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Old Oct 07, 2012, 03:40 PM
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Originally Posted by Del-Dredd View Post
May not be CoG of frame but is Center of lift and where you want CoG to be as that is also the center or pivot moment ie where the craft will pivot around when banking, pitching and yawing.
So, as the back motors gets closer by design, the centre of lift moves further back?
Centre of lift will be on frame centreline halfway between back and front motors. Since back motors are tilted, it will actually be further forward, assuming all motors produce same thrust.

Fred
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Old Oct 07, 2012, 03:52 PM
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Vtail COG

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Originally Posted by rcjose View Post
This is what I meant about placing a line from motor to motor. Where the lines meet in the middle is the center of gravity and indicates where the controller should go.

Because the photograph is not taken from directly overhead, the angles of the lines are wrong so the COG is wrong as shown by the lines but you get the idea.
Ohh ! I got it...I was not really aware of that and thanks for clarifying that.I will do that and place the controller on the center of the X...I did checked the COG and it's like 2" to the front on your pix...thanks again and I will keep you posted.
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Old Oct 07, 2012, 04:17 PM
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Originally Posted by flarssen View Post
So, as the back motors gets closer by design, the centre of lift moves further back?
Centre of lift will be on frame centreline halfway between back and front motors. Since back motors are tilted, it will actually be further forward, assuming all motors produce same thrust.

Fred
Yes, the center will go farther back the closer the rear motors are together. That's a good point about the rear motors since some vtails use different size props in the back and therefore will produce different thrust. I see what you mean about the motors titlted causing the center to move as well.

Too bad the only real way of finding out is to build it a certain way and hopefully not end up in a crash.
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Old Oct 07, 2012, 04:18 PM
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Originally Posted by COCO2010 View Post
Ohh ! I got it...I was not really aware of that and thanks for clarifying that.I will do that and place the controller on the center of the X...I did checked the COG and it's like 2" to the front on your pix...thanks again and I will keep you posted.
Good luck. I have always wanted to build a v-tail. Maybe one day.
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Old Oct 07, 2012, 04:31 PM
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Originally Posted by COCO2010 View Post
Ohh ! I got it...I was not really aware of that and thanks for clarifying that.I will do that and place the controller on the center of the X...I did checked the COG and it's like 2" to the front on your pix...thanks again and I will keep you posted.
I wouldn't worry too much about controller placement. At least wait until you've watched my recording from today. As you know I have my KK2.0 located up front on my VTail frame and it flies perfectly (if I may say so myself).

This short recording was filmed during perfect weather conditions with auto level disabled. I just hope you forgive me for using DropBox instead of YouTube. You may have to download the movie file (175MB) to get stutter-free playback.

https://dl.dropbox.com/u/68787338/VC-VTail.mp4

I did try auto level today, but it needs some adjustments. It worked quite well with my Quadrino so I believe I can make it work on my KK2.0 as well.

Feedback on my video will be appreciated.
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Old Oct 07, 2012, 04:41 PM
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Don't you want to CoG of the 'copter to line up with the center of thrust? With tilted rear rotors the back motors are contributing less vertical thrust so the center of thrust would move forward.

The geometric approach is only accurate (I think) if you have all motors in the same plane, with the same properties (e.g. Kv, prop, ESC, etc.).

Come to think of it, your diagram won't work, if you reduce the V tail to a tricopter the lines wouldn't cross.

<Hypothesis on>
I must say, I'm still a little puzzled about the extent to which levelling and calibrating flat is required. I would have thought that once you were flying (or had it trimmed to zero) then the flight controller could care less and would adjust the motors to keep things "right" regardless (of their specs). You would only get into trouble if one of the motors couldn't deliver the required thrust (or torque reaction). I guess this would only work if you had an "auto level" type control algorithm working, with a rate control one changing the throttle would shift the trim.
<Hypothesis off>
I'd sure appreciate knowing if & why I'm off base?

cheers,
Andrew
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Old Oct 07, 2012, 04:43 PM
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Originally Posted by RC911 View Post
I wouldn't worry too much about controller placement. At least wait until you've watched my recording from today. As you know I have my KK2.0 located up front on my VTail frame and it flies perfectly (if I may say so myself).

This short recording was filmed during perfect weather conditions with auto level disabled. I just hope you forgive me for using DropBox instead of YouTube. You may have to download the movie file (175MB) to get stutter-free playback.

https://dl.dropbox.com/u/68787338/VC-VTail.mp4

I did try auto level today, but it needs some adjustments. It worked quite well with my Quadrino so I believe I can make it work on my KK2.0 as well.

