Batteries and total weight?

[loganj13]

Hey all, I'll be buying the E310 hex set in a week or so . BUT, I have been totally the weight of my hex and have some questions.
I'll be running 4S, and I am estimating my setup to weigh around 1700g without batteries...this includes a GoPro and gimbal. Anyways heres my questions: Adding 2 batteries in parallel and legs I havent yet decided on, Im thinking my setup will weigh near 2500kg in total. The E310s are reccomended to have 400g/rotor on 4S, so this will be a bit over, given a very small bit, but this is my estimations that don't include any extra bits like Rx and wires etc. So in reality I have a feeling it will be over 2600kg+. So at that point having it a bit above the reccomended seems like a crappy idea. I calculated that weight with 2 4000mAh in parallel. I'm guessing I should move down to say...7k? (2x3.5Ah) What do you guys think I should do for this? Also, my gimbal motors say they are good for 6-14 volts, and then say 2-3S, but I'm running 4S...Does that matter since theyll be recieving power through a gimbal controller capable of running 4S? Do I need to find different ones? Also, I am planning on getting 25C batteries, do you think thats ok? Thanks for the help guys!

[bigMouse]

That sounds a hell of a weight even for an hexa! You are only running six 8" props, you need to lighten up the design!

Batteries won't last five minutes! 8000mAh is overkill, there is a thing called 'The law of diminishing returns'! when the extra weight of batteries start to cancel out the advantage of the extra capacity!

my gimbal motors say they are good for 6-14 volts, and then say 2-3S, but I'm running 4S...Does that matter since theyll be recieving power through a gimbal controller capable of running 4S?

Regarding the gimbal, 'usually' (so there may be exceptions), Power to the controller feeds through an onboard voltage regulator (gimbal boards generally run at 3.3volts, but the vReg allows an input voltage range, sometimes 2S ~ 4S or more.

BUT the full battery voltage is applied to the gimbal motors (also obviously their drivers, which are on the control board, these can't be regulated easily), and are what limits how many cells you can use (just like there are 3 and 4 s capable escs and motors) also any change in supply voltage will require a change in gimbal pids

btw your quote of '6-14 volts' actually only means 2 ~3S

I am planning on getting 25C batteries, do you think thats ok?

The larger the mAh rating, the lower c you can use


As a rough guide I have two UAV's both quads, ready to fly less batteries 1.5kg, other is slightly heavier, 750kv motors on one, 1000kv motors on the other, both 3S 10X4.5 props 5000 ~6000mAh batteries fine, actually will fly for a short time on a 2200mAh (mainly because the 2200 is a light battery) I have two traxxas 8400mAh batteries and have only flown them twice because I'm getting the same flight time I do with 6000's yet Its visibly working harder to stay in the air with the extra weight

[BIRDS-EYE-VIEW.NL]

Hi,

about the gimbal I most cases I use a regulated switching power supply for this with variable output) This saves weight and the pulses from the brushless controller don't mesh up the other systems onboard. This is the board I use very often 1.5 to 60 volt on the input, 0 to 58 volt on the output with a constant and stable current  of 3 amps. http://www.birds-eye-view.nl/shop/electronic-components/adjustable-power-supply-3-ampere/

About batteries,
Keep in mind that you don't draw much current especially if you hook up 2 batteries in parallel. you then have more the equivalent of 4S 8000mah @20c.
When I check an average copter design then every speed controller/ motor draws a current of 25 amp peak and an average of 12 amps during hover.
Lets say our example copter has 6 motors so during hover you will draw 6x 12 amps= 72amp Since you have 8Amps in your battery you have to divide battery/60minutes/ motor total current= flight time.  in this case 72/60=1.2amp/ minute  Since we have 8 amps available you have to divide 8/1.2=6.6 minutes of flight time (in hover mode and less during flight)
Keep in mind that this is a rough calculations example you can use on every model to calculate the estimated flight time.

So end of story your prop motor battery combo sucks. My own hexa with 10.000mah 3S battery and 2.4 kg (including battery and cam) flies up to 30 minutes without any issue.
If you are interested in the prop/ motor speedcontroller combo I am using please let me know. since your weight is the same you should have the same flighttime.

