Get Longer Flight Time on Multicopter

It’s hard to determine flight time on a quadcopter without actually test it, because it depends on many factors: average flying speed, battery, motor/propeller efficiency, payload, wind speed etc. However there are ways you can do to maximize your flight time in the air.

There are differences between “flight time” and “hover time”. Hover time is pretty much a constant value, but flight time varies depends on throttle level and wind condition. Therefore you can’t really compare the “flight time” between 2 different multicopters, it’s not fair as it’s influenced by so many factors.

large_Quad_Copter_01

Generally speaking, low KV motors with large propellers have higher efficiency and can carry larger battery, and thus longer flight time.
But you don’t have to build a gigantic quadcopter to stay longer in the air. In this post we will discuss what impacts battery life, and some of the things you can do to maximize your hover time as well as flight time.

Throttle and Power Efficiency

Brushless motors and propellers tend to have the worst efficiency at maximum throttle, and higher efficiency at lower throttle.
Therefore flying around fast, doing acrobatics etc, will use more power thus shorter flight time. If you are doing aerial filming, and want some more time in the air, the best thing to do is to fly gently and avoid unnecessary turns.

Weight – Payload

As you can probably guess, the simplest and most effective way of increasing your drone’s flight time, would be to get rid of unnecessary weight. Every gram you shave contributes in extra flight time.

Here are a few suggestions for keeping your quad as light as possible:

  • make motor/ESC/power wires as short as possible
  • avoid gold bullet connectors and just direct solder
  • remove HD camera (GoPro/Mobius) when you are not recording
  • use light weight components and hardware

Battery

Capacity

Battery capacity directly affects flight time. Bigger battery doesn’t necessary give you longer flight time, because battery weight increases with capacity. There is a trade off (balance) between capacity and flight time.

flight-time-vs-battery-capacity1

Check out this post about how I choose the optimal battery capacity.

You can experiment with different sizes batteries, time it and find out which one gives the best result.

C-Rating

LiPo Battery C rating not only affects the max continuous current draw, but also flight time in my opinion.

lipo-battery-c-rating-affect-flight-time

How? Let’s assume, you use up 80% of the battery capacity when the voltage drops to 3.5V per cell. If you have a low C rating LiPo battery, and your multicopter demands more current than the battery can handle, you will notice your battery voltage will start dropping very quickly. In the end, you might only have used 70% of the total capacity when the voltage sags to 3.5V per cell (and recovers to 3.8V after landing). This is a symptom of insufficient C rating, and you will have shorter flight time.

Battery Condition and Maintenance

This could well be a whole new topic, and there is simply too much to cover. But basically, your batteries will get old and the capacity they hold will start diminishing. It’s important that you keep them in good condition, avoid over-discharging them, and do not leave them fully charged for too long. Here is a guide on how to use and look after LiPo batteries.

Motor and Propellers

If flight time is more important than power for you, then by choosing an efficient motor and prop combination will help immensely. You can find out motor efficiency information from the data sheet, or thrust tests done by other hobbyists.

diy-simple-motor-thrust-measuring-stand-test-station-simple-example-1

Motor, propeller efficiency is calculated by dividing thrust by power, which is gram per watt (g/W). The higher g/W, the more thrust is generated at a given amount of energy. For example when I am using the Cobra 2204 1960KV motors, 6045 propepller gives me a lot of power, but I will get longest flight time by using 5030 props because of the higher efficiency.

Here is a guide on how to choose mini quad motors, and propellers.

Also balancing your propellers could increase your flight time too. Unbalanced propellers introduce vibration to your aircraft, not only the aircraft woulfd use more energy trying to stabilize it, energy is also wasted on friction between propeller and air.

Flight Mode

Although not a very big deal, but flight mode does affect flight time too! Here I mainly refer to Rate mode (AKA manual mode or acro mode) and Self-Level mode (AKA Angle/Horizon mode). To find out the difference, check out this post.

Self-level mode is fantastic, because it helps your control by attempting to keep the quadcopter level. However as it’s constantly trying to fight with changes of craft attitude, the motors speed are changing more rapidly too and use more energy.

