NEW U7 motor tmotor

Discussion in 'Cinestar 8' started by kjetil t√łnnesen, Nov 22, 2013.

  1. Shane Moore

    Shane Moore Member

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    One thing to keep in mind is that the 550mm booms can only accommodate 16 inch props. These calculations must be for X8s so you'd need to factor in a considerable efficiency loss as well. In my test it was 30%. I learned this the hard way.
     
  2. Dave King

    Dave King Well-Known Member

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    I think you can squeeze 17's on them and still get about 1/2 between props. With the 16's on the 550's I was seeing about 1 3/8 of an inch between props. I have since cut my booms down to 525mm (fitted with 16" props) so it can fit in my car.
     
  3. Shane Moore

    Shane Moore Member

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    Interesting. I have exactly one inch clearance with 16 inch props on 550 booms. I considered trimming a little off of 17 inch props, but was told not to have less than one inch clearance between the end of the props. Hopefully someone has tried smaller clearance between props and can offer some insights.
     
  4. Kari Ylitalo

    Kari Ylitalo Member

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    If you lost 30% in efficiency also something else must be wrong. In my experience lost in efficiency is no more than 5-10%, but this can be gain back increasing prop size one inch. If increasing prop size 2 inch, it's already more efficient and still flies better than flat with smaller props with dji electronics.

    Also to notice ecalc flight time estimates are usually low side, so far i've got around 10-15% more flight time in real life when flying packs to 3.4V.
     
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  5. Howard Dapp

    Howard Dapp Active Member

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    With a coaxial setup you should only lose 5-15% efficiency. The gain instability and smaller size outweigh efficiency loss. My copter is a small 35" in diameter but i'm able to mount up to 20" props.
     
  6. Tim Gould

    Tim Gould New Member

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    I recently finished a Gryphon Dynamics 1000mm X8 build and we have the KDE 4014 motors and Xoar 17x5" props mounted to it. DJI A2 and Castle Creations 75A Phoenix Lite were other components. I completed some flight testing at 28lb AUW and 33lbs AUW. This is approximate weight of airframe, Movi, 6s 20000mah and 5lb or 10lb camera. At 28lbs current draw was about 84A and at 33lbs the current draw was about 113A. This is based on battery usage. I found that at 33lbs. I was losing yaw stability when climbing because the motors were maxed out.

    Motors and ESCs were barely warm after 10min and 7min flights.

    Anyone know what gains can be made switching to T-Motor 18" props from Xoar 17"?
     
  7. Bryan Harvey

    Bryan Harvey Member

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    We have built and tested the KDE 4014XF motors on a Gryphon X8 frame with MoVI MR gimbal at 27lbs and 33lbs.

    specs:
    6S
    Castle Creations Edge Light 75A ESC's
    Xoar 17x5 props
    DJI A2 controller

    Based on KDE printed specs I was excited to test them as an alternative to the U7. But during bench testing we found the KDE motors had slightly more efficiency, but even less power than the Tmotor 4014, (similar in class to the U5).
    As there were no U7's available during this time, we went ahead with the build, hoping they would work for a RED payload.

    Testing:
    Carrying 20,000mah at 27lbs AUW, flight time was 12-13 minutes and the craft flew very nicely. Great for DSLR sized loads.
    At 33lbs. AUW (this is what it would be with a RED) flight time was 9 minutes, but yaw stability was compromised because the motors were operating near their limit. Any aggressive throttle inputs yielded adverse yaw effects.

    Motors and ESC's only slightly warm after all test flights.

    Now we are thinking about just getting an extra set of Gryphon folding boom arms and building them up with the U7 420 motors. We are using bullet connectors at the fold. We could switch arms depending on the load.
     
  8. Michael McVay

    Michael McVay Active Member

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    Tim and Bryan,

    For the A2, are you using the stock mixer (all top props spin one direction and the bottoms spin the other) or have you done a custom mixer so every other motor is counter rotating (like the way MK does the X8)?

    Michael
     
  9. Tim Gould

    Tim Gould New Member

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    Stock mixer. Have you found that you like the MK style better? I suspect it may help the slight yaw when bumping the throttle.
     
  10. Michael McVay

    Michael McVay Active Member

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    I think it definitely helps with the yaw authority. I tried flying a HoverFly board on one of my X8 builds and the yaw became a pretty big problem to the point where I had to get a hold of HoverFly tech support to talk to them about it. They too spin all the tops one way and the bottoms all spin the other way. Essentially they told me they prioritize pitch and roll over yaw and in certain scenarios you just run our of motor overhead to control everything so they let the copter yaw and keep it level - especially as it relates to the direction the bottom props spin (assuming you are using the same props top and bottom) since they have less "bite" and probably hit their max quicker.

    For my most recent X8 I went DJI and used the attached mixer. I prefer counter rotating tops and bottoms. I think you might find it helps get rid of the yaw issues for you.
     

    Attached Files:

  11. Dave King

    Dave King Well-Known Member

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    Bryan did you note what the hover throttle was without AH? That's the true measuring stick to see how much power the motors have for any given weight.
     
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  12. Tim Gould

    Tim Gould New Member

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    At 33lbs., non-attitude mode I was hovering around 72%.

    I will probably give the custom mix a try not so much for a solution to the marginal power, but for a more symmetric arrangement.

    Those of you who have used Xoar and T-motor props, do you feel the upgrade to T-Motor carbon props was money well spent?
     
  13. Shane Moore

    Shane Moore Member

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    I calculated the efficiency loss by time in the air over multiple runs with one 9000 ma 6S battery. With everything the same except X8 or flat 8 I had an average of 6 minutes until voltage hit 21.3 and the average was over 8 minutes for flat 8. Any suggestions for what I might try to improve efficiency of the X setup?
     
  14. Dave King

    Dave King Well-Known Member

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    72% isn't going to cut it. I saw about 6-8% decrease in hover throttle going from 16X5 Xoar to 16X15.4 Tiger props.
     
  15. Tim Gould

    Tim Gould New Member

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    Dave,

    Thanks for the feedback. That may not get us where we want, but that is still a fair gain.
     
  16. Howard Dapp

    Howard Dapp Active Member

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    Someone should direct KDE to this thread. Maybe they'll be happy to make some suggestions.
     
  17. Kari Ylitalo

    Kari Ylitalo Member

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    Just my two cents but i was fist planning to use U7 in Gryphon foldable coaxially with them but i did feel folding mechanism bit uncomfortable for heavy motors and big props. As it's not "one piece" design but sort of glued from the end of CF tube to the aluminium block don't know how long it would last with spinning and vibrating motors and props. I didn't want to live thinking to lose the arm in air so went other route and did own foldable frame which is rock solid without any possibility to come apart mid flight.
     
  18. Howard Dapp

    Howard Dapp Active Member

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    Speaking of props, just recieved a set of Tiger 17x5.8 and 18x6.1 gosh they're like jewelry. The 17" are actually 2g lighter than Xoar 16" props plus a heck of a lot less fragile and from what I hear they're better performing...just a tad bit on the expensive side!

    image.jpg
     
  19. Steve Maller

    Steve Maller UAV Grief Counselor

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    Where'd you find these in stock? They're really hard to find these days.
     
  20. Howard Dapp

    Howard Dapp Active Member

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    Steve, Getfpv. Looks like they're out of the 18"
     

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