drone in the sky

Not just another drone project

Powertrain & flight time

Compared to racing drones we do not aim for high speed and acceleration values. A camera drone needs as much flight time as possible while still being able to get the job done. All other characteristics like range, quality, speed just need to be as good as necessary. This assumption allows us to reduce the complexity of the problem a little. It leaves us with an optimization problem where we want to have the max. flight time while keeping all other components “just good enough”. The definition of “just good enough” is different for every project. Sometimes it is necessary to adjust your definition slightly in order to get better system performance.

With this project, my aim is to get a flight time of somewhere in between 22min and 30min. This drone will be very similar to a DJI Phantom, so Phantom components are a really good starting point.

Motors & Battery

We choose the T-Motor 6th Anniversary MN2213. All four of these cost around 70€ (which is really cheap!). Looking at the specs they are a perfect choice for our project (if we wanted to spend more money there might be better alternatives):

They produce around 600g to 700g of thrust each, running on 3S with the included 9″ propellers. So the current draw is somewhere around 3A while hovering. Tests by other users show that they can easily handle a bigger propeller (~10″). That will increase the efficiency and will give us a hover current of around 2.5A running at 3S.

Using a 4S battery would give us a lot more thrust but efficiency will be lower thus flight time will decrease. This is not something we want, but worth to keep in mind in case we want to have a heavier payload someday.

At this point, we do not know the exact numbers since we just use thrust data gathered by people of the internet. A 3S 5200mAh LiPo (similar to what’s inside the Phantom) will most likely give us the flight time we want.

It took a lot of iterations till I found a good motor, propeller and battery combination. Looking at existing builds or commercial products specs definitely help and speeds up the process. Especially the pre-estimated weights of the battery and overall UAV really help.

Sometimes it can be hard to find proper motor thrust/power consumption data. It is not worth looking at motors that do not come with detailed thrust stand data.

ESCs

Just pick whatever gets the job done. I choose 20A Bel-Heli ESCs. All in one or not does not really matter.

6 thoughts on “Not just another drone project”

  1. Laurent says:

    Hello,
    I follow you for several months in your project DroneBridge having also long wanted to build a drone dedicated to the photo / video.
    To follow you on this project I ordered the following elements to build my drone.
    – Turnigy i6S radio with smartphone / tablet support.
    – Omnibus F4 Pro flight controller with barometric sensor
    – Ublox N8M GPS with Compass
    – Four 2312 980 Kv engines with 9450 propellers
    – Four controllers 30 A
    – Chassis S500 from Hobbyking
    – GoPro STORM32 gimbal
    – Two Raspberry Pi 3 B
    – Two ALFA AWUS036NHA (AR9271)

    What will you advise me as batteries? 3S? 4S? 5000 mAh / h?

    I did ground tests on flat ground of the DroneBridge link and the resiltat is of the order of 610 meters for the moment with the antennas Omni 3 db.
    When the drone will be in flight condition I could do the test ground / Air which should logically be much better. It should be tested with a circular polarization antenna side drone and a directional antenna ground. (and why not an antenna with motorized tracking in the future …)

    I keep you informed of my tests.

    Laurent

    1. cyber says:

      Cool project! Sadly I never really tested the range. Always kept on developing and trusting the guys from wifibroadcast that they are right with their numbers. But in air should def. improve range a lot! New tests from WifiBroadcast (low transmission bit rates I guess) show up to 7km of range!

      Do you have any data about power consumption of the motor-propeller combination? Google might find some user tests. Like how much amperes one motor draws runing on 3S/4S while providing 300g of lift etc.
      With that data and your overall weight of the drone you can sort of estimate what battery would perform best in your case.
      – Lets say your drone is 1300g -> 325g/motor to keep it in hover
      – Look up the amps or watts drawn at that load on 3S and see how long a 5200mAh 3S would last etc.

      From my experience I would say you are right to go for 5000+mAh. 3S batteries are lighter and give a bit more flight time in my case (at least on paper – did no tests with 4S). So maybe 3S is for you also.

  2. Laurent says:

    In fact I took the same technical specifications as the DJI Phantom 4 for engines and propellers. The Phantom 4 is also powered by a battery in 4S it seems to me.
    For the DroneBridge side, does lowering the Wifibroadcast transfer rate to increase the range affect the DroneBridge protocol such as latency at the RC level or telemetry?

    Best regards

    Laurent

    1. cyber says:

      If it is the same motors that DJI uses then 4S is the go to (as you said DJI uses 4S as well).
      The problem is that every motor type is different. KV and stuff does not allow to compare motors on matters of efficiency. Size, quality and number of magnets, diameters, spaces in between the parts, prop diameter, prop angle etc. determine the efficiency. But I’d say that you can’t be wrong by choosing any of the battery types (3S, 4S).

      DroneBridge RC, telemetry and status messages take up very little bandwidth compared to the video feed. So lowering the transmission rate should not affect any latency etc. It might become critical on the lowest bit rate settings. But I have not tested that.

  3. Marcus says:

    Great project, thanks for keeping us up to date!
    I actually wanted to post this on DroneBridge but the comments there seem to be closed.
    Looking at the hardware diagram I had a question: Wouldn’t the Raspberry Pi easily be capable of providing at least the same funcionality as the ESP32? In other words, allow for direct connection of an Android phone without an additional ground station? I am of course talking about a Raspberry Pi with Wifi.

    1. cyber says:

      Hi! thanks 🙂 I closed comments because of a vast amount of spammers.

      Yes, that would be possible. The advantage over the ESP would be that we can also send the video stream. I guess we could also have a higher range in case we hook up a high power WiFi card to the AirPi.
      In fact, that was the first working setup I had. Just a pure WiFi connection. I ditched it because of the advantages that come with WiFi adapters operating in monitor mode.
      The current implementation still contains some code from that time. All modules have a command line argument called “-m (mode)” that can be set to “w” for WiFi, however, it is not implemented at this point.
      At the moment I have no time to add it, but I think it would be a nice thing to have in the future.

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