Cinestar X8 Coax Updated

Discussion in 'Cinestar 8' started by Steve Maller, Dec 23, 2013.

  1. Steve Maller

    Steve Maller UAV Grief Counselor

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    Going to make another attempt at configuring my Cinestar 8 as an ‘X8’ coaxial. This configuration places two motors on each of 4 booms. There is ample evidence that this configuration is more stable than the “flat 8”. It also allows me to shoot video straight ahead without getting the front boom in my shots.

    I got her up in the air for the first time today, and she flew very nicely. I am flying 14” APC MR props on the top motors and 16” APC MR props on the bottom motors. My mixer config is set to 64 for all motors. I’m running standard MK stack and QC motors.

    I was flying at an AUW of 16.25 lbs, about 2.5 pounds heavier than I normally fly. It handled well. But my current consumption is about 50% higher than at my normal AUW with the flat config. Of more concern is my BL temps which spiked to 100°C on a previous flight with the NC disconnected (based on the Fraulein’s pronouncements). Ambient temperature was 50-55°F. Flying around dropped the temps, but hovering definitely spiked the temps to an uncomfortable level, even in this cool air.

    I wanted to test this weight because this is the likely weight of the copter with the brushless gimbal and 5D Mark III.

    So here’s my question...

    Obviously there are several variables at play (X8 vs. flat, AUW, and different props/mixer config). Does anybody know how I can accurately model this config in Ecalc to play with how I can optimize this configuration?

    Here’s the GPX file and a couple videos...thanks!

     

    Attached Files:

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  2. Dave King

    Dave King Well-Known Member

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    Steve why don't you try the fan mode? It really works! It's a cheap mode and if it doesn't work your out $25 bucks. I really think the QC motors are way out of their efficiency range starting around the 6.5-7KG range. I would consider going with the new Navigator 3515 motors or the Avarto 3515 motors. It should help make your setup much more efficient. Only catch is that trying to go to any different motor will probably make you switch to 6S batteries.
     
  3. Ozkan Erden

    Ozkan Erden Distributor

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    Short answer: You can't model it on ecalc yet. What I do is to calculate the values with 20% efficiency difference in mind.

    My thoughts on X8:

    I can't find X8 efficient. You have less battery time / more battery consumption /less lifting capacity; whatever you name in terms of inefficiency over flat octo.

    I have tried X8 octo over flat octo many times and every time I reverted back to flat octo for more flight time.

    I have a setup similar to yours (MK setup). With brushless gimbal, 5D MK III + 24mm lens and 10A 4S Lipo, flight time is around 5.5 safe minutes. But the load on the Lipo with 770KV motors and 14" props are quite worrying. This is a flat Octo setup. While I'm at the limits and If I change it to X8, I would have 4 minutes flight time with the exact same equipment.

    There is no way that X8 can be more efficient over flat octo in terms of battery consumption & flight time. For my setups, the difference is around 20%. So, for the copters which are at the limit, changing to X8 will be quite stressful.

    So when modelling a X8 setup, find the values for flat octo, then add the 15%- 20% efficiency difference.

    Your 8 minute flight time will be around 6-6.5 min with the same payload
    OR to get the same flight time you will need to load %15-20 less payload
    etc.
     
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  4. Dave King

    Dave King Well-Known Member

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    Ozkan

    What motors are you using? Stock QC? If so I would imagine a motor change with 15" props and 6S batteries would make it very efficient?
     
  5. Ozkan Erden

    Ozkan Erden Distributor

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    Dave,

    I'm using Tiger MT2814 770KV, very similar to QC3328.

    Yes, definetely: I'm moving to 6S and Tiger U5 motors right now with 17" props. I will have to build this as an X8; 17" props with flat octo will be ridicilously big. Since this new rig won't be on the limits, I can sacrifice some efficiency over a big copter.
     
  6. Steve Maller

    Steve Maller UAV Grief Counselor

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    The conversation about flight times is not necessarily relevant to me. If I am able to get consistent 6-8 minute flights, I will be happy. I’m able to get 14 minutes or more with my current setup, but I rarely fly more than 5-6 minutes. To tell you the truth, I’m considering using a quad or hex for longer flights, as the Cinestar (in my mind) is a heavy lift, short haul platform (relatively speaking).
     
  7. Dave King

    Dave King Well-Known Member

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    I understand I just think the QC 3328's are way out of their efficiency range at 16 pounds that cause the higher power consumption and motor temps. I think for your flying weight the new Navigator 3515's are a good choice with the combination of 16" props.
     
  8. Steve Maller

    Steve Maller UAV Grief Counselor

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    I’m going to do some more testing today with 14” props on the bottom instead of 16”, and some mixer changes. I think the 4S QC 3328s and BL 2.0 ESCs just don’t have enough oomph to swing the bigger props. Those props look huge compared to the 14”. And my BL temps back that up. They were pushing perilously close to 100°C, which is too hot, especially in relatively cool weather.

