SWIFT Propolsion unit 1st test


SWIFT Propolsion Unit


To make the system as light as possible and to eliminate the wire weight we made Swift`s propolsion unit in a small volume , components are colse to eachother .We used High density Li-ion round battery and all batteries installed inside carbon tube and electronic unit located behind the motor and this units is also a motor mount. To get the high performance from propolsion unit, we customize the engine, and we gaves spinner shape to the rotator of engine.for more information and Photohttp://www.danishaviationsystems.dk/news/2015/swift-part-ii/#prettyPhoto

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  • Damn!  Just started working on this very concept recently (18650 Li-ion batteries, in series, in a hollow tube like a flashlight body, which doubles as part of the structure - arm and/or (strong) landing gear).

    I think it was Forrest Frantz's post a while back on the higher energy density of the Li-ion 18650 cylinders in his 'world endurance record' machine that got me started.

    Such an obvious and elegant 'next step', I should have guessed lots of people were ahead of me :)

    I can still see several twists for paralleling the Li-ion batteries to chip away at the low-C problem (all the way up to 4S4P if you wanted to go there).

    I can hardly keep up these days.


  • Hi Julien, Ive got a H copter design with only 2 motor support spars going completely side to side,

    it might be possible to stack the batteries end to end in each one. using a thin carrier to 2S-2P them and combine them for a total of 2S-4P.

    I don't see a balancing problem and at the lower current outputs you expect of a Lithium battery and higher efficiencies I don't see a heating problem if kept within their C rating either.

    I have already designed one that could easily hover within the 18650PD or PF battery continuous C rating and be usable up to 90% power or so before exceeding the peak ratings.

    And since it hovers at about 35% throttle he need for 90% power is very limited and could easily be current limited out.

    The trick with Lithium batteries is to design the entire copter for a low C hover - minimum weight - maximum efficiency.

    The significant considerations are the most efficient motors and the biggest diameter props you can use on the copter size you are making and keeping everything light.

    Currently planning on 8 - 2900mah 18650 PDs/PFs in a 2S-4P format (they have a 3.4 C rating) and am definitely planning on placing them in the 2 motor support spar tubes.

    Eight inch props on a sub 2 pound quad with KDE 2206 motors.

    Verified on Xcopter Calc.



  • Great stuff. Always nice to see some innovations.


    About the heat issue. True but a few openings along the center of the arm can alleviate that. Maximum stress is typically at the end of the arm (motor side opposite) so openings not too far from the center can be made with no adverse effects to structural integrity.

    About moment of inertia increased. That  increased moment of inertia   actually helps with hovering stability when only minute adjustments are required, so doubtful it would have negative consequences in real life. Sure recovering from hard rolls and pitches  would indeed require more power, but plain hovering or mild horizontal moves may actually benefit from this and require similar or less power.

  • Interesting and compact design, just some thoughts:

    - the battery and ESC inside the tube will heat more, that could be an issue

    - the arm with the battery opening will be weaker

    - need to replace several batteries for example if used this concept for a multicopter

    - in the same multicopter case, you'll have the masses farther from the rotation center that will increase the moment of inertia and then the required forces to maintain attitude... so more power consumption.

    - still in a multicopter use, you would have to ensure all batteries will be consumed the same way otherwise, and that's almost impossible so there will be unbalances that will make the FC job much harder.

    So, your design is very interesting but definitelly not  suitable for multicopter imo.

  • Very nice design!  Love it, as a disciple of Colin Chapman.  Every component should have two functions.

  • Really nice modular propulsion unit and great use of CF tube to hold 3 18650 in series.

    Seems like it could be a useful concept in a quadcopter if you could keep the current low enough.

    Best Regards,


  • Hi,

    we are testing different kind of batteries we got best result with 18650 , of course you should consider the C rate, but if you are using on small airplanes it is definitely perfect choice.  we will publish the results soon.

  • Great work! Do you have any thoughts on the reliability of the 18650 cells-in-a-tube concept? I have some Samsung INR-18650-25R cells that I'm trying to work into a propulsion unit. This looks like a really slick approach. 

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