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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  • 3692931241?profile=originalThis company explain a lot why having reverted props is better...also some new design..

    it is not cheap but for sure is not 50K

  • Developer

    Doug, the observation about sound is very important. And easier to test for with practical applications. 

    With everything else being equal, a silent copter is the more efficient system.

  • Yesterday I read the entire RC Groups thread regarding the bench tester and tests run by OMM and Rusty (had dinner with Rusty and two other colleagues about 4 weeks ago in ATL), 30 pages. Their work was focused on motor thrust - current - rpm data. The data is still available at OMM's ftp site. That work was in 2009. The arm of their test rigs were round.

    The earlier mentioned post by Rusty touched on the prop-arm distance and the resulting 'compression vibration' (my term) that the impinged air mass makes on the arm. If I remember correctly his flight results of over/under arm were inconclusive -- dead even, essentially. The sound level on the other hand was significantly lower.

    Where there is sound, there is energy...


  • There are much better Brushless motors coming FWIW which will improve the current situation with the conventional outer axis gimbals. I would imagine that they will have overlapping magnets to improve the linearity and a hollow shaft. 

  • Andrew That is worth knowing as my coils are home made and are an integral part of the model. I like most people I expect, I have a few dead hard drives laying about.

  • Voice coil actuators are used in hard drives to control the read-write head.  Now there's a source for some inexpensive hardware to play about with... ;)

  • I cant say how ecstatic I am about Jason Shorts Drift mode which I have yet to try. This will bring a new dimension to the way my system will work.

  • I forgot to mention that a typical inner axis stabilizer only moves about 2.5 degrees in all three axis. In my case it is 5 degrees. If you study the degree of disturbance from a good MR that has a fixed camera it is remarkable that the typical disturbance is rarely more than 1 degree which looks awful.  

  • Having shown the reasons why a tri-copter is the most efficient lifter (and it flys nice too) We come to the camera stabilization. As weight is the enemy I cant see any good reason for duplicating the roll pitch and yaw functions that the model provides us with. so what we need is just the tilt function so that we can fly the camera single handedly and the model follow that track. The Phantom Vision is a nice simple example of how that works but it lacks stability. This is where the clever bit comes in. By making a sandwich plate that sits between the camera assy and the model we can stabilize that platform to an accuracy of .005 deg. this is about the same as a cineflex which is arguably the worlds best full size system. So how is this done? It is easier than you may think. Your Brushless gimbal struggles to maintain even .5 deg. accuracy because it has weak torque hold and importantly it is not a linear motor. You can however control another type of motor called the Voice Coil Actuator and you can do it with a normal brushless controller using two of the pins. The VCA is what you will find in every inner axis mil spec. gimbal and it is so fast it can attenuate most of the vibration frequencies that the model can produce. It does exist and I have it working as you will soon see. I would from a personal point of view say that this has to be regarded as a major step in the right direction.

  • Hi, interested to know on how do you test the prop/thrust efficiency, is there any software for it? I'm interested to test mine as well.TQ

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