Will it work ... ??

Discussion in 'Cinestar Misc' started by Sebastian Meredith, Oct 16, 2013.

  1. Sebastian Meredith

    Sebastian Meredith Active Member

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    I had a random thought after an very interesting response to a thread I posted here. Shaun Stanton was passing on some useful info on "Vortex Ring States" and related issues and mentioned the influences on Flat 8s and Coaxial setups. Which as I mentioned further in the post an corroborated by Steve Maller had lead to some head scratching thoughts ...

    So here goes one of my head scratching thoughts ...

    As I understand it, converting from a Flat 8 to a Coaxial setup increases the stability of a unit during flight especially during descents compared to the Flat 8 ... one of the reasons being the elimination of the spoon effect caused by the surface area created by the tip to tip props.

    So I pose this scenario ... What would happen is you kept the 8 booms and every alternate motor on a flat setup, you rotated 180 degrees to face down, then making sure the prop and motor spins i the correct direction. Now you have a displacement of the props breaking the spoon effect somewhat.

    Will this work?
    How would this handle? could it be an in-between solution between an flat 8 and a coaxial setup?

    Just a random thought to see what others think? :rolleyes:
     
  2. Tyler Olson

    Tyler Olson Member

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    Would it work? yes.
    The distributor here had tried it for a customer to test it out and the flight times were longer because he was able to use larger props but I'm not sure what other reasons for or against he had. But I do know it can be (and probably is) being done.
     
  3. Sebastian Meredith

    Sebastian Meredith Active Member

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    Tyler, would be great to get some feedback from the distributor on this. Got contact details for them?
    Would be interesting to see if the stability in windy conditions were improved.
     
  4. Shaun Stanton

    Shaun Stanton Active Member

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    I suppose a con is that you still have a larger footprint of the Flat 8 and. That's another advantage to the coax I am about venture into this thing despite Steves odd anomally. I am taking for booms from my flat 8 and using in a new hub assembly and turning that into heavy lifter using a DJI WKM with FF ESC's and power distribution set. My other bird will be a medium lift coax using the same QC3328's.

    I did see an article from a company that is selling $25000 quad copters for government use that has all four motors traverse mounted. They claim that the motors being on the bottom are more efficient because there is less air being disrupted by the boom arms as the propeller blades rotate over it. I suppose there is some credence to this, because the boom arm will attenuate the slipstream a little and may even cause a turbulent flow around them and as the air pushes over it. Although this wont be the case with the Coax since one motor is on top.

    Back when I first put my CS together I had number 8 BL go out. Just for test purposes I flew the CS8 as a quadcopter once with a small Cannon Vixia, it actually handled itself well. I flew in 90 degree heat , I did start heating up the BL's but it flew for 6 minutes without issues. I plan on dong the MK coax with that fan mod to help cool the BL's

    Shaun
     
  5. Steve Maller

    Steve Maller UAV Grief Counselor

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    My issue with the failed X8 coax conversion I did was pilot error, I believe. I used my stock Cinestar parts to flip the motors over, and used the plastic boom clamps to secure the pairs of motors. I'm not sure I ever properly documented my experience here, but after exhaustive analysis, I decided that the cause of my "near death experience" was that one of the motor pairs exerted too much stress on the boom clamp, causing it to slip and the motors to rotate on the boom. Needless to say, this caused severe spinning of the copter, and nearly resulted in the loss of the copter. Remarkably (and quite luckily), I managed to get her back on the ground in one piece. The first and only flight of my X8 config is shown in part here, and no, this was not sped up. This was actual speed. The moral of this story? Test more carefully, and use aluminum boom claps. :eek:

    This video is from the GH3 that I had on the 2-axis gimbal (which, amazingly, stayed on the copter).

    Oh, and my Cinestar 8 lives on happily as a flat-8, and suffered no lasting effects. As for me, I'll miss those trousers.

     
  6. Sebastian Meredith

    Sebastian Meredith Active Member

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    Wow Steve ... that was insane ... I've just had to go change my trousers after watching that! You must have come close to cardiac arrest during that little event!

    What's your thoughts on the alternate motor setup ?

