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Old Oct 12, 2011, 10:07 AM
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possible asymetric quadplus? bi-copter with stabilization rotors instead of tilt?

Hi,
is it possible to build and fly an asymetric quad plus?
I want the front and rear rotors to carry all/most of the weight (like a BI-copter) To compensate torque, these need to pair CW and CCW.

The difference to BI is I do not want to tilt the main motors/rotors but
for stablization etc. it will have two little left/right rotors for roll. As these run with small props, torque should not be that much of an issue but for sake of symetry I would opt for a pair of CW and CCW again.

Rotor sizes would be in my case something like 6 and 10 inch rotors (and two small and two large motors).

The rotation would have to be as in the diagram to compensate for torque, right? This does not follow the rule of thumb provided for quads.

What do you think, possible, been done?
The problem I see is with yaw?

(This question was asked earlier in the multiwii thread but I think it deserves a broader range of experts to discuss)

If you ask why go this way and not choose the proven quad-plus or quad-x all I can say is: because a) it is possible (maybe) and b) to bypass obstacles when flying in narrow space.
Thanks, Hamburger
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Old Oct 14, 2011, 02:36 AM
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come on!
No response yet meaning 'cannot be done' or 'has been done, boring' or what?
Give me a hint at least, please.
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Old Oct 14, 2011, 02:48 AM
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Interesting idea but CW prop on front and CCW on the rear isn't possible because you'll end up with props spinning in the same direction that are adjacent vs opposite to each other. Any yaw will cause it to destabilize and crash because, in order to rotate CCW, the CW props need to speed up and CCW props slow down (and vise versa).

Placing CCW props on front and rear, and CW on sides would work but you end up with the smaller motors/props being over worked and really weak yaw in one direction.
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Old Oct 14, 2011, 02:58 AM
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This makes me think about the CH-47 Chinook, ala multi-rotor.
It seems much complex to built a solution with fixed props (no blade orientation) than the legacy bi-rotor heli is.
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Old Oct 14, 2011, 03:59 AM
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Quote:
Originally Posted by patricklupo View Post
Interesting idea but CW prop on front and CCW on the rear isn't possible because you'll end up with props spinning in the same direction that are adjacent vs opposite to each other.
well, if it was a true BI-copter, the two rotors must rotate CW and CCW in order to avoid constant yaw from momentum, right?
As a second step I need something to stabilize roll, that is where the two small rotors come in (again CW and CCW).

I assume that pitch (increase lift for either front or tail rotor) will work as with usual quad-plus.
So pitch and roll should be covered.
Now to something completely different:
Quote:
Any yaw will cause it to destabilize and crash because, in order to rotate CCW, the CW props need to speed up and CCW props slow down (and vise versa).

Placing CCW props on front and rear, and CW on sides would work but you end up with the smaller motors/props being over worked and really weak yaw in one direction.
I agree that yaw is the achilles heel of this setup.
On your standard quad-plus you yaw left by increasing front+tail CW-pair and decreasing left-right CCW pair and use momentum difference while maintianing constant overall lift.
In my intended setup the CW props are front and left, if I increase those two and decrease the other two then I get tilt with left+front raise. For the other yaw direction I do net get right-front raise but right-tail raise. Not good!

So maybe I should build a hex instead of a quad:
large BI with superimposed quad-x
front and tail - two big rotors mainly for lift, not used for yaw (CW+CCW)
4 small rotors (two on each side) for roll and yaw. ((2 CW + 2 CCW as with a quad-x)

Sound reasonable?
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Old Oct 14, 2011, 04:42 AM
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sounds feasible but i really don't know
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Old Feb 05, 2016, 12:16 PM
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You can do this with OpenAero VTOL

Quote:
Originally Posted by hamburger View Post
Hi,
is it possible to build and fly an asymetric quad plus?
I want the front and rear rotors to carry all/most of the weight (like a BI-copter) To compensate torque, these need to pair CW and CCW.

The difference to BI is I do not want to tilt the main motors/rotors but
for stablization etc. it will have two little left/right rotors for roll. As these run with small props, torque should not be that much of an issue but for sake of symetry I would opt for a pair of CW and CCW again.

Rotor sizes would be in my case something like 6 and 10 inch rotors (and two small and two large motors).

The rotation would have to be as in the diagram to compensate for torque, right? This does not follow the rule of thumb provided for quads.

What do you think, possible, been done?
The problem I see is with yaw?

(This question was asked earlier in the multiwii thread but I think it deserves a broader range of experts to discuss)

If you ask why go this way and not choose the proven quad-plus or quad-x all I can say is: because a) it is possible (maybe) and b) to bypass obstacles when flying in narrow space.
Thanks, Hamburger
Its 2016 and you can do this with KK2.1 and OpenAero VTOL
Check this thread, download the manual and read.

http://www.rcgroups.com/forums/showthread.php?t=1972686

Cheers
Nicholas
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