Some MultiCopter Design Thoughts.


Hi All, Just pulled this image in from SUAS News (Thank you Gary) to illustrate a few really good concepts that it incorporates and talk about better Multicopter design a bit.

This copter has a lot of things right and is really a study in design excellence.

1. Most obvious is a sliding ball full enclosure camera Gimbal, very pro and really something we should be striving for.

2. The motors are on the bottom under the arms: More aerodynamically efficient with no prop wash interference and very little intake interference. Noticeably increased flight times and greater lift capability and much quieter.

3. Large slow high efficiency props and pancake motors: These are way more efficient than faster motors with smaller diameter more conventional props.

4. Carbon fiber aerodynamic frame arms: Again more aerodynamically efficient, light and strong.

5. Fully enclosed framework and a simple spring loaded landing gear that provides as little interference with the prop wash as possible.

Basically this quad incorporates the best design features I have seen so far and definitely provides food for thought.

I thought it might be worth soliciting comments and other thoughts about optimal multicopter design techniques.

Best Regards,


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  • I spent a lot of time experimenting with intake bellmouth designs which worked well on the test rig but did not do anything for the flight endurance in reality. The weight of the light foam board was enough to offset any gain in lift efficiency. It also had a neg. effect on stability. Another effect was that it requires a significant gap between the blade tips and the venturi as the tip losses go up dramatically. Opposite of what you would expect but this is not a compressor...

  • @Denny "The more motors you have the less efficient it is". That's not entirely true.

    See Andrew's comment, "Then there are ducted fans (EDF) most all of which have the hardware on the intake side...could that be wrong? "

    More ducts=more efficiency.

    Air intake is super important and shouldn't be underestimated :-)

  • :)Denny Rowland , Im doing a similar thing now in Uganda, but bird nests are in trees and is only a small percentage of my work. Doing it for fun was great but when it becomes a job and doing it day after dreary day, it makes you want to just get a foamy and get back to basics again. Shouldn't complain tho, I do consider myself blessed and should be more thankful:) Thanks to Chris and the 3DR team that got me going on the APMV1.0 all those years ago!

  • Choppy

    I had an interesting assignment last year which was to photograph hundreds of Vulture nests on the side of some vertical cliff faces that led down to the sea. I had to fly within 3 feet of the nests so that the eggs could be counted which demonstrated the effect you are talking about the closer you get, the greater the Bernoulli effect drawing you in closer and closer. I was operating from a small rib in the sea so that I could view from below and judge my distance. It was a very tough job.....

  • @Andrew Rabbit, Thats where I was partly getting my conclusions from, ducted fan theory/ white man magic. Any impediment or intake reduction can reduce airflow thus need more power for the same amount if thrust.

    The other area is from doing a helicopter CPL course and I remember when I wasnt sleeping or staring out the window something about Vortex Ring State and how walls or anything close to the tips of the rotor blades can induce more VRS  and give the sensation you are being dragged into the wall . Just maybe when I get home to OZ, I'll do a test on long and short arms?.....Too many projects.....

  • @Denny

    LOL, I really like that term "persistent stare capability" but it might frighten Diane and the Deer Park folks...

  • @Andrew Rabbit

    That's an interesting speculation about the turbulence/drag sensitivity of the "intake" side of the prop. So perhaps there is a high sensitivity to the particular geometry, spacing, sizes etc.of a particular multi that is much more a factor in a down-facing setup? That might explain results that contradict theory as well as each other. Also wonder what effect flying around has, as opposed to hovering, as the intake side of top-mounted props would have more turbulence when moving. Then there are ducted fans (EDF) most all of which have the hardware on the intake side...could that be wrong?   

  • As I mentioned on Aerobot's FB page, Simon's test might be showing a decrease in efficiency due to a change in COG, as a result of flipping the motors.  A higher COG will make the copter work harder to maintain level flight, thus using more power.

  • With the use of a tri-copter and Panasonic NCR18650B or the GEB8043125 batteries. An endurance of well over two hours can be expected. The Tri-Copter has a vane steering system so no rear motor steering is required.

    The more motors you have the less efficient it is. 

    The endurance model forms the basis for a cameraship with APM2.6 and the new style gimbal. It will have persistent stare capability for at least an hour. With a locked in pointing accuracy of .005 deg.

  • Hi All, with Simons test showing negative results, could it be possible that the induced airflow above the prop disc has been impeded by the center section airflow being turbulent? Maybe the arms can be longer to eliminate any chance the body is producing less than ideal conditions for the entire disc area to receive vertical airflow from above?

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