Rate mode doesn’t correct the change of attitude as hard as self-level mode, so in theory it’s more power efficient.

PID tuning!

Just like what we have mentioned above, aircraft with vibration could cause overheat motors and use more energy. A well tuned, smooth, and stable multicopter is more efficient and gives you longer flight time.

Wind

Wind causes instability to the quadcopter, and the motors have to work harder to correct the errors to stay level. This means that flying in windy weather drains battery faster than flying in a calm day.

Additional Components

Additional parts such as LED, FPV gear, camera gimbals etc can reduce your flight time. Firstly they draws current although not a lot. Secondly they are extra weight to your quadcopter.

Each LED used on multicopters generally only draw 20mA to 30mA of current, so at 5V, the power consumption is only about 0.1W each LED. Say if you have 10 LEDs  that’s 1W in total.

Emax-nighthawk-250-mini-quad-added-WS2812B-led-strip-underneath

Your FPV gear could draw up to 0.5A at 12V for example, which is about 6W.

Now assume you have a mini quad, at hover 1 single motor draws 15A at 16V – 4S (pretty normal for a mini quad at forward flight), which is 240W, and 960W in total for 4 motors.

LED and FPV gear combined is less than 1% of the total power usage. Put that in flight time terms, if your flight time is about 5 mins (300 seconds), that’s only 3 seconds that you lost.

But the weight of the hardware would have a much bigger impact on flight time.

9 thoughts on “Get Longer Flight Time on Multicopter

  1. Ole

    Hi Oscar

    I got a question choosing prop.

    I am choosing between 3 props. Will the prop that gives the most thrust give the shortest flight time?

    Reply
    1. Oscar Post author

      flight time depends on prop/motor efficiency, also depends on how much throttle you apply during the flighyt…
      Thrust is only part of the equation…

      Reply
  2. ZetEm

    Hi Oscar,
    yes, your LEDs and gear consumpt very low % of your battery, but you haven’t forgotten they increase weight of your copter

    Reply
  3. Will and Tracy

    Hi Oscar!
    Long time reader of your excellent articles and tips, I am very grateful for what you do, so let me start with a humble Thank You. I’ve been curious about this topic myself for quite a while, to the point where I was performing hover tests and calculating results. While I don’t have the means to afford a motor test stand, I am blessed to have two almost identical ZMR250’s from Sitela, (you think that Cytryna PDB was complicated, look at the Sitela!), with which I have configured with different motors typical of the class (1806s from RTFQ on mine, and 2204s from EMAX on my fiancées). I thought that configured this way, with almost everything else being even, I could have a reliable gauge as to battery life.
    I was incorrect, and still at a loss as to which setup is more efficient. We’re both running 5030s, 1400mah 40C 3S, 15A BLHeli motors, and Flip32+’s. 6 minutes is where our timers are set, and it seems we always return with 11.3V on both ZMR’s. Once I get a better gauge on their flight times, I can be a little more liberal with our timers.
    Is there a general rule of thumb for the 250 class regarding 1806’s vs 2204’s? Or 5″ vs 6″ on 3S? I know your article was full of science, and here I am asking for generalities, but I thank you for your answer either way.

    Reply
    1. Oscar Post author

      not really… efficiency really comes down to the motors and prop for mini quad… even the same size motor from different manufacturers would give you very different characteristics.
      but anyway, i generally find mini quad motors around 2300KV, runs most efficiently with 5030/6030 props on 4S, with 3S, i think 6030 is probably better… but you need to test it really to confirm.

      Reply
  4. Bradley

    Hi Oscar,

    Just FYI BlHeli ‘Dampened Light’ is actually regenerative braking (ie uses the motor as a flywheel generator and sends the power back to the battery) meaning it actually recovers a small amount of energy when slowing the motor rather than just bleeding the power off through the FET’s like regular ESC braking does.

    So theoretically enabling Dampened Light should actually slightly increase flight times especially when flying like Chad Nowak :)

    Brad

    Reply
  5. eephyne

    Very nice article as always. Really helping to figure out some elements to lighten the multi.

    Thanks Oscar

    Reply

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