    Prop-Options.jpg
     
  7. Steve Maller

    Steve Maller UAV Grief Counselor

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    One of the main reasons going with the X8 configuration was to remove the front most boom from the camera field of view. So the up/down configuration doesn't really address that issue, and actually may make it worse by having down facing props more likely to appear in the camera's field of view.
     
  8. Shaun Stanton

    Shaun Stanton Active Member

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    Steve,

    Were you able to twist the motor mounts around the boom arms by hand? I am going to try metal on the heavy lift just to be on the safe side. In theory because both motors counter rotate you would think that their would be less rotational stress on the clamps.

    Shaun

    Shaun
     
  9. Shaun Stanton

    Shaun Stanton Active Member

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    I pondered if the copter would fly better with all 8 upside down.

    Shaun
     
  10. Chris Fox

    Chris Fox Active Member

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    G'Day Shaun,

    One other thing to consider is stability, moving the plane of the rotor disks down by 4-6" will raise the CoG higher which may reduce stability. By how much though, I'm not sure, just worth considering. This can also be counteracted though by using a heavier camera ;)

    Cheers
    Chris
     
  11. Shaun Stanton

    Shaun Stanton Active Member

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    It would raise it?? Unless I am misunderstanding what you mean by raising. Or I am looking axis perspective.

    It would seem that you would lower CG because your CG centroid of the motors would be below the boom arms. I agree 4-6 inches would be pretty not optimal. I can see some stability issues with the Center of lift being close to the CG centroid, allowing the copter to be more maneuverable on X, Y axis but decreasing its static stability when flying a light load.

    Its pretty much a mute point for me anyway I am going to do a coaxial config where the CG of the motors should in theory be in balance about the boom arm, if I am visualizing this right.

    Shaun
     
  12. Chris Fox

    Chris Fox Active Member

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    G'Day Shaun,
    It is all relative to the plane that the props spin in, so by inverting the motors, yes the mass of the motors is below the boom, however the props are below the motors, so the from an aerodynamic point of view the mass of the motors, booms, centre hub etc has all been raised relative to the "rotor disk" or plane that all the props create.
    Cheers
    Chris
     
  13. Shaun Stanton

    Shaun Stanton Active Member

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    Ok yeah I see what are saying I think I was kind of the same page just looking at it differently. That plane that you are describing would be like the Center of Lift in airplane speak exept more planar than a centroid, I am guessing. I agree that would raise CG in relation to the lift component and would make it less stable. It would seem to be negligible since a lot of these motors seem to only be a couple inches at the most. I guess if you have tall rotor housings this could be an issue.

    There is a company selling a professional product for governments like Search and rescue and police with the motors on the bottom, they seem to be getting good results with them.

    Shaun
     
  14. Juha Knaapi

    Juha Knaapi New Member

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    There is certainly some truth behind all this, quite some time ago I had also go with a non conventional frame design.
    I noticed quite a difference on wind and fast decent performance. it's slightly heavier than flat-8 because of those 4 Z-booms, but I couldn't notice any difference on flight time.

    Pic is quite old, back then I was running 2-Axis AlexMos. Otherwise, MN4014's with 16 inc prop, 6s power, WKM.
     

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  15. Shaun Stanton

    Shaun Stanton Active Member

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    Are you still using 4014s? What flight times are you getting?
     
  16. Juha Knaapi

    Juha Knaapi New Member

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    I'm still rocking 4014s on my both Octos. I can easily run 10 minute of flight times AUW being 9,5kg (Carbon Copy MöVi + FS700). I'm really conservative with my LiPo voltages, so when needed I can push the limit and get the last important shot.

    On battery side I'm using 2x 6s 8000mAh Nanotechs per flight.
     
  17. Shaun Stanton

    Shaun Stanton Active Member

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    That's awesome he'll of a lot better than the 4s setup. I am still putting my second rig together I haven't flown it yet. On the standard copter I was only getting 5 minutes on an FS-100. It was too heavy to carry dual batteries.

    Are you using the -11, 330 kv motors?
     
  18. Juha Knaapi

    Juha Knaapi New Member

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    Shaun, I'm running -9, 400kv ones (with Xoar 16x5). At the moment of first HL build they were only ones available in Europe so I stuck with them for the second one too. I really like how all electrical components on my Octos and Hexa are all interchangeable.

    I might have a second look at motor market at the launch of FF Synapse for updated optimal performance.
     

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