How to choose battery capacity for longer flight time

Larger battery allows for longer flight time. Unfortunately the increase of flight time isn’t proportional to the increase of battery size, which means you are looking at something like this.

Before we begin, make sure to read the basics of LiPo battery for drones.

flight-time-vs-battery-capacity

As the battery gets larger, the increase in flight time becomes ineffective. Eventually it will reach a point where it just doesn’t gain any more flight time with bigger battery (even lose flight time). This is mainly caused by the weight of the battery. Also note that the heavier your copter gets, the less agile it will be. But some people prefer the stability it brings with heavier weight, some would call it “flies like a tank” :). Apart from capacity, there is also C-rating you need to consider, which I shall explain later.

The trade off between flight time and battery capacity, makes it more difficult to choose which battery should be used, rather than just “pick the largest battery available”. There are techniques you can use to help with this selection task – creating graphs and mathematical model in Excel, which I found really useful when comparing various products of the same kind. I recently bought some 4S batteries for my FPV tricopter, I will use this as an example. This technique should be useable for any multicopters, including the 250 mini quad.

Talking about Batteries, here is a tutorial on how to do LiPo parallel charging.

List All Batteries and Create Graphs

First, list all the batteries with different capacities, brands of the same cell number. You can include their weight, price, etc in your table. For example I was looking for 4S lipo battery for my tricopter and here is the table I created.

Max Current Draw and Battery C-Rating

It’s important to note, that the batteries you listed can supply enough current for the motors. Max current supplied by the battery can be calculated by this formula:

max current = capacity * C-rating

First, work out what would be the possible max current draw from your motors. I usually just look at the motor datasheet, which should tell you what the current draw is at 100% throttle, times number of motors, and add some margin for other electrical parts, and you have the possible max current draw from your quadcopter.

My tricopter has a max current draw of around 30A – 35A, and all of the batteries below meet the requirement.

Listing batteries and data

Battery-table

From these data, you can create some very interesting and useful graphs, for example I usually do

  • Density, which is capacity per gram (= capacity / weight), and
  • Value, which is capacity per dollar (= capacity / price)

battery-density-graph

battery-value-graph

From the above graphs, if I am only going for best performance and not worry about the price, I would definitely go for 2650mah, 3000mah, or 3300mah. Also 4000mah might be a good choice too due to its outstanding value.

These graphs tell you some insights into which battery has the highest price/performance ratio, but it doesn’t tell you whether this is the best battery for your RC aircraft, quadcopter or tricopter. To do that, we need to create a mathematical model.

Build Mathematical Model to Estimate Flight Time

This is actually pretty fun to do. By using this model, you will be able to calculate the flight time of any battery. All you need to do is to put in the data of that battery in the excel spreadsheet. Of course, this is only an estimation, but it does give you an rough idea what battery to go for, and save you from spending too much money and time to try each type.

First of all, you need to get one battery first, and collect data using it. Basically the data we need is flight times under different loads. You can of course collect some other data as well to help you identify what is the max load your multicopter can take, for example, the throttle value, current etc.

In my example, I used a 2200mah 4S Lipo Battery as a reference, and tested the flight times under different load weight (0g, 110g, 220g, 340g, 405g, 515g – all these weights are physical items I can find in the house that’s why the uneven numbers). This is the data I collected from 6 test flights.

Mathematical-Model-for-quadcopter-battery

I always land the tricopter when the voltage alarm beeps, which is when the voltage reaches 3.5V per cell. The column “Actual Capacity Used” is not really needed, but I collect it just to make sure my data is valid. I got that from my charger, when I charge it fully at 4.2V per cell, I know what capacity was used in the previous flight. I then work out “mah / second”, which is the speed of power consumption, and we can draw a graph from this.

battery-usage-vs-load

The good thing about Excel is, it provides an equation from a few dots on the graph. This is probably should not be a linear relationship, but the battery weight falls within this range so it’s close enough for me.

So here is the model. “Cap at 3.5V (86%)” is the effective capacity that can be used during a flight. I am making an assumption that the voltage drops down to 3.5V when 86% of battery capacity is used. “mah/s” is calculated from the above equation, we can work out the mah/s for each battery, depends on their weight.

Mathematical-Model-flight-time-estimateion

And now the estimated flight time is roughly equals to effective capacity divide by mah/s. For example for the 6000mah battery, the effective capacity is 5160mah, and the speed of power consumption is 5.75mah/s, so the flight time would be 898.16 second which is nearly 15 mins.

