and even dunking it in a puddle didn't help as its a chemical fire (the Fire-department showed up 10 minutes later but at that point it was all burned up and they couldnt care less - but thats a whole different story).

    The cause: thats the main reason why I wanted to share this incident and hope that it makes other MK rigs safer in the future.
    1) After a range check a few days later, I found out that the antenna of my Graupner MX20 was internally broken. If pointed forward the transmission strength and quality drops incredibly fast to the point that the connection gets lost all together. If the antenna is pointed straight up though the contacts inside somehow connect again and the Rx quality goes back up to the high 90%-values.
    Lesson number 1: make sure that your antenna isn't damaged and lesson number 2: do a range check before every shoot.
    2) The reason why the copter just fell out of the sky vs. having a nice, slow and elegant emergency landing was one very simple reason. Even though I knew about that, for some reason in my MK-tool MISC settings the "Use Vario Control For Failsafe Altitude" was unchecked. Which means instead of landing at 95% of the hover throttle the copter was now descenting at a 95 throttle stick value - my hover throttle is around 70%, which would be equivalent to a 180 throttle stick value. 95 of course won't get you very far, if you're looking for a smooth landing.
    Lesson number 3: make sure you have "Use Vario Control For Failsafe Altitude" checked in your MK settings. Also make sure your "not start without GPS fix" is checked.

    Vario Control failsafe.png

    MK Tool MISC marked.jpg


    3) And last but not least: this unfortunately is something that you could only control to a certain extend: In my case, even if all the MK settings would have been correct and it would have executed a perfect emergency landing, there is one issue that would have still been fatal: the MK didn't exactly start the emergency descent above the come-home-possition (the point where it took off from) but moved about 50ft past that spot and therefor would have descended nicely into the tree. The total damage might have been less - but still its not the ideal scenario.
    I shared all this information with Holger from Mikrokopter and he is aware of this "bug" and will fix it in the next firmware update.

    Until then - be careful out there and please do yourself the favor to just quickly double check that those two boxes are checked.

    Cheers!
    Tim



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  2. Jason Smoker

    Jason Smoker Active Member

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    Wow! sorry for loss! that looks bad :(
     
  3. Michael McVay

    Michael McVay Active Member

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    I'm really sorry to hear about all the equipment that you lost in the accident. I'm glad nobody was hurt at all.

    Thank you very much for sharing the experience with all of us - and hopefully preventing someone else's similar accident.
     
  4. Gary McCready

    Gary McCready Active Member

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    Tim: so sorry, man. Thanks for posting and letting us know what the problems were.
     
  5. Steve Maller

    Steve Maller UAV Grief Counselor

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    Holy crap, what a mess. Much to learn...thanks for sharing.
     
  6. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Thanks for the publishing this Tim. Sorry to see this happen, but glad I was able to help by analyzing the GPX file and the MK Tool settings for you -- where's the UAV Grief Counselor when you need him, eh? Probably on vacation <wink, wink, nudge, nudge...>

    The specific settings are in the MISC tab of MK Tools -- it's a setting that I think MK should issue an on-screen warning about....I cannot imagine the circumstances where, on loss of Tx (aka "Sender") signal you would ever want to put in an absolute number for Emergency Gass setting so low that it would ensure a crash. The documentation warns of the problem -- but why not have the software tell you, eh?

    The correct position for an an antenna to get the maximum amount of RF power up in the sky is vertical, or even leaning backwards away from the copter slightly. Extend a line 90 degrees out from the long axis of the whip antenna in all directions -- that's the maximum signal direction.

    The lose antenna connection really does demand a Range Check every day before one flies, but it's easy to skip that stage in the interests of getting airborne. AMHIK. :rolleyes:

    Andy.
     
  7. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Oh..the UAV Grief Counselor lives. I'll eat my words!
    Andy.
     
  8. Steve Maller

    Steve Maller UAV Grief Counselor

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    Actually, in my experience, I have seen slightly better results with the antenna bent at 90° and rotated 90° to the left or right. This way it has decent polarization when it's directly overhead, as well as at a distance. The only place it won't have great coverage is when the antenna is pointing directly at the copter, but in my case, I'm generally facing the copter, so this is not an issue.
     
  9. Tyler Olson

    Tyler Olson Member

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    thanks for the warnings and story. perhaps a very good argument to carry a fire extinguisher in the car as well.
     
  10. Holger Göhr

    Holger Göhr New Member

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    Sorry for your crash.
    It also pays to check fail safe.
    You can actually put it on a switch and simulate switching the remote off, without switching it off.
    That way you can interfere quickly if fail safe is not doing what it is expected.
    I personally don't like to really switch my remote off, so this is a great way to test the function.
    I noticed the last time while it climbs in RTH to my assigned altitude of 30m, in Radio fail safe it came home in a direct line without climbing to altitude first..
     
