Voltage drop

I'm having a real boring issue with the hexacopter starts beeping and warning for low voltage as soon as I take off.
It doesn't warn when I take off without the camera gimbal attached.

My spec is:
Pixhawk with 3DR power module
Tarot 680 Pro
6x Sunnysky V3508 700kV
13 inch props
DSLR Gimbal with SToRM32
2x Multistar 5200mAh 4S 10C

I'm having the two batteries wired in parallel and that should add up to 20C discharge rate=able to deliver 5.2*20=104Amps.

Surely, my hexacopter can't draw this much and cause the batteries to drop so much in voltage?? Please help!

The voltage

j1uhdNs.png?1

The current
2jTT4fX.png?1

2015-10-18 17-58-52.log

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      • well heres the thing 3lbs i mean come on.. that sucks battery power... big time... you have to balance everything just like in life balance your check book balance props balance weight to thrust   expecting a copter to lift all that weight then crying when you only get 2 mintes of flight when you normally get 20 come on lol

  • I have been looking at the Tarot 4114 320kv motors. Seems like alot of people get really good flight times with this and 15" props. Would you please confirm that these are efficient Clifton before I buy?

    How long carbon tubes do I need to purchase for the copter to be able to run 15" props?

    Maybe this thread has gotten a little out of hand =)

    • Hampus:

      Its all in the post (#182) that I referenced.  Not only does it give you the sizes of the tubes, it also tells you how long to cut them. 

      I've not used those particular motors, so the only thing I can say is your results may vary.  Just google them and see what others think about them, that's what I do.. ;-)

  • Is your first power module from HK too?

    I had similar problem with incorrent measurents too. My PM showed more than 1V difference. The problem was caused by bad wires(!!!) from PM to PX. I measured wire resistance and it was around 1 Ohm.

    • Thank you! That was actually not a bad thought since both of my HK PM's behaved exactly the same way, but it turns out that wasn't the issue. The voltage is totally correct till when the current and throttle gets too high, up to 75A and the voltage just drops. 
      It is in my opinion that the Hobbyking Power Module is underspecced and can't even handle 75A and at this point the readings get totally off. I have ordered a AttoPilot 180A Power Module instead.

      I'll get back to you.

      2015-11-13 16-56-24 74.bin.log

      • Hampus:

        I just looked at your Nov. 13th log, and it is NUTS!

        You said you do not have this problem when the camera and gimbal are not onboard, and I'm wondering what brand of gimbal, how much does it weigh, how do you have it connected electrically, what camera are you using, and how much does it weigh?

        Oh, and I almost forgot, how much does the aircraft weigh with the battery and without the camera and gimbal?

        • It weighs 4,5kg AUW with gimbal and without 3kg. It all has to do with how much throttle I apply.

          What do you mean with NUTS? :D

          • By  NUTS, I mean its crazy...

            I really hate to say this, but your problem is when you have the camera and gimbal mounted the aircraft is overloaded.

            To lift off and hover, each motor/prop combination has to make at least 900 grams of thrust.

            Looking at the manufacturer's test data for your configuration (4S, 13" props), that puts you above 65% throttle, and hover current is probably around 40 Amps.  This testing is done on a bench in a static environment, and I'd wager your actual throttle position and current draw are higher.

            FWIW, conventional wisdom says that a 600mm class hex is good for lifting up to 3.5 kilos, and the limiting factor is prop length. And going 6S is no better.

            I have a 680 that is very similar to yours, except I'm using 4006 740Kv Multistar Elite motors and a 2 axis gimbal with a GoPro style camera and Tarot retracts.

            AUW is 3257 grams.  Hover current averages 24 Amps, and flight times average 18 minutes with a 20% battery reserve.

            So, the bottom line is your hex needs to go on a diet...

            5.jpg

            • Thank you! I suspected this, but it still isn't an apology for the poor current/voltage sensing performance with Power Modules, they simply aren't correct. 
              I would like to extend the arms of my Tarot 680PRO so that I could go with 15" and 6S, wouldn't that be nice? You seem like a nice guy with a lot of knowledge behind you Clifton. Maybe you could recommend me a new setup of motorn/batteries/ESC with extended arms?

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