Mathematical-Model-for-quadcopter-battery-flight-time-VS-load1

When I worked out all the flight times, I found this interesting relationship between size of the battery and flight time. That’s exactly what we predicted at the very beginning.

flight-time-vs-battery-capacity1

That’s the analysis I always do when buying batteries. I made a lot of assumptions above, so also do your research on the flight time, ask people for their experience, to verify your theory.

Let me know if there is any mistakes in the method, or any better ideas.

59 thoughts on “How to choose battery capacity for longer flight time

  1. Simone

    Hi Oscar,
    I read your infos about LiPo batteries and I would like to share with you my difficulties.

    I am building a quadcopter with these specs:
    X conf, 500mm aluminium frame;
    4x Flycolor ESC 20Amp;
    4x MultiStar motor 935KV (15Amp Max);
    Propeller 10×4.5;
    Weight 1250g.

    I had bought a 3S LiPO 5200mAh 10C (Discharge max 20C). I am just doing some stabilization-test but the battery already last short and it seems that one cell is ruined (the voltage level is always lower than the other two). Moreover, I can not charge it above 11.3V.
    Did I choose a wrong battery?

    I am looking for a new one, founding the list below. Which one would you suggest?
    Turnigy nano-tech 4000mah 3S 25~50C Lipo Pack
    Turnigy nano-tech 4000mah 3S 35~70C Lipo Pack
    Turnigy 5000mAh 3S 20C Lipo Pack
    Turnigy 5000mAh 3S 25C Lipo Pack

    Is it correct that the 5000mAh should last more than the 4000mAh even with higher C-rate?

    Thank you very much for you help!

    Reply
    1. WeiWen

      Hi Simone,
      Of course your battery will short !!! your battery can discharge maximum 52A only while your motor draws 60A.

      About your new battery…
      All of them can be used for your quadcopter.
      The c-rate WILL NOT affect the flight time. So both 5000mah have same flight time and of course the battery will last longer than the 4000mah.

      Reply
  2. Hari Prasad B

    Hello,

    i want to build quadcopter with this parts:

    Motor specs-
    A2212 / 13T 1000KV Brushless Motor Outrunner

    80% max efficiency
    4-10A max efficiency current
    No Load Current: 10 V : 0.5 A
    12A / 60s current capacity
    2-3 Li-Poly cells
    Suitable for airplane, aircraft, quadcopter.
    Model: A2212
    KV: 1000
    MAX Efficiency: 80%
    MAX Efficiency Current: 4-10A (>75%)
    Current Capacity: 12A / 60s
    No Load Current: 10 V : 0.5 A
    No. of Cells: 2-3 Li-Poly
    Motor Dimension: 27.5 x 27mm
    Shaft Diameter: 3.17mm
    Weight: 48g
    Package Weight: 59g

    ESC-
    Wolfpack 30 Amp ESC

    Output: Continuous 30A, Burst 40A up to 10 seconds
    • Input Voltage: 2-4S Lipo, 6-18 cells NiMH
    • BEC Output: 3A / 5V (Switch Mode BEC)
    • Refresh rate of the throttle signal: 50Hz – 400Hz
    • Max Speed: 210000rpm for 2 Poles BLM, 70000rpm for 6 poles BLM, 35000rpm for 12 poles BLM
    • Size: 73*26*8(L*W*H)
    • Weight: 38g

    Flight controller – Naza M lite

    AUW-1500gms (FPV included)

    Battery ?
    C rating-
    mAh-

    Should i go for –

    Orange 2200mAh 3S 30C/60C Lithium polymer battery Pack (LiPo)

    Or

    Orange 3000mAh 3S 30C/60C Lithium polymer battery Pack (LiPo)

    Or

    Orange 5200mAh 3S 40C/80C Lithium polymer battery Pack (LiPo)

    Battery Charger ?

    I have this one already
    SKYRC IMAX B6 CHARGER

    Operating voltage range: DC 11-18 Volts
    Circuit power: Max. charge power 50W
    Max. discharge power 5W
    Charge current range: 0.1-5.0A
    Discharge current range: 0.1-1.0A
    Current drain for balancing Li-po: 300mA/cell
    NiCd/NiMH battery cell count: 1-15cells
    Li-ion/Fe/Polymer cell count: 1-6cells
    Pb battery voltage: 2-20V
    Net weight: 277g
    Dimension: 133x87x33mm

    Battery ??????????