Wicher

[loganj13]

Thanks, here a little more info about my setup. I will ACTUALLY be running 9.4 IN props, not eight.
The E310 is a DJI system, and the reccomended weight per motor is for hover. On 4S with the stock 9.4x5 props, they reccomend 400g/motor=2400g total. This system also has active breaking, and single strand winding, which are reported to make it much more efficient. Yes I intend to run two smaller 4S batteries in parallel, mainly because seemingly all 4S batteries upwards of 5000mAh are in the 40-80C range, which sound like will be WAY more C than I'll need (right?).
I redid my calculations, and think my setup will weigh a little bit less than I thought, so it should be right around 2400g total (with the two 370g 4k 4S batteries.)
The E310 is the much improved version of dji's e300, which Ive heard great things about, and was going to buy. DJI reccomends 400g/motor on 4S with this system, and judging from thrust tests of the less efficient E300 system, their rec. is on point.
Heres a bit of data I am losely using to judge:
E300 motor and stock dji prop 9.4x4.3 on 4S: 50% throttle=357g/motor (their rec was 350g) at 16.35 volts, and had an amp draw of 2.97 amps! The newer props are 9.4x5.0 so they will have a higher A draw at 50%, although I'm not sure by how much. Assuming some of that cancels out with the great efficiency of the newer system, I'll say a pretty darn high estimate of 5A/motor at 50%. My system weighing near the rec. 2.4kg, hover will be almost exactly 50%, and I'll mostly be doing filming in ATTI mode. So, lets say avg throttle with hover and movement is 60%, (again, a relatively high end estimate.) The A draw of the less efficient E300 system went from 3 to 7 when going from 50 to 75%. Using a similar parabolic curve, a guestimate of 6A avg draw seems reasonable to me, with these high, likely larger than actual estimates. Does this all sound realistic or atleast right math-wise to you guys? So then with 6x6A from lift systems, I dont have an FPV system planned for it yet (I know , lame) the rest of my setup should barely draw anything, and the gimbal shouldn't draw more than a few Amps, (total guess, anyone with more info care to share:)? So then I'd have an estimated avg A draw of 40ish. Doing the math the same quick way as BEV did, 40A/60min=.6667amp/min then 8A/.6667A/min=12 min, save 20% and its around 10.5 minutes...This isn't terrible, and I'd be ok with that. But with those estimates, im just around 2.4kg which is nice and it should fly well on the 9.4x5 props. BEV ya I'd be interested in hearing what setup you use, but unfortunately, I'm a highschool sophmore and am basically...broke  So I'll be sticking with my setup, since I've designed it myself to 3D print  and I cant really afford to try another...
As I said, I felt like the estimates I made above seem like they were on the higher end, (ie the avg thrust probably lower than 60%) and I think the real results are likely to be lower. Anyways, I ran the same thoughts on bat. size vs my weight with a guy who owns a multirotor repair company, and seems to be a very experienced flier like you guys. He said it sounded good, but I wasn't sure (this was before I did the math above) so now I'm wondering, does what I said make sense to you all? Again, I'm a highschool student, I've only been doing this for a few months, so I won't be suprised if I was wrong. Also, the guy I talked to said he'd even send me a few 4S batteries of that size, used but free ! (Probably plenty of this stuff lying around if you run a repair company Anyways, what are everyone's thoughts on this now that I've posted some more info? Thanks again for the help! -Logan

[loganj13]

EDITS+SUMMARY OF ABOVE:
Someone JUST posted some info about their first flights with E310 system. According to their OSD, the Amp draw in position lock hover was 15.5-16A, on a quad running the E310 system and weighing exactly 1750g. This was on 4S, and the reccomended weight/motor is 400g, so they were a bit above it. Because of this, I am considering the slightly higher than 50% throttle for their hover roughly equal to 50% or slightly less throttle for hover+horizontal movement of the same system. SO: closer to 4A/motor. Which makes it even better 4x6=24+1A gimbal+FC draw=25A total avg draw. 25A/60min=.41667A/min, 8A/.41667=19min, 80% rule (what voltage should I set the safegaurd to?)=15min of flight time, which sounds good to me. Btw, the E310 setup is 9450 props, 960kv motors, 20A escs. I am NOT using the way higher kv motors like I was considering, or 8in props, so the avg amp draw per motor shouldn't be close to 12A...

