Cinestar X8 Coax Updated

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

  1. Howard Dapp

    Howard Dapp Active Member

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    I use square tube so no problem. For round tube both motors will share the same tube clamps fixed to individual motor mounting plates so no problems there either.
     
  2. Dave King

    Dave King Well-Known Member

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    I never thought about that. Anyone have any pictures of one of the booms showing the tube clamps?
     
  3. Jason Toth

    Jason Toth Active Member

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    The motors are counter rotating and act like mini gyro stabilizers + the flat props act like a large plane and is more effected by cross winds. This is just my opinion/observation but like Howard stated, once you fly a Coax... a flat seams floaty - try it for yourself :)
     
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  4. Brad McGiveron

    Brad McGiveron Active Member

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    Like the others say... there is a very noticeable difference.

    If you have flown single rotors then it is quite similar to the difference between flybar and flybarless. An old school flybar heli feels kinda floaty where as the flybarless feel locked in/planted and on rails and does exactly what you tell it.
    The X config feels very planted where as the flat feels sort of planted and a little wishy washy.
    Once you try it and get it sorted you will be hooked.
     
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  5. Steve Maller

    Steve Maller UAV Grief Counselor

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    I just removed the press nuts from one of the two motors and run screws through both motors.
    motors.jpg
     
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  6. Shaun Stanton

    Shaun Stanton Active Member

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    I agree 100% the wind resistance is far superior to the flat 8. I will take a minute lost over having a far superior descent profile to the flat 8. I cant think of a reason why you would want a flat 8 now other than a bit of more flight time. But the world we are in is about dynamic performance and the capability we can do with that. If you want a long steady shot than get a crane. Even then a crane shot is less than 5 seconds more than enough for me to get in a cinestar. When I flew the falt in gusty wind it would wind vane. Now its as solid as a rock!!

    I cant agree enough if tuned right the coaxial is far superior than anything the flats can provide they are the bomb!! I mean I was getting 13 feet per second from a decent with just minimal shaking. The throttle response shunted it quick.

    Once I have gone Coax ill never go back!!!!
     
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  7. Dave King

    Dave King Well-Known Member

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    wow thanks for the feedback. What about setting up the mixer for a HL? I have no idea how to do it or know how hard it is?
     
  8. Dave King

    Dave King Well-Known Member

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    I was reading up on some other Coax threads here and I seen some concern about the X4 in conjunction with the 3 axis gimbal with potential of seeing the bottom blades in the shots. Brad, Howard, Shaun or anyone else do you have any experience with this and no if its a factor? Is the stock CS8 frame strong enough to support the torque with just upgrading the clamps?

    Sorry to hi-jack the thread Steve.
     
  9. Ozkan Erden

    Ozkan Erden Distributor

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    When using 3-axis gimbal with 2nd operator, that's one of the problems we are facing with X8 setups. My camera operator is more happy with flat Octo since he captures the props less.

    With 2-axis gimbal and single man operation, you have more clearance though.
     
  10. Howard Dapp

    Howard Dapp Active Member

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    Has not been much of a concern for us at all, you fly with that in mind and all your shots are planned out. In fact, if you have a shot where you need to look up 110-130 degrees, there is enough clearance in between the two front arms/motors to pull that shot off at 24mm or so..cant do that with a flat layout.

    You start out 20 feet or so in front of a 100 foot tall statue, camera looking up 130 degrees, you slowly climb the while still looking up, as you reach the chest/neck area your operator slowly starts to tilt down. As you pass the statue's face you're at 90 degrees, as you climb beyond the head you're looking directly down at the statue....nice.
     
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  11. Dave King

    Dave King Well-Known Member

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    What's easier to get in the shot? Boom 1 on a flat 8 or lower props on X8?
     
  12. Steve Maller

    Steve Maller UAV Grief Counselor

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    Not hijacked at all, Dave!

    For those using the Avroto 3520 motors, what are you using for motor mounts? Especially in a X8 config.
    Looks like it’d have be be something different than the standard Freefly-type boom clamps.
     
  13. Howard Dapp

    Howard Dapp Active Member

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    Dave it depends. That certainly shouldn't be a deciding factor. Booms/motors in shots are far more easy to prevent/avoid than keeping a rig steady for a shot in wind.
     
  14. Shaun Stanton

    Shaun Stanton Active Member

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    I find that it depends on what the shot profile is and how wide you are shooting. To quantify you have 10 degrees less freedom of movement to where you may capture the tip of the motor bolt worse case scenario. This being if your gimbal is directly in front of the axis of a boom.

    Where this maybe more problematic is in wide panoramic shots where you are trying to slew the camera across the horizon especially if you have a front heavy camera and need to bring it back, then you will more likely get a motor/s in the shot especially if the copter is in position hold and compensating for wind.

    But then at the same time if you are shooting real wide like less then 20mm for example I find that I can get adjacent booms in the shot regardless. So it is a double edge sword. A flat 8 you have more booms likely to be exposed in the shot but you have a little more freedom of movement in the tilt. The X configuration you may be less likely to get a boom in the shot probability wise if the copter is not compensating for wind but more likely to get it in the shot when it is compensating for a quartering wind, such as a wind coming from a 45 degree direction into where you are shooting from.