    Reply
    1. FlyNfool

      @Harry Prasad,

      I would suggest starting with a ‘good old standby’ cheap battery like a Zippy 5000mAh 3S 30C. Your max current draw with 4 of those motors is only 12×4 = 48amp, and that is full throttle max load. At 1500g all up including battery you should see around 9 minutes of flight drawing down to 10.6 or 10.7 volts. I built a 450 quad (cheap ebay RHD 2212-920kv motors, 1045 carbon fiber props, ZMR450 frame, SimonK 30a Mystery ESC, M8N GPS, pixhawk controller, SiK telem, FPV) that is 1375g including a 3S Zippy 5000mAh 30C, and I get 10-12 minutes of smooth, easy “camera platform” flying on a loiter or position hold mode. 7-8 minutes if I fly it hard in acro mode.

      Your motors are 1000kv, I would suggest a 9″ prop instead of the 10″ that I run. Be sure to check/balance all your props. If you’re new, get plastic/nylon props. After you get the hang of it, switch to carbon fiber props. You’ll notice a difference in sound and response…and a little in efficiency.

      I use imax b6 chargers too.

      Good luck, happy flying.

      The FlyNfool

      Reply
  3. kunal gokhe

    HI
    i am making quadcopter using kk2.1.5
    motor A2122 1400kv max current 16A

    THEN
    3s 3000mah 20c battey is best

    Reply
  4. Yaniv

    HI. I have the robocat racing drone. (Got it as a kit)
    I have a 20amp esc x4 (80amp total)
    The only thing I have to understand is what battery should I use.
    I tried 1200mah 11.1v 25c
    Won’t work good…
    Now I ordered 2200mah 11.1v 35c
    Will it work?

    Reply
    1. Gairik Biswas

      Battery capacity * C-rating rate MUST be ,more than motor current draw otherwise your battery would deteriorate very quickly. Try using larger props. If you have a heavy drone then use low KV motors as they provide more torque. My Flying 3d x8 is about 800g and uses 935 KV motors.

      Reply
  5. Sagar

    Hi Oscar.
    This is one of the best explanations that i have come across so far. Really useful and informative for beginners.
    I’m trying to build a micro quad around 100-150g. Can you suggest the optimal battery, motor’s and prop that I can use.
    If you can give me the details i would be really glad for your help.
    Thanks.

    Reply
  6. EzMe

    Hi Oscar,

    Thanks for this article. It really helped me forward! Could you please add a link to you excel sheets?

    Thanks in advanced!

    Reply
  7. RITIK

    Hi Oscar,
    i have a2212 brushlees 1000kv motor with the following specification:-
    Specifications:
    – A2212 1000KV
    – RPM/V :1000
    – Stator Diameter(mm) :22
    – Stator length(mm) : 13
    – Stator Arms(mm) : 12
    – Magnet Poles : 14
    – Motor Winding : 22
    – RPM(KV) : 1000
    – Idle Current(A) : 0.55/8
    – Max Current (A) : 17
    – Max Power(W) : 190/3
    – Rotor Dia(mm) : 28
    – Shaft Dia(mm) : 3.17
    – Motor Length(mm) : 28
    – Overall Length(mm) : 42
    – Biggest Thrust g/S : 1200/4

    i want to know that how much mah & discharge rate battery would be required for this motor where i have 30a ESC

    Reply
  8. puvan

    i am using 1200 mah for my tricopter,

    motor: 1200 kv. max current 16 A and for 3 motors 48 A

    But battery can give only 30 A,

    is this is the problem or i can use it,

    my copter is just rotating on the ground and not fllying. all the setting i have done correctly. i am using kk 2.1.5 board

    Reply
    1. mus377

      Hi, Puvan, im not sure about this. try 20A/30A esc or change bigger props. Might be esc was very low and your drone very heavy. My setup drone X525 quite big drone around 600gram to 1.5kg/2.5kg can lift very fine with 3S 1500mah but respond quite slow also to lift slow too, and drain fast. My ESC 30A. Duration test no camera 3s 2200mah 30c old battry around 5minutes / New 3s 2200mah 30c 11minute / Parallel New 3s 18/22 minute. “Guest what near 30Minutes”

