Long servo arms or short control horns?
 

What is better for getting large amount of throw on a 3D plane, short control horns or long servo arms?

RE: Long servo arms or short control horns?
 

I like the longer servo arms. This lowers the axial force on the push rods - less likely to buckle. And less play in the system.

RE: Long servo arms or short control horns?
 

Longer arms on the servo move a longer distance at the end fartest from the shaft. Thus, if you hook the push rod at the end of the arm at the servo then use the inter most hole on the control surface you'll get the maximum movement.

RE: Long servo arms or short control horns?
 

I would never use inner holes on control horns for a 3D model other than a foamie.

Always use longer servo arms.

They are cheap and easily available. [link=http://estore.websitepros.com/1732294/-strse-4313/Dubro-Servo-Arms-Long/Detail.bok]Click here[/link]

RE: Long servo arms or short control horns?
 

I may have not been clear with my question.

I understand the physics involved. My question is based on the same amount of throw, one using a very long servo arm and shorter control horns and one using medium length servo arm and very short control horn. You would end up with the same amount of throw. I will give you an example of my problem, (these are random figures and I am not sure if they would even be accurate).

Lets say I need 2" of elevator throw,..... I could use a 2" servo arm with a 1" control horn and achieve my desired 2" of travel.... or .....I could use a 1" servo arm and 1/2" control horn and get the same 2" of travel.

Which way would you do it and why?

RE: Long servo arms or short control horns?
 

Blazer - I understood you the first time. you are correct in that it is the ratio of the two arms that determines the throw. to extend your example, you could use a 2-foot servo arm and a one-foot control horn. The advantage of the longer approach is that the axial forces are lower.

In your example, suppose you had a 1" servo arm and a 1/2" control horn and you measured the axial force in the connecting rod. Let's say it is 6 pounds of force. If you go to arms that are twice as long, then the force in the connecting push rod is only 3 pounds force. So the connecting rod does not have to be so stiff. Also suppose that there was 1/32 inch of play (slop) in the connection. With the longer arms, the 1/32 play will not cause as much deflection of the surface as compared to the short arms.

So longer is better than shorter. on a 35% scale aerobatic plane you typically see 1.5 inch or two inch servo arms, for example.

RE: Long servo arms or short control horns?
 

I would always use I could use a 2" servo arm with a 1" control horn WHY the load in the control rod is half and the slop at the control surface is half.

Use the shorter arms and horns you will get more slop and a greater chance of the control rod deforming.

bur here is the clincher YOU ARE MUCH MORE LIKELY TO GET FLUTTER WHICH IS AN AIRFRAME KILLER.

Longer [and stiffer] is better.