Feedback on my video will be appreciated.
VERY nice sir. Love the music to
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Old Oct 07, 2012, 04:50 PM
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VERY nice sir. Love the music to
Thank you! Glad you liked it.
Music: Yngwie Malmsteen (Swedish metal guru).
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Old Oct 07, 2012, 05:16 PM
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Originally Posted by rcjose View Post
Yes, the center will go farther back the closer the rear motors are together. That's a good point about the rear motors since some vtails use different size props in the back and therefore will produce different thrust. I see what you mean about the motors titlted causing the center to move as well.

Too bad the only real way of finding out is to build it a certain way and hopefully not end up in a crash.
LoL !

Sorry again. But Fred is right. Center of Lift is always half way of motordistance. Otherwise it would be impossible to level the Copter horizontally in Flight (assuming CoL = CoG).
But I am sure you know. Your Theory of line from Motor to Motor is ok for symetrically built Multicopters. Asymetrically built Copters are a little bit more complicated in Theory. And if you go on with Yaw-Movements and Forces, it is f...g complicated to calculate all this in Theory. Believe me. We are discussing all this with a few mathematicians in the university. Dynamic flight physics is heavy stuff! :-)
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Old Oct 07, 2012, 06:10 PM
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Originally Posted by RC911 View Post
I wouldn't worry too much about controller placement. At least wait until you've watched my recording from today. As you know I have my KK2.0 located up front on my VTail frame and it flies perfectly (if I may say so myself).

This short recording was filmed during perfect weather conditions with auto level disabled. I just hope you forgive me for using DropBox instead of YouTube. You may have to download the movie file (175MB) to get stutter-free playback.

https://dl.dropbox.com/u/68787338/VC-VTail.mp4

I did try auto level today, but it needs some adjustments. It worked quite well with my Quadrino so I believe I can make it work on my KK2.0 as well.

Feedback on my video will be appreciated.
All i can say is WOW! That thing looks so wicked in the air, especially the way it turns. Very smooth!! Did you build the frame yourself or did you buy it somewhere?

That is one great build you have!
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Old Oct 07, 2012, 06:30 PM
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All i can say is WOW! That thing looks so wicked in the air, especially the way it turns. Very smooth!! Did you build the frame yourself or did you buy it somewhere?

That is one great build you have!
Thank you! I actually used QUAD frame parts (VC-450 and VC-550) from www.hoverthings.com for this build, 'removed' one arm and added the 'V'. Just as simple as that.
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Old Oct 07, 2012, 06:30 PM
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"Come to think of it, your diagram won't work, if you reduce the V tail to a tricopter the lines wouldn't cross."

You dont neccesarily have to cross lines, a better analogy would be the center will be roughly the same distance from each motor, so does not matter if 2, 3, 4 or more.
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Old Oct 07, 2012, 06:46 PM
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Quote:
Originally Posted by RC911 View Post
I wouldn't worry too much about controller placement. At least wait until you've watched my recording from today. As you know I have my KK2.0 located up front on my VTail frame and it flies perfectly (if I may say so myself).

This short recording was filmed during perfect weather conditions with auto level disabled. I just hope you forgive me for using DropBox instead of YouTube. You may have to download the movie file (175MB) to get stutter-free playback.

https://dl.dropbox.com/u/68787338/VC-VTail.mp4

I did try auto level today, but it needs some adjustments. It worked quite well with my Quadrino so I believe I can make it work on my KK2.0 as well.

Feedback on my video will be appreciated.
How come I click on the link and it won't show your video?
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Old Oct 07, 2012, 06:47 PM
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Originally Posted by Del-Dredd View Post
"Come to think of it, your diagram won't work, if you reduce the V tail to a tricopter the lines wouldn't cross."

You dont neccesarily have to cross lines, a better analogy would be the center will be roughly the same distance from each motor, so does not matter if 2, 3, 4 or more.
Which sounds like you would agree that a spider frame's center of lift is going to be pretty close to the midpoint between the forward and aft motors (if we ignore complex flow interaction for the moment), yet earlier it seemed like you were in agreement with divination by string geometry?
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Old Oct 07, 2012, 06:48 PM
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How come I click on the link and it won't show your video?
It requires a browser plug-in, but I recommend downloading the file anyway and play it locally. Hope you'll like it.
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