      Reply
    2. Kenny

      Hi puvan,
      Uh… thats a negative, ghost rider… your batt is taxed. If you are running 3 motors for a total of 48 amps and your batt only delivers 30 amps, major problems WILL happen. Lets add it all up… 48 amps for motors, a few amps for the FC, a few amps for the radio Rx, some “head-room” usually 5 to 10 percent… So far, we have roughly 52 amps for basic gear, 5 amps for head-room, for a total of 57 amps. I would round that up to 60 amps. Your battery should be rated to put out at least 60 amps continuously… NOT peak rating. For example: 1300mah 45C to 90C. Move the decimal over to the left 3 spaces to convert mah to amps like this: 1300(.0)–> 1.3 amps. Now multiply 1.3 x 45C. The first number in C rating is constant rating, second number is peak and the battery CAN NOT run that much current for very long. So we get 58.5 (amps) and 117 (amps). So now we know that the example batt will deliver up to 58.5 amps continuous and 117 amps peak, for extreme manovers and punch-outs.

      ALWAYS make sure your battery can deliver more amps than you can use. I like to look at my flying and figure where I spend the most time at what throttle position and either bench test motors and props I am using or look for a data table online and figure out what my motors are pulling at said throtttle position, then do the math as we did above and match a battery with the first, low C rating equal to or larger than the amps I calculated.

      Blue skies, Brother and good luck

      Reply
  9. ketan tejani

    Hi Oscar,
    We are use 8, 1300 kv bldc motor for multi copter and its maximum current rating is 50~60 amp and produce thrust is 1860~2400 grams, so how many mah battry is suitable for long flight time?
    Pleas riply as soon.
    Thank you.

    Reply
  10. Kiran

    Hi Oscar I am building my first quadcopter.
    I want suggesion in using components like propelers,frame,esc,motor,battery.
    mainly I want to build flight controllers,transmitter and reciever so please help me by sending details needed for that.
    I am unaware of most of the things so please tell me details.

    Reply
  11. Arash

    Hi Oscar,
    I think there is a mistake on your choice of batteries, you mentioned that you prefer performance rather than the price, but the batteries you chose (2650mah, 3000mah, or 3300mah) have more density and are cheaper than other batteries in the list. it seems like those with higher capacity and less weight are more expensive.

    Reply
  12. Romain

    Hi Oscar,
    thank you very much for this detailed and usefull article and more generally for your awesome blog. I love it ! One of the best I know so far about quadcopters and FPV… even though I am really new to hit as I finished mounting my first quad last week :). Nethertheless I spent several month diggingintensively on many forums, blogs and websites before buying my forst quad.
    I built an Emax Nightawk 280 with 12A BLHeli ESC, Emax 1806-2280kv, Naze32, FrSky Taranis X8R (coming with the Taranis, but will most probably change for D4R or X4R), Gemfan 5030 props, 1350mAh 3S 45C lipo, Skyzone 3D camera, Skyzone SK201 dual video transmitter, for a total of 550 g (battery and HD AEE cam included). My problem is that I got a really really short flying time of only a couple of minutes (and when I say a couple… I really mean a couple : 2 ) and that is when removing the AEE camera. I guess it could come from the FPV setup but I was wandering if you had an idea of what could be the problem and if you could cue me on how to solve it. I guess using a 1800 mAh lipo would help, but do I need to choose one with higher C ? I might switch to a more classical FPV setup to try if it is the problem. Regarding the specs of the FPV, it should not draw that much power (5v/0.5A, 1.6W for the camera, 12V/1.5A 7.5 W for the Tx)…
    Any idea ?

    Reply
    1. Oscar Post author

      What’s your total weight of the quad? I think you might want to try 6030 props with might give you a bit more efficiency.

      Reply
  13. Jesus

    Hi, i am actually a noob at this so i am asking myself how to build a quadcopter, i just got the motor antigravity 4006 T-motor, prop eller 15*5″, ESC T-motor AIR 20A, and a PDB with max 100A, but i am lost about what battery should i get? somebody could help me this is a project for a class so, i am kind of lost and almost out of time, i have like a month or 2 to do this. i would be really greatful if someone can help me out!

    Reply
  14. vaibhav Patil

    “Hi Oscar” I wanted to make a hexacopter which will have around 3-5 kg of payload and flight time around 30 min,so for these purpose which batteries i can use ?

