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Old Aug 13, 2011, 05:11 AM
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Any info regarding this x8 setup?Better than coax x8?

I saw this x8 setup Name: GP_penta_air.jpg
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Description: In this thread:http://www.rcgroups.com/forums/showthread.php?t=1483594

And wonder if anyone out there has any information regarding this setup.

I have search on octo x8 but haven't found anything.I think this setup should work better than a coax x8,because the props may not disturb each other in same way because the upper engine is placed more too the center of the copter (correct me if I'm wrong)

What controller support this?Mikrocopter?Other's?
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Old Aug 13, 2011, 05:14 AM
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Anything with a custom mixer will support it.
And you're right about propwash.
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Old Aug 13, 2011, 05:34 AM
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Originally Posted by timecop View Post
Anything with a custom mixer will support it.
And you're right about propwash.
I don't know. I think you don't need anything really fancy. Just a normal octo capable board may do it.
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Old Aug 13, 2011, 05:35 AM
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Originally Posted by timecop View Post
Anything with a custom mixer will support it.
And you're right about propwash.
What is a custom mixer?Do you mean that you have to set it up yourself in some
controll program(like openpilot,ardcopter,mikropcopter and similar have)does't there exist any ready made setup program?(sorry if the question seem's dumb I'm little new too this...).

Another thing I was thinking of why does't you see this setup,If it's now better(?) than
coax x8.What is the down side?
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Old Aug 13, 2011, 05:44 AM
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Custom mixer will allow you to specify how any of the motors are affected by the 4 basic flight control values (roll/pitch/yaw/throttle). This is usually shown in terms of percentage, etc. Openpilot and MK can both do this inside their standard setup program.
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Old Aug 13, 2011, 05:58 AM
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Originally Posted by timecop View Post
Custom mixer will allow you to specify how any of the motors are affected by the 4 basic flight control values (roll/pitch/yaw/throttle). This is usually shown in terms of percentage, etc. Openpilot and MK can both do this inside their standard setup program.
Thank you Timecop for the explanation!

If anyone could link too a construction or some more info, it would be nice
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Old Aug 13, 2011, 06:04 AM
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To get an equal CW/CCW directions yawing, you should have to associate 2 inner props with 2 outer props to balance the combined moments (2LENGTHs+2lengths).
To achieve more yawing response, PhotoShip seems to use small angular pieces, as motor mount, to increase the tangential/diametral yawing thrust.
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Old Aug 13, 2011, 09:39 AM
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You will get excellent performance for an octo in any form even on a FCB that does not use mixing for each of the eight motors. A PID tunable quad board made into an octo with y-servo cables to duplicate the motors on each axis will fly just fine with failsafe redundancy.
Cheers,
Jim
Quadrocopter and Tricopter Mega Link Index
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Old Aug 13, 2011, 03:43 PM
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Originally Posted by Coptaire View Post
To get an equal CW/CCW directions yawing, you should have to associate 2 inner props with 2 outer props to balance the combined moments (2LENGTHs+2lengths).
To achieve more yawing response, PhotoShip seems to use small angular pieces, as motor mount, to increase the tangential/diametral yawing thrust.
In a yaw you are increasing speed on four motors with same rotation direction and reducing speed on the other four. If the motors of the same rotation on the top and bottom are arrange in a diagonal manner the lift should be the same and there will be no induced motion on any other axis.

Just think of an X8 like two quads.

Let's say the left front and right rear arms has all the motors (top and bottom) rotating clockwise. In a left yaw you will increase all four motors on the left front and right rear arms. Even if the top and bottom motors are NOT rotating in the same direction on the same arm. You will still have to increase speed on four motors. Two for the top and two for the bottom.

The only situation I can think of that mixing is required is when all the propeller spin one way on the top and spin the other way on the bottom. Then you will have yaw that reacts differently between right and left because one way you have longer arms and the other way you have shorter arms.
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Old Aug 14, 2011, 07:50 AM
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In a yaw you are increasing speed on four motors with same rotation direction and reducing speed on the other four. If the motors of the same rotation on the top and bottom are arrange in a diagonal manner the lift should be the same and there will be no induced motion on any other axis.

Just think of an X8 like two quads.

Let's say the left front and right rear arms has all the motors (top and bottom) rotating clockwise. In a left yaw you will increase all four motors on the left front and right rear arms. Even if the top and bottom motors are NOT rotating in the same direction on the same arm. You will still have to increase speed on four motors. Two for the top and two for the bottom.

The only situation I can think of that mixing is required is when all the propeller spin one way on the top and spin the other way on the bottom. Then you will have yaw that reacts differently between right and left because one way you have longer arms and the other way you have shorter arms.
Thanks for the all answers! It seems it be very rare do to a setup like this.

What I think it's great with this setup is that you could get a lighter quad than a ordinary
flat octo because you only have 4 arms,and it may get better lift capacity than a
coaxial x8 quad because the probs dont disturb each other that much like a coaxial x8.

The disadvantage would be (I think) to setup it correctly (maybe mixing with the pids' or
use angular motor mount as said before) or could it be someting else
And it may in some eyes dont look so nice
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Old Aug 14, 2011, 08:27 AM
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Actually, if you take the 4 arms/8 motors option, excluding motor coaxing, you have to compare:
- Each arm having 2 motors side by side, upside.
- Each arm having 1 motor upside, 1 motor downside (2 cases: upside motor tip & root of arm)
- Each arm having 2 motors side by side, downside.

As you are seeking for a specific advantage/gain, by comparing you can find the layout yielding the best outcome.
Perhaps the gain is noticeable, perhaps not; In this case, simplest is the best!
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Old Aug 14, 2011, 09:33 AM
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Actually, if you take the 4 arms/8 motors option, excluding motor coaxing, you have to compare:
- Each arm having 2 motors side by side, upside.
- Each arm having 1 motor upside, 1 motor downside (2 cases: upside motor tip & root of arm)
- Each arm having 2 motors side by side, downside.

As you are seeking for a specific advantage/gain, by comparing you can find the layout yielding the best outcome.
Perhaps the gain is noticeable, perhaps not; In this case, simplest is the best!
Haven't thougt about that... hmmm

Having 2 engines downside on each arm should be the best I think you should get best
thrust then props does'nt have to blow on the arm(maybe little to gain on) and then you
have less vibration(see the link in first post).

The disadvantage would be long arms to get place for the probs.Thats why
(I think) photoship have make their quad with one engine
up and one down
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