Thanks for the kudos..

BUT, you can't make a statement like you did and just let it hang out there...

So what's the "easier" solution?

:-)

"Easier"????
Put the servo arms pointing in the same direction.
Use a y-harness with a reverser.
It can't get easier than that!

Place the servos almost anywhere in the airplane that you want in almost any orientation that looks halfway close to sensible.

Use nyrod for the connections.

How hard is that?

Only requirement is that you have a 90degree connection at the servo arms and a 90degree connection at the horns.

The only requirement for what result?

Apparantly - a rather small deflection setup is all that is being addressed
try this with your setup:
swing the elevators thru 45 degrees each way - and allow only a degree of error
the simple reversing setups and any mismatch in geometry will typically show large errors. a 15 degree throw setup is far easier to do

.
No.
The servo arms -MUST- be pointing in the same direction to get the -SAME- deflection at the surface..
Screwing around with the other stuff is like doing this to change a light bulb..

Right on Paul.

Just to clarify a point that others may be unclear on:

Regardless of servo arm orientation relative to its respective elevator horn, if the geometry is mirrored across the fuselage longitudinal axis, both elevators will match each other (this is intuitive), HOWEVER, a consideration that is less well understood is:

If the servo arms are not pointing the same direction as, and parallel with, their respective elevator horns, elevator deflections will not be symmetrical up and down, unless servo endpoints are unequal, which will result in different times required to reach a given deflection, since the servo will have to rotate farther one direction than the other. In fact, for perfect up/down symmetry, both the servo arm and elevator horn must be the same length and be square with the arm/horn. The small amount of asymmetry that results from unequal arm/horn lengths is acceptably corrected with endpoint adjustment, since it is often necessary for desired throws.

Having one pointing up and the other down would be unacceptable to me for anything other than a trainer.

Paul, one question: In your drawing that I have re-posted here, it appears that the "right" servo arm is shorter than the "left". Was that intentional?

Just a routine engineering ......... up!
Reworked at 10x to get some meaningful points to work with..
.
I have an example of dual elevator servos with the arms pointing 180 out... This plane began life as a rudder-vator glider. Two servos, glued to the sides.
I changed it to ailerons and elevator, and wanted to use the two rudder-elevator servos as the elevator servos.
Not wanting to pry one loose, I used a servo reversing y-harness to get equal elevator motion from the two.
As pointed out in the first drawing I posted, with the two servos mounted with the arms rotating in the horizontal plane, and the surface horns rotating in the vertical plane, the orientation of the servo arms isn't important.. both can point in the same direction, or opposite each other.

I want to thank everyone who contributed to this thread and was kind enough to assist me in my resolution to the dual elevator servo question!

After careful consideration, examining and evaluating all the excellent advice and suggestions, I arrived at the only possible solution that my math and analytical mind could grasp...


I bought an EXPERT servo reverser Y harness and am done with it!

For 6 bux, it took all the guesswork, mounting issues and geometry OUT of my equation! :-)

Thanks again guys!

Pointmagu

ok you guys, youve been making me think!!! like i heard , im getting a corner headache!!!

my edge has the elev serv's mounted up against the stab, thats bottom of stab. they are staggered, front /back, thats one is closer to the elevator.
cause the fus. is not wide enough to mount em equee distant from the elev horn. pushrods are dif. lengths. (dumb design , if ya ask me!)

rod with 90 deg. at arm and horn, i dont get very much throw. (rod in 1st arm hole, not 4th hole , which is desired)
the throw is the same both sides but not enough for 3D.
from what you tell me this throw will be linear to both sides. thats good!

my question: will making the rod like my image (with S bend ) give me more AND linier motion of elev.????
(the arm side in the 4th or 5th hole, and the rod at horn the same as before )

OR is the angle of throw still not 90deg. just because the distance from elev to rod and serv shaft to rod are dif.???

pardon my drawing and pardon my wisdom!!

thanks guys!!!


gotta say you guys have really helped me on this subject... THANKS to all of you!!!

No s-bend in the pushrod!
Accept the slight angle from the servo arm hole to the elevator horn hole.
The effect of this will be a difference in the total elevator travel, up to down.
Both sides will move the same amount relative to each other in the same direction

hi paul,

the prob. is the angles are not equal on both sides..
the rods are dif. lengths due to the staggered mounting of servo's..
if the serv's were back to back then the angles would be fine, giving a small differencial, which would be ok

i may just put up with it or re mount one servo , so there back to back... pain but maybe worth it..

ill see how the lesser surface deflection is..when i go on the madien flight..

thanks for your help!!!
b

S-bend will make no difference in surface throw compared to a straight rod, unless you are trying to avoid binding with a clevis or something, i.e. there is no benefit.

Anything other than a straight rod from servo to surface in a high-loading situation can create a potential for the bent rod to bend more under the load.
At full surface deflection the manuvers will be extreme enough that any minor differences in deflection can be removed by the other controls.
It's only in precision flight that getting the controls exactly identical that it really matters.. 3D stuff is so full of couplings and crossed controls precision in surface position isn't that big a deal.