    Reply
  15. Peter Liwyj

    Hi Oscar

    I am building my first multirotor. I 3D printed all the parts except the aluminum booms. It it a T shaped tri motor. Without the battery it weighs 506 grams. The motors are Multistar Turnigy MT2213-935KV with 10×4.5 props. The ESC are Afro racing 20A Linear speed controllers, It has a KK Mini flight controller and an Orange 615X reciever, I ordered a Multistar High Capacity 3S 4000mAh Multi-Rotor Lipo Pack. The battery weighs 244 grams and is 10 C. Is this OK? I plan to get other batteries too but I want to know if I Have selected the right size. Here is a picture http://i287.photobucket.com/albums/ll144/Peterthinks/130_0492.jpg The motors are 545 millimeters apart. If you ever want anything 3D printed send me an email I will do it for you, I appreciate the time and effort you have put into making this information available.

    Peter

    Reply
    1. Oscar Post author

      Very very nice Peter :)
      But your choice of battery is a bit too low in C rating.
      Not sure exactly how much current your motor/prop will draw without testing, i guess around 15A on 3S at 100% throttle? so max current is 15*4=60A.
      For 4000mah you are looking at 60/4=15C

      Reply
  16. Andreas

    Hi Oscar

    Im about to build a quadcopter but Im not really sure about what parts to use… The man question Is If The PCB on the tarot 650 sport is enough or do i need one mor externa? Also how i get it to works with The motors ive choosen and The flight controller.. since the motors need 22.2V and the flight controller, gps, receiver and so on is about 5V
    It would men alt to me If you would like to help me with this!

    Heres the parts:

    Motors: banggood.com/Tarot-6S-380KV-4008-Brushless-Motor-For-RC-Foursix-roter-Multicopters-p-936812.html

    Frame: banggood.com/Tarot-650-Sport-TL65S01-Quadcopter-With-Retractable-Landing-Gear-p-957351.html

    Flight controller: banggood.com/Tarot-ZYX-M-Flight-Controller-GPS-Module-PMU-Module-USB-Module-ZYX25-p-980863.html

    Esc: banggood.com/Hobbywing-XRotor-Pro-40A-Brushless-ESC-DEO-2-6S-For-RC-Multicopters-p-992316.html

    Battery: banggood.com/ZOP-Power-22_2V-8000MAH-30C-Lipo-Battery-XT60-Plug-p-990752.html

    Cheers!

    Reply
    1. Chris Barth

      Andreas,
      The PCB on the 650 sport will be just fine. My 650 sport pulls almost 80A @ 15V at full throttle, never had a problem with the built in PDB. Trust me full throttle is rarely needed. Since your using higher voltage its even better, less amp draw.
      Everything you list looks fine. The X rotor ESC’s are great, one of the best on the market. Very fast switching speeds and strong dynamic braking. Big plus that its 6s capable.
      You failed to mention your prop size. Thats the critical component. Id imagine a 15×5 prop would get close to being right.

      Reply
  17. tharinda

    i am expecting build quad copter with below mention items.what is the suitable batter for this.pls help me.

    NEW 4Set 1806 2300KV Motor &Simonk 12A ESC For 250mm QAV250 FPV QuadCopter Mulit
    CC3D Openpilot w/case Flight Controller 32 Bits Processor FPV QAV 250 400
    T Plug Power Distribution Board/ESC for RC Quadcopter APM PX4 New
    Hot Flysky FS-T6 2.4GHz 6CH Mode 2 Transmitter W/Receiver R6-B for RC Multirotor
    2 Pairs 1045 Propeller 1045R 10×4.5 CW/CCW for Quadcopter Multirotor

    what else do i need???

    Thank you

    Reply
      1. Viktor

        Hi Oscar, I have a UDI U818a quad that came with a stock battery which capacity is 500 mAh, but that didn’t provide much flight time. So I watched a video on YouTube where guy used a 1200 mAh battery instead of 500 mAh and managed to fly it almost double the time. I bought a 2000 mAh battery with the same voltage as a stock battery (3.7 V), and it’s a bit bigger in width and weighs two times (30g approx.) but that doesn’t quite matter. Recharged it with the stock charger that came in the box until the red LED turned green which means it’s fully charged. Then made sure the transmitter batteries were fully charged which are still brand new and not very used. When I turned it on and after gradually rising the throttle up to about 65% to lift it off the ground it did’t even lifted and it just shut itself down. I soldered a little power switch via one wire leading to the battery connector so I don’t have to unplug and remove the battery in order to turn it off. I turned it on again and did the same thing several times it did’t lift off the ground. I don’t know for sure should’t I left it charging a bit longer regardless of the green light or does it have to do with a tipe of charger itself. Any suggestion? Regards!