    My take on it is that I find that I am more likely to get the boom in the shot on a flat 8 when doing a run towards a target like following a car down the road at low altitude and getting the initial start. Here I have to try plan a running start getting the copters momentum going then relaxing the stick a bit until I start to climb. With the X8 config I this wont be an issue anymore. I find this to be very advantageous.

    In fact if planned right I think you have more freedom of movement to get higher tilt angles on shots you will never get on flat 8's because now each boom is separated by 90 degrees versus 45 so there is less of a chance to get adjacent booms in the shot.

    So I think if planned right you can easily mitigate or even take advantage of the few short comings from the X config.
     
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  15. Shaun Stanton

    Shaun Stanton Active Member

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    Dave

    The mixer is fairly straight forward what you are doing is assign which motor is going to affect which axis. they go from 0-64 but you can assign a higher value like 71 for example on the bottom motors as in the MK site. There is a lot of debate on whether or not this mixer is a good one. I have seen other techniques and suggestions on other sites as to whether or not you need larger props on the tops or bottoms or coarser props. No one seems to have a quantified consensus on this. And will probably spur some discussion by me even mentioning it.

    Anyway if you look at the mixer for the flat 8 you will see some motors like 1 and 5 have 0 for roll and motors 3 and 7 have 0 for pitch in the +8 config. This is because those motors provide no moment for those axis's. But in the X config they will value corresponding to the position of the motor. If left of the Y axis they will be +64/71 for roll and Negative if on the right side. Conversly for Pitch all motors forward of the X axis are given a +64/71 and -64/71 Aft of the X axis. Any motor spinning Clockwise gets a "+" for yaw and a "-" for Counter clockwise.

    The assignment addressing for which motors you physically connect to which BL is arbitrary as long as you assign the correct mixer for that motor. Here is an example from the MK site.

    [​IMG]

    They assigned the top motors as 1 2 3 and 4 in cross pattern and the bottom motors 5, 6, 7 and 8. I did mine a little different I made my top motors 1,3, 5 and 7 and the bottoms the even complement going in clockwise direction starting from the front right boom. It does not matter as long as that BL connected to the motor is mixed right. This will work, it seems to be fine for me although I use 71 on the tops my thought is that I want more air from the top to push down through the disrupted airflow from the bottom, and it seems to work fine although I am still in the experimentation stages. So I am not advocating what I have done so far and maybe someone has some further insight.
     
  16. Steve Maller

    Steve Maller UAV Grief Counselor

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    Thank you, Shaun. I always feel a little smarter when you write a post. :D
    Are you using the same props top/bottom?
    I am using 14” APC MR props on both.
    I tried 16” APC MR on the bottom at 64 in the mixer, and the BLs were running too hot, but I may try the 16” again on top as per your thoughts. I was also about 1 LB heavier at that time (test payload of LiPos) so that might be the issue.
    I’m seeing current draws about 20% higher on my bottom motors using the 64 top/71 bottom mixer as per MK. I’m going to test some different values today.
     
  17. Shaun Stanton

    Shaun Stanton Active Member

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    Thanks, but I am not advocating what I am doing is correct, as there ton of back and forth on this subject. To answer, right now I am using the standard 14 APC Slow flys for both. But, it would seem to me unless someone has some better insight, I am not an Aero/MechE.. It would seem that having larger prop on the bottom would make the top work harder because that air would in theory be shunted by the bottom rotor disc almost making the top air not productive. I saw someones explanation a while back that seemed to make some sense on the subject I wish I can find it now. But the idea is that if the prop on top is spinning faster then it will allow for that air in theory to meet the air from the bottom at the same time causing a collision of sorts. I essence making pseudo ducted fan without the duct. an allowing the column of air to push down with more pressure. I think it makes sense at least that the top air has more force to go through the bottom prop as the the bottom prop is a big windbreak to the top possibly.

    So far there have not wind tunnel test to quantify this. But it never hurts to try the big one on top and see what happens. At least we will know if it has any credence. Like you I will be trying different setups as well and see what the best results are. The problem you may running into is that the QC motors are not suited for 16's and may need to dial down to 15's and see if that makes any improvement. The 16's could be forcing the QC 3328 to work harder at a lower RPM causing the BL's to heat up.
     
  18. Steve Maller

    Steve Maller UAV Grief Counselor

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    Shaun, my evidence certainly indicates that with the 16” props the BL temps were higher than I was comfortable with, considering the ambient temps and the load I had on them. But I think I’ll try them on top instead and see what happens.
     
  19. Dave King

    Dave King Well-Known Member

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    Steve I see you are looking for motors, go with the U5's. The build quality on them is incredible and Quadrocopter has bullet connectors for them.
     
  20. Shaun Stanton

    Shaun Stanton Active Member

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    It will be interesting to see your results.
     

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