I need to make a compact drone that does not need to be fast, nor very power efficient*. I wanted to know what is the most mass I can lift with the smallest footprint**.

To make this question more answerable: which is more compact for the same amount of payload (say 50g), a helicopter, a quadcopter, a quadcopter with duct-fans, or another strange configuration like: the dronut, the rollocopter or the ball drone?

Are there any resources out there that have made such comparisons?

* Not exactly true.

** Footprint - in case it was not completely obvious what I meant - is the transversal area of the drone. Or consider it a volume and assign it the volume of the smallest sphere that can contain the whole drone while flying.

  • $\begingroup$ As it stands, this question is rather broad: do you have any requirements for things like flight time or engine types (a cluster of rocket engines, for example, can generate impressive amounts of lift for a few seconds)? Do you need to be able to hover (hovering requires more power than forward flight)? $\endgroup$ – Mark Apr 14 '20 at 23:43
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    $\begingroup$ I would also add - how much would one be willing to trade off for reliability? Would someone rather lift the best quality camera, for example, but the loss of one prop destroys the quad and the camera, or would it be preferable to lift a lighter camera on a hex, but have the added insurance that a single motor failure is recoverable. $\endgroup$ – Drones and Whatnot Apr 14 '20 at 23:48
  • $\begingroup$ fair points. I probably need to rephrase this, or ask a bunch of different questions. How would I even accept an answer as correct? $\endgroup$ – user27221 Apr 14 '20 at 23:59
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    $\begingroup$ I think probably this is too complex/specific to answer here on SE. I would suggest a direct conversation with an expert in the area on the details of your project. I would be glad to help out, and I have some ideas, but I would need to know a lot more about what you're trying to accomplish. Feel free to get in touch. $\endgroup$ – QuadMcFly Apr 17 '20 at 13:44
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    $\begingroup$ @QuadMcFly, as it stands, it looks answerable to me: "given this payload, which fan configuration provides the smallest footprint?" $\endgroup$ – Mark Apr 17 '20 at 20:22

Assuming you can only use up to four motors (because if you used six, eight, or even more you could just lift something with brute force) the most thrust dense configuration would probably be a ducted fan quadcopter.

The reason for that is ducted fans essentially stop a lot of air from being propelled sideways and more air goes down. Ducted fans can provide more lift and are more efficient than open-prop designs.

A helicopter would only have one motor and would need to be much larger to provide the same thrust as a quadcopter. Those other configurations mentioned would also not have nearly the thrust of a quadcopter of a similar size.

So, the best option would be a ducted-fan quadcopter (or hexacopter/octocopter if you can use lots of motors) with oversized motors. A good propeller would be a large prop as it gives more thrust at the expense of maneuverability and acceleration. Wider motors give you more torque but taller motors give you more RPMs so that depends on the prop. (A heavy aggressive prop should go with a wide motor and a lighter prop should be paired with a taller motor)

If you don't really care about longevity, get a powerful ESC, high cell-count battery (probably 6s), and get a motor that is higher than normal KV for maximum thrust and power at the expense of the motor's longevity. But be careful to not go too crazy with the high KV as it could potentially burn out an ESC or destroy the motor.

Also, as durability is not really that important for the purpose of this specific build, make it as light as physically possible (but still rigid, you don't want vibrations or flex) so that it can lift as much weight as possible.

Hopefully, this helps, as I'm not really sure what all of the requirements of this drone are.

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    $\begingroup$ Worth mentioning a co-axial octocopter configuration. Essentially a second set of motors underneath the first set. $\endgroup$ – QuadMcFly Apr 21 '20 at 11:32
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    $\begingroup$ But is putting 6 motors instead of 1 better? Isn't it the transversal area all that matters? As I understand more motors would only improve manoeuvrability, wouldn't it? $\endgroup$ – user27221 Apr 22 '20 at 10:38
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    $\begingroup$ @QuadMcFly is there any point in co-axial? I thought that at some point the prop just stalls and you can't push any more air through that area. Co-axial would be similar to a tall motor (no clue, asking here)? $\endgroup$ – user27221 Apr 22 '20 at 10:40
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    $\begingroup$ It's still more thrust than a quad configuration even if it's not equal to double the thrust. So whatever motor you choose, if you add 4 more of them you're going to gain quite a bit more. For heavy lift it's pretty useful. I believe the heavy lift multi-rotor that was hauling that YouTuber around was a co-axial octocopter. $\endgroup$ – QuadMcFly Apr 22 '20 at 11:36

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