  18. Zewill

    You mention in your article that you stop when the alarm says 3.5v … I always heard that discharging past 3.8v was bad… ? Any input? Thanks!

    Reply
  19. alex

    hi Oscar I’m making a quadcopter that weights about 1300g without the battery. I’m using HobbyFans 30A ESC, 2212 920kv motors with 9443 props, and a kk2.15 flight controller. what battery would you recommend I start with?

    Reply
    1. epsilon

      Hi Oscar

      I’ve exactly the setup you ask about, and 3S 5500 is to heavy (fly only 3 minutes and probably the ESCs get hot). I’ve found that the 3300 mah is very good. Flight time is about 10 minutes, and then low-batt warning initiate return to home. I’ve set the redundant battery capacity for 2 more minutes, so you will have about 12 minutes with a 3300. Probably 4000 – 4500 will be a good choice to, but the 5500 (470 grams) is to heavy.

      Reply
  20. Wasantha

    Hi,

    I have Sunnysky 2212 980KV mortors, but nothing else with 25A ESC’s. My motor spec says Max continues current is 15A/30S. Recommendation is like 2200mAh 4s battery. I would prefer bit running time. How do i find the best possible battery?

    When I calculating the max current, what C rating value we get in to consideration? Burst current or constant? Please help me.

    cheers

    Reply
    1. Oscar Post author

      From the information you have at the moment, you can only decide on the C rating, and roughly the capacity range you should go for.
      C rating depends on your total max current draw, and that can be determined from your motor / props combination you are going to use. you have not specify what props you want to use in your question.

      Reply
  21. Kevin Smith

    Interesting read. You didn’t state what battery you would choose and why at the end. I’m curious to see what you picked based on the data. Also, I’m not sure I follow your statement on mah/s VS Load as the weight of the 6000mah battery isn’t in that range. Also, you lost me on the Flight Time VS Load graph and how that correclates to the 6000mah batter you were basing some of your numbers on. I see on the Flight Time VS Bat Capacity that the flight time starts to level off based on the battery size. I assume this is because of the weight of the battery and thus anything larger than the 6000 mah would be useless as you would see no increase in flight times.

    Reply
    1. Oscar Post author

      i went for 2200mah in the end :) cheaper, and more efficient. I wasn’t looking for super long flight time anyway :)

      Reply
  22. Ryan

    Thank you so much for all of the help that you have been providing. Here is my rig so far:
    Lynxmotion Quadrino Nano Flight Controller- .64kg
    Tarot FY650 Quadcopter frame .47kg
    Motor/ESC/Prop Combo- EMAX Quadcopter 550mm combo- 810kv/ 950g thrust per/1045prop/20A continuous 25A burst ECS/ 440g or .44kg weight for all 4 Rated for either 2S or 3S battery. I believe I want to get a battery that can push 100A or 25Ax4.

    I am looking as 3s batteries in the range of 5000-5500mAh for longer flight time. What is the recommended battery for this rig? Will the flight controller limit the battery discharge so I do not burn out my ESCs? For example a 5000mAh 20C will give me my 100A. Should I still look for a higher C rating? I have created some Excel charts as above and the results are very interesting indeed.
    I am trying to make this rig a stable platform with which to shoot video with a GoPro/gimbal which I believe is another 370g or .37kg.
    I believe that my weight is at just below 2kg before the battery. Feel free to tear apart any of my calculations.
    Please recommend:
    Battery
    Battery Charger/balancer
    Transmitter
    Thank you

    Reply
  23. questech

    Hi Oscar

    I hope you don’t mind this long post, but I think you might enjoy helping me :)

    I am prototyping an Octocopter and I have a great flying beast weighing in at 40lb with a 10lb payload. It is designed and has the thrust to lift 90lbs.

    Normal payloads are between 8lb – 15lb for this unit and it is designed to take a real punishment.

    The problem, as you may guess, is keeping it in the air.

    I am using a variety of test Lipos ranging from 6S 6000mAh 50C to 6S 15000mAh 30C. These batteries came from China and I don’t trust that they were rated accurately, but the weight and size match the basic specs for Lipos in their perspective categories.

