Crash on maiden flight- need help

Well, I should have taken the advice of, pretty much everybody, and built a simpler model as my first build. But I didn't... I jumped right in and built a DYS D800 X8, and a Tarot X6 at the same time. I took the D800 X8 out yesterday for her maiden flight.

I really took my time building this thing. I studied everything I could find. I used a Pixhawk, and I very carefully did all of the calibrations, and motor checks in Mission Planner. From my limited experience, it all looked good. Motor numbers, and rotations all look good. I was very careful about installing the props. I'm pretty sure I got all that right.

Here's what happened: I found a great place to maiden flight. Set up everything. radio on. Battery on craft connected. Tower as a GCS. Everything looks good. Good GPS. I armed the craft, and got very nervous, so I disarmed. Did that about 7 times. Finally got up the nerve to go for it. Throttled up, and she rose a bit and immediately did a very fast back filp to the port side and landed about 10 feet away. Some damage, but it can be repaired.

Now I'm trying to figure out what went wrong. I'm a beginner at all this, and reading flight logs. At first glance it looks as though the voltage drops out, and the current spikes as soon as I throttle up. After adding a few more lines to the chart, it looks as though the barometer is going crazy each time I armed/disarmed (when the props spin). The barometer really went crazy on the fateful throttle up.

Could one of you kind folks please take a look at my flight log to help me determine what went wrong and how to fix it? I'm a beginner who took on way too much. However, I am a quick learner. I just need some help. I have attached the log. Any help would be greatly appreciated!

2017-01-18 12-28-14.log

2017-01-18 12-28-14.bin

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  • It's a bit difficult to know what the problem is from your description  (and I'm not familiar with DJI flight controllers).

    By payload do you mean AUW (all-up weight)?

    Let us know more details of your build (motors, props etc ) and we should be able to figure out if that battery can provide enough current.

    Justin


    Peter Farnsworth said:

    Perhaps I should have posted this in a new thread...Related question about the Multistar 14.8 volt 10000 10c batteries which I am also using on my x8: With a 10 pound payload, and with motors and props that calculate the max lift should be 21 pounds, I get the red-blinky warning light about 30' seconds after liftoff. This is using the DJI flight controller. Happens regardless of which of the 2 batteries I use.

    I don't know how to measure the discharge rate, but I am supposing I need a 20c discharge rate instead of the 10c one. (I will read other posts to try to figure out how to hook up a measuring device.)

    Any thoughts are appreciated.
  • Perhaps I should have posted this in a new thread...Related question about the Multistar 14.8 volt 10000 10c batteries which I am also using on my x8: With a 10 pound payload, and with motors and props that calculate the max lift should be 21 pounds, I get the red-blinky warning light about 30' seconds after liftoff. This is using the DJI flight controller. Happens regardless of which of the 2 batteries I use.

    I don't know how to measure the discharge rate, but I am supposing I need a 20c discharge rate instead of the 10c one. (I will read other posts to try to figure out how to hook up a measuring device.)

    Any thoughts are appreciated.
  • Thanks Justin.

  • Easily overlooked, but possibly one of the most critical components in your rig!

    I'd suggest next time you test, set the failsafe to Land rather than RTL. 

    Once you're happy with how it's flying and have tested GPS modes (e.g. loiter) are working correctly, then you can enable RTL failsafe again.

    Let me know how you get on!

    Justin

  • Ordered. Thanks for the suggestions. Seems like a no brainer that I didn't even think of.

  • I'm actually in the UK and ordered from AltiGator but the 2 LiPo kit from Craft and Theory looks like everything you'll need.

  • OK, good to hear you are using the Multistar 10C batteries.

    I'll order the suggested parts tonight. Did you order from Mauch, or one of the US resellers? Craft and Theory has a Pixhawk/2 lipo kit.

    Thanks!

  • I had a few kind people help me out when I first got started so feel obliged to give something back!

    I'm using the the 12000mAh version of the Multistar - the 10,000mAh is totally fine though, although I'd suggest running two inparallell as you won't get great flight times with only one.

    I think we need to focus purely on the power system. Your log shows that with all 8 motors at full throttle, you're only pulling 56 amps so your current sensor has not been calibrated properly.

    Are you using the standard 90A sensor that comes with the Pixhawk?

    If so, you need to replace it STRAIGHT AWAY (don't fly it!) as it's really not designed for big rigs like this and they can burn out cutting all power to the copter

    I'm using a Mauch current sensor (http://ardupilot.org/copter/docs/common-mauch-power-modules.html) and would suggest you buy his 200A sensor and his 5.35V 2-6s BEC as a minimum. They're great and the developer (Christian Mauch) responds to e-mails and even gives you calibration values you can just type into mission planner so you know you'll be getting really accurate readings.

    I've done this slightly differently and used 2 x 100A sensors, the "Sensor Hub X2" and 4-14S Hybrid BEC as I am using two batteries in parallel.... if you can spend the money (and you really shoudl!) this is a very worthwhile upgrade.

    You'll need to be handy at soldering though as you'll need to wire these directly to the main PDB and make a really strong connection to handle the current.

    MAUCH Power Modules — Copter documentation
  • Thanks for taking a look Justin. I really appreciate it. Always amazing when total strangers are willing to help out. I suck at building and flying, but at least I have interacted with some really cool people.

    I'm using this battery: https://hobbyking.com/en_us/multistar-high-capacity-6s-10000mah-mul...

    What battery are you using? I'll order them tonight.

    Thanks!

    Multistar High Capacity 10000mAh 6S 10C Multi-Rotor Lipo Pack XT90
    Multistar High Capacity batteries are the result of extensive testing with one goal in mind. Increasing flight times for multi-rotor without the pena…
  • Yes, the battery failsafe triggered and then it switched to RTL and so actually tried to gain altitude to fly to the home location. 

    It looks like your motors are wired up OK now though which is a good start.

    Your battery voltage does sag a LOT as you say. What are you using? Also, what are you using for the current / voltage sensor?

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