  11. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    That works if, and only if, you're facing the copter (that is, the antenna at 90 to the copter). If the copter's off to one side or another, then the RF side-lobe (to give it its high fallutin' name) will not be "pointed" at the copter. Any EE out there with a background in RF antenna theory? Please correct me if I'm wrong. :)

    Andy.
     
  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    The conventional wisdom is that LiPo fires, because Lithium burns to well, require a Class D fire extinguisher. Typical costs for such an extinguisher are $400.

    It's not clear when you read documents like this: http://amerex-fire.com/wp-content/uploads/2013/03/Extinguisher-Myth-32.pdf
    whether a Class D really is required or it's just a vicious rumor started by the Class D Fire Extinguisher Association of America to drum up business. :rolleyes:

    Andy.
     
  13. Ozkan Erden

    Ozkan Erden Distributor

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    I'm sorry to see this. And thanks for sharing your findings.
     
  14. Steve Maller

    Steve Maller UAV Grief Counselor

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    I've seen evidence that the best way to extinguish a LiPo fire is a bucket of sand. But that's not so practical, is it.
     
  15. Gary McCready

    Gary McCready Active Member

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    Re Lipo fires:
    My son, the Fire Protection Engineer, say ABC is fine for Lipo's. He also said it is best just to let it burn, if possible, not get close, because they can explode. D is for burning metal fires, sometimes specific for the metal type, not just the extreme heat.
    He said you can look it up in NFPA 10, what ever that is.
    (FYI: he is an "engineer", with Univ of MD degree, I know I paid for it..lol)
     
  16. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Thanks for the info, Gary -- and for paying for your son's education! :)

    Andy.
     
  17. Dave King

    Dave King Well-Known Member

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    HI Tim

    Thanks for sharing and being brave enough to post. This looks like one of my wrecks :eek:

    My best to a speedy recovery and rebuild.

    A few things that I wanted to share with you that stand out to me after reading your very well detailed report.
    1. I always set my CH altitude to 50 meters so that it clears all tall trees even though I know that this is not what happened to you it sounds like it could have but missed them.

    2. You can set the time before it goes int emergeny landing after it comes back home. This could give you some extra time if needed. I used to have an extra radio ready to go in case something like this happens but I found that the receiver can be bound to only one
    TX at a time so you wouldn't have been able to whip out a spare radio and turn it on to save it. I set my emergency gas time pretty high around 250.

    3. I don't believe that if you set your Emergency gas to 90% its 90% of your hover gas in vario mode. From what I understood its 90% of your throttle. If I'm wrong someone please slap with me with a big trout. From the experiments I performed with a mid payload the copter kept dropping very fast not matter the number I used. I did a few emergency gas tests and found the need to abort it once it go to about 40 feet away as it was dropping way too fast at that point. Haven't had a chance to revisit this to see what the actual problem was or what it needed to be set to. I had verio checked. When I did the tests I did it with my older 4S system and QC 3328 motors that had about a 65% hover throttle with the Sony 760 camera back then.

    4. Your hover throttle with the 4014's at that payload seems like the I2C converter is very inefficient. With the MK electronics, MK power board, 4014's X8, and a red scarlet (25 pounds all up weight) I was about 64-65% hover throttle and 58-60% throttle with my 5D payload.

    5. Test your motors really good if you plan on reusing them. I found a crash that hard really changes the tolerenace is the bearings a lot. I would also upgrade your motors shafts if you haven't already done so. A few guys snapped the snaps with a similar to yours.
     
  18. Derek Cooper

    Derek Cooper Active Member

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    Reminds me to re-check my TX failure setup..
     
  19. Tim Sessler

    Tim Sessler Active Member

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    Thanks for the kind responses everybody!

    It looks like I'll be able to re-build everything by tomorrow, just within 7 days. Not too bad. KDE helped big time with replacing shafts, stripped power cables and bearings within a day and overnighting everything again, well thats customer service!!

    3.) That would be interesting to find out. 90% of my throttle wouldn't be the best settings haha
    @Andy: do you know more about this?

    4.) The AUW weight was probably comparable to a light Scarlet/Epic package, as I have the 5D on a massive base/cheeseplate, with added Glidecam weights and a 4S 5000mAh lipo that powers the camera. Probably 25-27lbs. Not the lightest flight set-up but the best result with the MoVI M10.
    Yet I agree: my hover throttle always seems awfully high. I am just building a Gryphon with KDE 5215-435, 18" props and Herkules III setup - if it works well, I might switch over my Cinestar with the 4014s from Castle ESCs and i2C converter to the Herk. Would be interesting to see a direct comparison.

    Cheers!
     
  20. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Afraid not. If I understand what Dave wrote he's saying that there's a major bug in the MK Firmware in that it doesn't apparently do what it is supposed to when the Vario checkbox is checked and the Emergency Gas is set to, say, 95%. The documentation says that it's supposed to be 95% of the automatically determined throttle needed to hover -- and that should produce a descent that will not result in a crater on landing/impact.

    Am I understanding you correctly, Dave?

    Andy.
     

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