    My lipo combinations are: 4X6000mAh – 6X6000mAh – 2X15000mAh – 2X15000mAh Plus 4X6000mAh.

    At full throttle each motor can consume approximately 52 amps at 1150 watts at 8 motors that’s 416 amps at a whopping 9200 watts. That’s a lot for an RC aircraft spanning 1400mm.

    The motors I’m using are very efficient compared to the market leaders, but give me the power I can’t get from T-Motors or Avroto motors.

    The actual problem is that I can’t get all of the mAh out of the Lipos. Hovering with a n 11.5lb payload is at 60% throttle and consumes 19amps per motor. No heat at all and everything functions fine. Without the payload the Octo weights in at 28lb and it hovers at between 40% and 55% throttle consuming about 14 amps.

    I can’t tell you the exact amperage because I am only getting the peak amps at the end of the flight, I have to design a better solution so that I can get real-time data, but I’m also using my motor bench test data here to give a good approximation.

    During the flight, with or without the payload, I start out at 25V and over the course of the flight the voltage drops off in a nice gentle curve, no erratic behavior. I land when my transmitter telemetry shows 21.3V. As soon as I power off the motors the voltage goes back up to 22.5 volts and within a minute the voltage is at more than 23V.

    I am getting very short flight times. I should be getting at least 16 minutes but I’m getting 9 min. to 11 min. without the payload and only 4 minutes with the payload.

    When charging the mA put back into the 15000mAh rated Lipos is only 7000. The 6000mAh lipos only take about 4000.

    I believe that I could fly longer if I landed after the Lipos reached 21.3 (or even push that a bit) and waited 3 min. – 6 min. Although I haven’t run that test yet, I feel I could get more flight time and maybe drain some more useful current from the Lipos.

    Somehow the Octo seems to be draining the Lipos faster than they can keep up, but once the demand is reduced, the lipos spring back fairly quickly.

    I am no expert, but I know there has to be an explanation for what I’m experiencing… I just don’t know what it is…

    Can anyone shed some light on this for me?

    I much appreciate any constructive feedback you can offer!!

    Thank you in advance… Anthony

    Reply
    1. Sean

      Hi Anthony,

      I’m no expert, but I think that those symptoms MAY be cause by the batteries being overdrawn. Maybe their discharge rating was falsely advertised and is not high enough to keep up with how much power you’re drawing. That would explain the voltage sag which recovers when landed, and would also explain the suddenly much shorter flight times when adding a little more weight (which increases current draw from the batteries). Just an idea anyway.

      Reply
  24. Rishabh

    hi oscar
    i am newbie to quadrotors i have already purchased kk 2.1 board. And i am looking to buy a 450 mm frame to make my first quad, but i want to make a 550 mm quad too and i want to add a cam on it too, my flight time requirements are of 10- 15 minutes, can you help me to select the proper combinations of motors, props ,esc and battery so that i can achieve desired results.And i can use them in both 450 mm and 550 mm quad.
    thank you

    Reply
  25. Igor

    Hi Oscar,
    Currently I am working on my school project and I need to make similar research. I have built quadcopter with total weight 2200g (including battery 500g, gimbal and FPV). Battery: 5000mAh 25C Zippy Flightmax 4s, motors: AX-2810Q-750KV, props: 11×4.7. I also use an eCalc for initial calculation of my setup, but I would like to understand all the mathematical relations on the background in this field.
    Could you share with me an excel file or if you have some useful documentation ?
    Thank you.

    Reply
  26. Mike Rodgers

    Hi Oscar, Thank you for the information. I’m brand new to building quad copters and really want to build one that will get off the ground. :) Anyway here is the materials I have so far: 500mm X-Mode Alien Frame (355g) , Board kk2.1 (33g) , Motor x4 2212 1400KV (188g) , ESC 30A x4 (100g) , Receiver (13g) , Prop’s x4 1045 (11g) Total Weight is 700g without the Battery. The motors call for ether a 2s 3s 2200mah battery. I’m not sure if this is per motor or if it is no matter how many motors I use? It just seems like a 2s 3s is far to small to fly this quad for very long. I don’t want to waist any time or money on buying the wrong batteries. Can you give me any ideas on what I should buy or if you think I have put together the right configurations of parts so far? I also plan on adding other stuff later on in the build. I want to add a FPV set up and GPS but right now I figured I would start off here. Thank you for any help you can give me. Mike Rodgers

    Reply
    1. Oscar Post author

      Hi Mike
      Battery cell count can be determine by the motor you use.
      are you using Sunnysky 2212 1400kv? in that case you will be better off with 3S lipo.
      Capacity wise, 2200mah to 3600mah should be a good range for your build.
      You might also want to use smaller props for this motor. 8040 has the best efficiency, but 9 inch props gives you more thrust. 10 inch is probably too big and inefficient.

