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Old Jul 13, 2011, 11:13 AM
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VTOL - Tilting rotor shaft?

Hi,

I have a MAV system that has a concept of using gimballing of the rotor head to provide offset of the thrust axis from the centre of gravity to provide restoring forces to effect stability and lateral flight control. I'm trying to put together a system model but I am having a hard time since I don't know how to account for the tilting of the rotor head for flight control? I can't find any research papers of other people using the same idea :/!

Any help?

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Old Jul 13, 2011, 04:47 PM
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It has been used in pitch for two rotor VTOL models, the considerations are pretty much the same. You can use the tilt to obtain control, but you won't obtain a stabilizing effect from it, only a control mean. You will have to implement other methods to obtain a self righting platform
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Old Jul 15, 2011, 08:08 AM
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Quote:
Originally Posted by Brandano View Post
It has been used in pitch for two rotor VTOL models, the considerations are pretty much the same. You can use the tilt to obtain control, but you won't obtain a stabilizing effect from it, only a control mean. You will have to implement other methods to obtain a self righting platform
Could you point me to where the documentation for those 2 models are? I can't find them, and I'm quite stuck :/
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Old Jul 15, 2011, 10:56 AM
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not two models, models with two rotors
see this thread, for example: http://www.rcgroups.com/forums/showthread.php?t=1470649
it does in pitch what you want to do in both pitch and roll, if I understood your layout.
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Old Jul 29, 2011, 09:05 AM
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Quote:
Originally Posted by Brandano View Post
not two models, models with two rotors
see this thread, for example: http://www.rcgroups.com/forums/showthread.php?t=1470649
it does in pitch what you want to do in both pitch and roll, if I understood your layout.
You have linked my original post?
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Old Jul 29, 2011, 10:48 AM
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oops, sorry, my bad. I meant this one: http://www.rcgroups.com/forums/showthread.php?t=1397409
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Old Aug 03, 2011, 02:43 PM
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My Build VTOL

Hi all , I build my VTOL w. two Rotors only with the KKmulticopterboard from Minsoo Kim. A great programmer in Taiwan.
http://www.kkmulticopter.kr/

FC Board here : AVATAR Board http://www.kkmulticopter.kr/index.ht...02_tw&id_no=57

Motors running, hovering works , but have to adjust the Yaw Pot and Testing it. Motors are mount on a Mechanic with a Servo, he moves the complet Motor/ Prop.
Sincerly Mike
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Old Aug 08, 2011, 08:17 AM
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Hi guys, thanks for the help.

I'm still working on this and I've come to the conclusion the current design will not work (allowing the head to wobble to maintain roll stability, tilting the center of gravity). I'm finding it hard to prove that this will not work (so I can go on and design a better system). I don't know how to 'add' the tilting center of gravity to any control equation or the AB matrix.

If I can find out how to add this to a numerical control matrix (for example the AB matrix) I believe I can use matlab to show that it will not work.

The reasoning behind the gimballed device was that from a consideration that if the platform was given pendular stability (centre of gravity placed well below the thrust generating rotor head) the thrust axis could be tilted with respect to the centre of gravity to provide stabilisation and a side force with respect to upsets caused by side winds and gusts.
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Old Aug 08, 2011, 11:04 AM
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That very same control concept is implemented in the Airscooter Ultralight coaxial helicopter. http://www.airscooter.com/pages/airs...edia_files.htm

The company tried to design a hobby model for production based on the weight shift principle like the ultralight version. Through several versions of prototypes, could not get enough vertical cg differential for the size rotor required for lift to give adequet controls response and stability. Not enough lower mass, even attaching batteries to the skids, to counter the inertia of the rotors.
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Old Aug 08, 2011, 04:04 PM
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You can achieve control via CG shifting, but not stability, It will however be stable if you use an articulated rotor with a flybar or another form of gyroscopic stabilization. Just think about the plethora of small coax remote control helicopters. The price to pay, however, is reduced speed.
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Old Aug 08, 2011, 05:04 PM
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You could also achieve stability by using an FMA Copilot, but you would be limited to outdoor flight only. It is very simple to setup and use and works very well.

It maybe helpful to keep in mind that stability needs a reference point, either from a gyro, infrared detection as in the FMA Copilot or a human pilot input into the controls.

Kelly
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Old Aug 11, 2011, 11:04 AM
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What I'm looking at at the moment is the dynamic model (which is a pain in the butt), I don't really care about the electronics or anything to do with the physical model yet. I understand how the concept uses the tilt to obtain motion, but I'm struggling to put in down on paper (the maths part). Im trying to re-derive the equations of motion, using an inverse pendulum with a similar weight of my device mass. Once I have this, I will move on to hopefully create my A and B matrix prototypes.
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