Duel servo elevator ???
 

Question...my plans show connection between elevator halves and I want to have a servo for each half...can I do both?
can I use 2 servos and still have connection???
​i do have new transmitter with all the latest goodies

Yes you can provided your servos are in sync. If not they will draw quite a bit more power and if digital servos they can get hot and eventually fail. That being said, adjust them as you would any other dual elevator setup. The question however is why do you feel you need both?

If you go dual servo I wouldn't connect the halves

+1......Besides strength in torque, the reason for seperate servos for each flight control is for finer adjustments for aerobatics. Gluing the two elevators with the “U” bar, most don’t get them glued in even. Thus one elevator is a degree or two off from the other. This causes corkscrewing through loops, Immelmanns, Split-S, etc.

Thanks for input people.
plane is big robin hood 99 and I wonder if 1 servo is enough?
I have questions about servo strength required. ....
If anyone can steer me in correct direction......how do u determine hardware and servo strength when no info given?
I see pictures of big planes with chincy looking nylon horns and others with HD control horns ....very few old plans show torque for servo?

BadAngle,

Here is a build forum that might help.

IMHO.....One servo for the elevator is enough. Just get the “U” as even as possible in each elevator half. A Hitec 5645MG or Hitec 5625MG. Those are common servos for that style of plane. Mount the servo in the cabin. I would recommend fiberglass or carbon fiber pushrods. Old school is using wood dowls.

https://www.giantscalenews.com/threa...d-99-kit.9898/

Thanks rcflyerdan.....I built mine just like the one in the link u sent.....page 20...post #196
I have checked out all the build post on the plane and I was hoping to have option of
1 servo or 2 ......gives me balance options....as far as mounting in cabin always an option.

I got kit when I had 77cc glow radial but never felt comfy with the engines performance so I sold it.
I MIGHT someday get the gas version for this plane and I know how heavy the radials are.
So now I want to fly with 40cc gas twin with option of changing to engine 2x the weight in the future.

Looks ok, as long as the elevator doesn’t have the “U” glued into the elevator. The elevator with the U now becomes one flight surface. The issues using two servos on one flight surface becomes matching them up. The closer that all geometry is in the set up, the easier it is to match them in the transmitter using two channels. Where the servos are mounted depends upon what engine that you are going to use. Think of balancing the airplane as a tettertodder. Whatever is 12 inches towards the tail. It takes double the weight at 6 inches towards the engine. Each metal gear servo usually weigh about 1.5oz . As far as carrying the weight, the airplane will have no issues provided enough power.

Part of the idea of two servos is that they each push the one side. On a precision pattern model this is important because you can ensure the surfaces are matched exactly. On a Robin Hood this isn't as big a deal.

A side benefit of dual elevator servos is that if one should fail the other will at least give you enough control to land.

But if you link the two sides the one servo might not be able to fight the other. Not to mention that if the servo motions and pushrod geometries are not identical in all ways that the two sides might not track identically until you get things all matched with some programmed tweaks in the Tx. And if that happens the servos will fight each other and draw large amounts of current. And with the link forcing the servos to fight each other it becomes hard to know which one needs to be tweaked to match the other.

So dual servos = no link. One servo = link. Using the two methods at the same time is just a bad idea.

How much power do we need for the surface to move? There used to be a number of online servo torque calculators. But now there appears to be only one that I can find. HERE IT IS. When you enter the maximum speed use a figure for what you expect it would be as you exit a longer dive done at full throttle. Something like a Robin Hood isn't going to get going all that fast. The calculator is in metric so I'm calling it 120 kph which is roughly 70mph. And I think that's being fairly generous. I don't have the plans for the 99 but looking at the small Robin Hood .10 off Outerzone and scaling up to around 100 inch span the total elevator span looks to be 30" or 75cm with a 3.5" or 9cm chord. You'll have to measure and amend that. And with an elevator that large it'll only need about 15° throw each side of neutral for lots of control. But for sake of discussion let's call it 20° which on that wide would be lots. And finally most of our servos move a bit more than 45 to each side so I used the 55 option to match to the fairly common 110° full servo travel at 100% programming of the Tx. Plugging all that into the calculator I get 31.4 inch ounces to move the surface against the air flow.

Note that this does not include any mechanical drag like pushrod connections or springiness or drag in hinges. It is only airflow. Plus we don't want to run the servos at anywhere near their max as that draws excess current due to loading the motors. So I like the idea of doubling the 31.4 inch ounce result and use a servo with 65 in-oz torque rating or more to use one to move the whole thing. Obviously you could divide that in half if you opt for dual servos.

Thanks for all the good information. ..
I think I will disconnect connection between elevators and go with 2 servos.

this is an old thread, but it addresses my question., but on a totally different crate...

I would like to try dual-servo/split elevator on a 72" RC Buzzard Bombshell for OS FS 56a now on the slab. and use the split elevator with some kind of custom elevon mixing, since Bombshells got no ailerons. It would become a 4-channel airplane instead of 3, at that point.
I know this mod is not needed with such a stable free-flight type design, but it would allow reduced poly/dihedral for a slightly more realistic look as well as allowing the also un-needed AS3x, if desired. On such a lightly loaded and clowny aircraft, a single push-pull micro-servo should be strong enough for each elevator surface, wouldn't it? Perhaps climbing to new heights in creative absurdity?