      Reply
      1. Mike Rodgers

        I’m not sure if you received my last reply, I wanted to thank you for your input. I finished my build and now i will be ordering the battery and 8 inch props. I’m glad you gave my the information about the props. I will let you know as soon as I get it off the ground. I hope the fact that I was off on the weight about 100g won’t make to much of a difference? I didn’t know that the scale that I used was off by a good bit and the total weight is just over 800g. I will try the larger mah and try other size props as well just to see what works best. Thank you again

  27. nine

    Hi, Oscar, I was getting an average of 18 minutes flying time on my tarot t960 hexa with 2 5400mah tiger lipos In parallel. So thats 10800mah. Is that long enough or should I be getting more? My motors are tarot 5008, 340kv with 1755 props. One more thing, a while ago I flew my hexacopter but the naza low voltage warning appeared after only 6mins on fully charged batteries. When I checked, the other battery wasn’t discharged. There is nothing wrong with my parallel connectors so can you think of anything that might be the cause of only one battery discharging despite the fact that they’re both brand-new and fully charged before the flight?

    Reply
    1. Oscar Post author

      what’s your AUW ? What is the C rating of that battery you are using?
      Have you not got a voltage OSD? so you can check the actual voltage when the buzzer goes off and verify.

      Reply
  28. Nemanja

    Hello,

    i want to build quadcopter with this parts:

    motors – rctigermotor.com/html/2015/Navigator_0206/286.html
    esc – rctigermotor.com/html/2013/esc_0916/85.html
    fc – xaircraft.com/products/superx/

    that quad must have Gopro and video sistem. That is about 3 kg all together.
    what battery should i use for that? What voltage, what capacity…?
    All the best!

    Reply
    1. Oscar Post author

      looking at the thrust data provided by the seller. 3KG of weight, that’s about 750g of weight need to be handle by each motor. Taking into account the efficiency lost, I would make it 900g. Assume you are using 17inch prop, you should be able to hover at less than 40% of throttle, current draw should be less than 5A for hovering. assume half of the time you are using 75% thottle to fly around, and the rest of the time hovering, average current draw would be about 12A. (This is purely estimation).

      The data is rated at 24V, which is a 6S LiPo battery voltage. For 20 mins of flight time, you will need about 6000mah, but of course the bigger battery you get, the heavier it gets as well, so you need to adjust your quadcopter’s weight in the calculation above.

      So a 6S 6000mah would be a good starting point? if you can reduce the weight, you should be able to get 20mins of flight time with 5000mah according to this estimation.

      Reply
  29. Krishna

    Hi I’m a beginner in making this quadcopter. So need some help… I m using EMAX CF2822 1200KV
    And total weight would be around 1.7kg. So what ESC and what battery should I use? I need to perform acrobatics. And how many such batteries should I use

    Reply
    1. Oscar Post author

      Well, i can’t find any data regarding this motor, and I have not personally used it, so I can’t recommend a setup for you.
      maybe check with the seller where you buy it from.

      Reply
  30. Jacek

    assumptions are good but at some point battery weight will be too much and your multicopter will not liftoff even if your calculations will predict 20 minutes of flight time with huge battery, so you should accommodate for maximum battery weight.
    As rule or thumb we always set maximum payload of multicopter so it can lift itself at 45% – 50% of throttle.

    another problem is with battery performance you set that 25c – 50c batteries are ok . From experience I can tell that cells in each batteries are not equal and some discharge quicker and some discharge slower, for light multicopters you can get away with small C battery rating but for heavier hexa or octo copters you need 65C – 135C or pair of batteries connected in parallel to minimize discharge impact on each cell.

    Reply
    1. Oscar

      Thanks for the input! :-D
      About batteries that are too heavy to lift, that’s why I conducted a series of load tests first, to find out what the max weight it can lift (well, I would consider 80-85% throttle Max, so still have room when voltage drops), then select batteries that weights below that.

      Reply

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