Bob assembled this mock up with a servo attached to a simulated control surface to show what happens to the control throw when you move the control rod to different hole positions. This is important for those using basic, non-computer-type RC transmitters.
A good starting point is to have the control rod connected to the outermost hole on the servo output arm.
An equally good starting point on the control horn end has the control rod placed in the outer most hole. This is explained in the text.
Q-28: Iíve noticed that the output arms of most RC servos have several holes and that the control horns located on the control surfaces also have a series of holes. Iím curious, which holes should I be using?
A-28: Most servo output arms will have three or four holes to accept the control rod linkage. Depending on which holes you select, you can be close to the center hub of the servo or you can be on the outer end. The same applies to the typical control horns that mount on your aircraftís control surfaces such as the rudder, elevator, and ailerons.
Depending on your choice of hole locations on both ends (servo end and horn end), you can obtain more or less control travel. If you are using a basic RC transmitter, this "hole selection" process can be quite important to you. My first suggestion when setting up a new aircraft is to go to the outer hole on the servo output arm. If you get an assortment of output arms, use the longer one at the start.
Go to the outer hole on the control horn end as well. In most cases this will provide an average amount of control and will likely start you in the ball park. If you are lucky enough to own a more advanced computer radio, this initial suggested setting may be all that you need. This is because your transmitter will have end-point-adjustment (EPA) capability on all the primary control channels. You can increase control throw up to 125% of the normal maximum and you can reduce the control practically down to zero or no control on the other end so your servo travel can be easily adjusted electronically.
Let's say you only have a basic RC transmitter and you donít have any special electronic control features. Your only recourse is to use the hole locations on both the servo output arm and the control horn. Start with the control rod placed in the outer hole of the servo arm and the control horn.
Power up your RC system and move the control stick while observing the control surface movement. If your control movement is too much and you want to reduce it, move the control rod on the servo output arm in closer to the center hub. Let the control rod remain in the outer hole of the control horn. As you get closer to the center hub of the servo output arm, your control throw will decrease.
What if your control movement is not enough and you need more? In this situation, keep the control rod in the outermost hole of the servo output arm but begin to move inside on the control horn, closer to the actual control surface. As you do this your control movement will increase. This is a simple concept, and once you get it set for a particular new model, you will likely not have to change it again in the life of that aircraft. Be patient during the initial set up and the results will be rewarding.