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


The current

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

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            • You don't have to be an automation engineer to understand Chinese manufacturing philosophy. You have to got here and see it. Or work with them.

              As per this specific issue, I agree. We cannot ignore the overload issue at all. I think that is the number one problem.

        • On the contrary, when you have been working on electronics for as long as I have (Just a tad over 50 YEARS), you pick up a thing or two along the way, and I have a better way.  Its called mathematics, and courtesy of  RCG member renatoa, here's the formula:

          Flight Time = whkg / (1000*R / eff_gw) * 60.


          whkg = battery energy density, in Watt hour / kg, ranging from about 150 for the high C packs to 270 for LiIons. 10C Multistars are 185.

          R = ratio between AUW and battery weight

          eff_gw = motor/prop efficiency, grams per Watt, taken from mfr data.

          This formula calculates an expected hover flight time to battery exhaustion, so to be on the safe side I use 80% and set my failsafes accordingly.

          Also, based on actual flight times, one can determine what the real world eff_gw is as opposed to the mfg's bench test results.  In my case the mfg said the g/w was 9.2 when it is actually closer to 8.

          Courtesy of another member of RCG (who's name escapes me...), I have a spreadsheet that will do the math for you...  Just plug in the battery capacity in mAh, # of cells,  battery weight,  aircraft AUW, and motor/prop g/w.


          • psst im a electrical engineer for Northrup gundum cant say anymore...

            i think i know what im talking about...to much damn weight flying like a idiot.. and battery condition have the factors....

            if you put your faith in electronics you are a fool.. this guy clearly has to diag the situation land and see what the voltage is..

            you can have voltage without capacity.. you do know that right..... you can have 12.5 volts and the minute you fly it drops thats voltage drop thats bad cell thats bad batteries thats cheap cells from china.. china is a crap shoot you can get great stufff or you can get the crap.... end of story... look where 3dr makes its stuff.. MEXICO.. THERE FACTORIES ARE IN MEXICO

            there is no standards  they buy parts from china and assemble them i mean come on....dont brown nose china 

            dont put your faith in electronics use the time method its the only acruate method.. thats why radios have timers on them... any good radio does.... the readings from pixhawk and from these sensors isnt fast enough the downlink it send to mav link is slow so your getting a best guess not a spot on accurate reading aka real time.... ramp up ramp down.. your getting a 12.5 11.5 10.5 depending on how you hit the throttle.. you cant calulate unless you hover.. when you hover then switch to flight then hover.. your readings fluctuate...... thats why gliders and planes fly for longer because they have 1 motor 1 prop  and there not all over the throttle they dont need 50 % thorottle to keep afloat quads do....

            so these sensors are a  best guess..... you average 3 times and get a standard for that battery capacity you use..

            i fly a 250 mini racer i use 1300 and 1800 i get 10 on the 1800 but i fly for 7   

            i get 6 or 8 on the 1300 i fly for 5......

            time to return and land....

            he needs to determain if its a battery issue or a pixhawk issue its probably the sensor... mine does the same thing reads within 1 min it hits the stupid fail safe then returns with 90% left in the pack...

            so what i do i disabled that feature and fly on time and common sense.....

            • Thank you for joining the conversation Wyatt!

              Well I seriously doubt that the batteries is the problem but just to make sure I tested with my friends brand new 4S 5000mah 70C batteries and the problem is still the same..

              I just sent the Attopilot back to the vendor, overpriced shit sensor... I'm thinking maybe I will try this 200A hall sensor: www.mauch-electronic.com 

              Maybe I'll get correct reads with that one!

              • Hampus:

                Its not the sensor, its because the aircraft is over weight, and its more than the motors can handle.

                In fact, until you take some of the weight off, or upgrade the power system, that aircraft is not safe to fly.  At 70%+ throttle there isn't enough throttle left over for the flight controller to use to keep the aircraft stable.  In this state the power system is teetering towards a brown out, and when that happens (and trust me its when, not if) the aircraft will literally fall out of the sky. 

                • Clifton I personally think you are making most sense in this discussion. And whoever is trying to solve this has to remain OPEN MINDED.

                  • that's exactly it Clifton. When RCA any issues it is key to remain open minded. One is full of himself 'I AM ENGINEER" I know everything. The other does not want to accept a weight issue.. how do you resolve anything. lol

                  • Tony:

                    Thanks for the support.

                    Sometimes we get fixated on what we think the problem is, and even in the face overwhelming evidence to the contrary we often refuse to take the binders off.

                    One can only hope that the light will come on...

  • ok heres your issue your batteries or the connection..  replace the batteries and the connector on your copter its probably wiggling loose or not connetinc much during flight on the ground fine but when you take off over time it loosens.. dont use cheap chinese connectors..

    the pixhawk only uses like 50 mah thats nothing.... if your battery suddenly drains you cant blame your pixhawk your motor controllers or reciever why heres why

    the reciever only sends singnal if it pulled that amperage it fry  

    the escs well they will fry or will full throttle you  thats the only way youll drain amps is if you full throttle run aways..

    so its your batteries youve treated them badly there a year old time for new ones.. donty buy cheap ones get name brand ones that are matched...

    make sure when you get ready to fly.. dont charge till the day before aka night before then a top off in the time you go out then when your done rotate them dont charge fly charge fly rotate every 3rd one..... then when your doen put them in storage mode..

    then after a month check to see if there at 3.85 volts a cell if they are there holding storage if not you have a bad cell..

    its that simple battery maintenance and age and how you treat them.. if you full throttle alot race you burn out the packs faster.. 

    • That is some pretty good advice, but it does not explain why the aircraft flies just fine when he removes OVER 3 POUNDS OF DEAD WEIGHT...

      At the stated AUW of 4.5 Kilos, the motors need to develop 900 grams of thrust EACH just to hover.  From the manufacturer's data sheet, that puts the motors at about 70% throttle with a combined current draw approaching 60 Amps.

      The aircraft power system is overloaded, pure and simple.

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