    While I’m not terribly interested in building a big heavy lift copter like some of you, I would definitely like to be able to fly with a 3-axis brushless gimbal and a 5D Mark III with L glass. I figure that’s in the neighborhood of 8-9 KG AUW (18-20 lbs).

    I’m currently flying with a 2-axis with Radians, and I weighed it and my brushless gimbal today. The 2-axis brushless weighs about 2.5 lbs vs. 1.75 lbs for the Radian setup.
     
  9. Dave King

    Dave King Well-Known Member

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    I think the only way the 3328's and 4S system is going to work with 8-9KG is with a X12.
     
  10. Steve Maller

    Steve Maller UAV Grief Counselor

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    Yeah, not gonna go there. Trying to decide if I want to build a second copter or just upgrade this one. Might use my current CS8 electronics and motors, and pick up a CS6 frame as a backup to fly smaller cameras, then get the new MK electronics and motors for a heavier lift machine.
     
  11. Ozkan Erden

    Ozkan Erden Distributor

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    My 3 axis CS gimbal converted to brushless (5108 on roll and tilt, 8108 on pan) loaded with 5D MK III ad 24 mm weight around 7 lbs. My overall weight is again 18 lbs range with 3515 motors and single 8000 mAh battery. I would never try to lift this weight with WX or 2814 motors /w BL 2.0 controllers, as you saw it in your tests.

    A quad capable of lifting this weight can be built with U7 motors and 18" props. Even with a decent flight time. But, redundancy? No. Redundancy can be the only reason not to go with quad.

    ecalc-quad1.jpg
     
  12. Steve Maller

    Steve Maller UAV Grief Counselor

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    Just weighed my 2-axis BLG with the GH3 on it, and it’s 4.96 lbs. My copter sans gimbal with 2x8000 LiPo on board is 9.92 lbs. So I was actually flying yesterday in the test at probably the right weight to simulate the 5D Mark III. But truth be told, I am really, really happy with the GH3, so maybe this is a good interim solution.
     
  13. Steve Maller

    Steve Maller UAV Grief Counselor

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    It looks like my copter’s drawing about 82-84 amps when hovering in its current configuration. But how do I tell what the throttle % is? It feels like it’s working pretty hard, and the overall current draw is about 50% higher in the coax X8 config than it was in a flat 8. I’m wondering...
    • is my mixer config (64 uppers and 71 lowers) optimal for the APC 14” MR props?
    • are the APC MR props the wrong props for an X8? they worked great in a flat config.
    • should I go back to the flat 8 and investigate using a higher power system?
    Copter AUW is 15.22 lbs (6.9kg), about .6 pounds heavier than the copter was in its flat 8 config. Difference is the brushless gimbal vs. Radian gimbal. GPX file is attached. I was hovering in AH/PH on or around line 60.
     

    Attached Files:

  14. Howard Dapp

    Howard Dapp Active Member

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    yeah something isn't right. What mixer and size props (top/bottom) are you using?
     
  15. Steve Maller

    Steve Maller UAV Grief Counselor

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    As I mentioned above, mixer config is 64 uppers and 71 lowers and APC 14” MR props on both.
    I tried 16” APC MR props on the bottom and 64/64, but that didn’t feel very stable.
    Any other ideas?
     
  16. Howard Dapp

    Howard Dapp Active Member

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    yep, upgrade your system, get rid of those overly sensitive mk controllers, they cloud you with worry. It's time to go big boy with an HL setup. X8 is hands down more stable all around. I've only lost about 10-12% power but the stability gains are worth it hands down. If you have no desire to upgrade, switch to 5s...aren't mk controllers rated for 5s?
     
  17. Ozkan Erden

    Ozkan Erden Distributor

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    Yes, MK Bl Ctrl 2.0s are rated up to 5S but not optimized for 5s. It heats up very fast; so not safe to use with heavy lift. (Even with heatsinks applied).
     
  18. Dave King

    Dave King Well-Known Member

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    Hey guys can you tell me exactly why the X8 is hands down more stable? The only thing I don't like about the flat 8 is the GPS-position hold of the consumer grade GPS. My flat 8 feels very stable, are you talking about in heavy winds? Just curious.
     
  19. Howard Dapp

    Howard Dapp Active Member

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    Yes, heavy wind, calm winds even the yaw holds tighter. I've been flying X8 for about a year now and I recently flew a flat hexa and flat octo, I immediately felt the difference in stability, especially after flying a coax for so long. Flat just felt really floaty even with payload. In the same amount of wind the flat had to lean against it while the coax hovered flat. If I could compare in simple terms, the flat config felt like a sheet of note paper in free air while the coax feels like that same sheet of paper folded into a paper airplane.
     
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  20. Dave King

    Dave King Well-Known Member

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    Interesting. Must be difficult to square up the bottom motors?
     

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