Coaxial Cinestar...

Discussion in 'Cinestar Misc' started by Benjamin Rowland, Jan 26, 2013.

  1. Todd Livdahl

    Todd Livdahl New Member

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    Did you get the A2 built up and what differences are you seeing if any?
     
  2. Sam Fleishman

    Sam Fleishman Member

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  3. Dejan Mugosa

    Dejan Mugosa Member

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    Well guys this is mixer, motor and prop settings.
    So just by changing numbers would need a lot off testing. And I do not recommend it with stock DJI mixer.
    A2 also has some problems with bottom motors on stock setting and don't ask me why but the real power is not avalible while wkm does not have this problem.

    Test test and teas just watch it that it does not spin beyond control.
     
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  4. Sam Fleishman

    Sam Fleishman Member

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    What is kopterworx suggested motor mix for wookong to get the least efficiency loss and even temps on top and bottom?
     
  5. Dejan Mugosa

    Dejan Mugosa Member

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    There is no quick mix. Each motors on diferent props are different. And so it is more testing and bench tests to get the amps and trust the same. Othervise the MK mixer with 1 inch diference on bottom top is nice for wkm.
     
  6. Tristan Twisselman

    Tristan Twisselman Active Member

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    So I have been thinking lately. Would the props overlapping a few inches rather than being on top of one another affect stability in a negative way? What if instead of a coax with 4 booms, you kept the 8 booms and just put every other motor upside down. Still a flat octo but can run props as if it where a coax. I have never tried this but was curious if anyone else has.
     
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  7. Steve Maller

    Steve Maller UAV Grief Counselor

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    I have been wondering about that for a while. I don't think the motor mixing would be affected necessarily. But there seems to be evidence that the coax design has some stability advantages. Among other things, the flat mixer I think only utilizes 4 of the motors for some of the directional operations on a flat copter, whereas all 8 are utilized in a coax. Could be why they're more stable. But the flat design definitely can stay aloft for longer, so there could be advantages.
     
  8. Tristan Twisselman

    Tristan Twisselman Active Member

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    Same here Steve. I am thinking about setting up one of my coax as described with flat octo but still running 18'' props and see how it flies and how things are affected; such as flight time and stability.
     
  9. Ozkan Erden

    Ozkan Erden Distributor

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    I have been doing this on my flat octo for a while. The props are overlapped each other by only one inch, as far as I can say, the stability is not affected. And actually, the motors are not upside down. I raised 4 of the motors just an inch to have enough clearance for the props.

    When you mount the motor and prop upside down, you will catch the prop in the camera frame a lot when flying straight.

    Because of the efficiency loss on X8 setup, I don't use it. I get almost %20 more flight time with my flat octo with exactly the same setup. (I had to build an X8 with 5215XF-435KV though :) )
     
  10. Jason Smoker

    Jason Smoker Active Member

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    Ozkan can you post a pic of your set-up please? I want to see this overlap
     
  11. Ozkan Erden

    Ozkan Erden Distributor

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    Sure, you can see it attached. The tips of the props cross over each other just an inch.

    The height difference between props are just a little bit more than an inch.

    IMAG0598.jpg
     
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  12. Steve Maller

    Steve Maller UAV Grief Counselor

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    That's pretty nifty. But I don't see any landing gear. Do you have somebody grab it from the air when you land? Or are you good enough to land it back on those tripods? :eek:
     
  13. Ozkan Erden

    Ozkan Erden Distributor

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    Yes Steve, we take off from tripods but camera operator catches it on the air when landing. Since it's flat octo, it is safe. For coaxial setups, this would be scary.
     
  14. Tristan Twisselman

    Tristan Twisselman Active Member

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    That is very interesting. Thanks for sharing the photo Ozkan. So no weird flight characteristics, but allows bigger props like a coax would yet you still get the longer flight times of a flat octo without the efficiency loss?
     
  15. Ozkan Erden

    Ozkan Erden Distributor

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    No weird flight characteristics. Since my overlapping area is very small, I don't think it effects the flight time at all.

    I recommend this topic for overlapping prop design:

    http://www.multirotorforums.com/showthread.php?5870-Overlapping-Propeller-Designs

    And also this video is very helpful with bench tests:



    In this test, the props are overlapped almost %50 percent.
     
  16. Jason Smoker

    Jason Smoker Active Member

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    Thanks for the pic! :)

    Is that a 500mm cinestar frame are you running 16inch props instead of the 15?

    does it sound any different flying with that set-up?
     
  17. Mark Harris

    Mark Harris Member

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    I'd be worried about tip vorticies interacting with each other on slightly overlapping props - you could be inducing quite a lot of vibration into your setup.
     
  18. Jason Smoker

    Jason Smoker Active Member

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    I also be worried about the prop flexing and hitting the other prop when its windy
     
  19. Ozkan Erden

    Ozkan Erden Distributor

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    Before going with overlapping setup I checked both topic for sure: Vibrations and prop flexing. Even the prop flexes at the maximum level, it doesn't touch the other prop; there is enough space. Vibrations: I couldn't measure any difference for my setup.

    The booms are 550mm and the props are 18". After sending those motors to KDE for upgrade, I installed new set without overlapping. I had to use Tarot's motor mount to fit the 18" props with 550mm booms. 2 cm in the total diameter makes a huge difference, I can't fit it to my station wagon with the prop installed now.
     
  20. Dejan Mugosa

    Dejan Mugosa Member

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    HAHAHA like our coax pictures.

    Well we had an expert do the math and test for us and there are many factors included in this test that you did not take account into.
    Like motor rpm, props size and agle .....
    So average coax loss is about 12 to 15% while it can less or like you figured out also more. Also depends on what trust ratio you are trying to get. If you stick to 50% off the total motor trust you will get less loss than at 70 ot 80%.

    But I would realy like to see you fly with 18 inch props with ockto and travel around the country with it. IT will be a huge problem and pain in the a....

    Overlaping at the end makes it the same as coax most off the time. That is why you takle that extra 20% stronger motors and you don't care about the trust loss.
    While the performance of coax is better than ockto, specialy in wind and similar conditions.
     
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