[bigMouse]

Personally I'm not a DJI disciple so won't comment on their sales crap! and would suggest take any of their promo spin, with a pinch of salt!

single strand winding, which are reported to make it much more efficient.

Mis-information! I'd argue that but its a bit off topic! They are either woffling or know little about electronics.

Yes 15~20Amps at hover sounds reasonable for something weighing that!

Don't forget that increasing 3 to 4S is increasing power (Ohms law) so same current will supply more watts.

[loganj13]

Ya I'm wary of DJI as well, they do kinda suck.
For example the Naza Lite is the exact same thing as the Naza M v2 but just crappier software. Luckily I hacked mine up online And the whole naza series is missing a SAW filter, which is a basically standard part to a gps puck...
But ya, I'm not taking their info at face value, especially since they dont provide any real thrust data, but the math makes sense I think. 25A seems like a relatively acceptable A draw for a hex of that size. I should stick with 25C for the batteries right? Would it be risky going down to 10C, which is tempting because its so much lighter...Well ill see what I can test out!

[bigMouse]

With the variation in battery quality I'd be very wary of going below 25c, for anything other than say vtx or R/C Tx batteries.

[BIRDS-EYE-VIEW.NL]

If you want to know the max C you need. then multiply the battery capacity to the C value. for example 5000mAh x 20C=100000mAh or 100Amps So if your maximum (combined) current from your copter is less then 100Amps in total then you are good. If not you need higher C value and/or more capacity.
One last word about C keep in mind that lots of Chinese suppliers advertise with peak values and not with constant values. So always check what current you can draw continuously and in peak.

[Mancini]

C value in Zippy packs is bullsh...t.BTW.

[bigMouse]

Not a zippy fan at all, at all! Nanotech's FTW

[loganj13]

Zippy packs have bogus c ratings  ?? Thats what I was thinking about getting. So my avg amp draw is around 25A, so 2 4000mAh batteries, each 25C, so 25Cx8000= 200000mAh=200A, so even if the Zippy packs are BS ratings I should be fine if its lowet than advertised right? It claims 25 continuous, peak 35. Even it is closer to 20C or something, I should be fine, should I get different ones, or are those ok?

[BIRDS-EYE-VIEW.NL]

Try to find lower C rated batteries. 2x 25C 8000 are adding to much extra unnecessary weight to your platform. On my website I have lower C rated batteries for this purpose. and if you need even lower C ratings and/ or more capacity then we can custom build them for you. Already delivered 5c 25000mAh packs to an other customer.

Wicher

[loganj13]

Thanks, BUT a super nice guy just sent me an APM2.5 w/ gps, 2014 3DR X8 frame, and 4-4S 35C 5000mAh batteries, for free! So, I'll probably just run one 5000mAh battery at a time, and MAYBE ill try 2, depending on their weight. Also, from what you were saying, does the C double when you put two identical batteries in parallel? If each battery is 25C, then in parallel is it 50C since its drawing half as much from each battery at a time? Thanks!

[bigMouse]

That's good news! That should be ideal for you!

does the C double when you put two identical batteries in parallel?

C rating is nothing more than a number! It's ( C rating = max discharge/mAh rating) so intrinsic to a particular cell!

Your 4S 35C 5000mAh batteries as an example:

2 in parallel would = 4S 35C 10,000mAh

2 in series would   = 8S 35C 5000mAh

So, I'll probably just run one 5000mAh battery at a time, and MAYBE ill try 2

Two 5,000mAh batteries will likely weigh more than one 10,000mAh one.
But on the other hand, two in parallel will have roughly half the total internal resistance of each individual pack, this will in effect allow more discharge amps. So likely to be the more efficient setup, Whether actually noticeable or not would need to be seen!

From this you can probably figure out that the C rating won't change because the C rating and internal resistance is closely tied together!
internal resistance of any cell will more or less stay the same, yes will drift with age and temperature. Actual values will change slightly even from cell to cell in the same pack! And generally the lower the C rating the higher the IR is likely to be! And the cheaper the battery should be!

All this and I haven't tried to sell you anything!