How Do I Set Up My Servos?

By Bob Ackerman, Mid-Missouri Radio Control Association

One of the problems for most beginners is that they rarely set up the servos properly. I have said for years that you need to learn how to set up your aircraft mechanically before you touch the computer on your radio. Therefore, I am going to review what I do to set up any servo on my aircraft.

If I am going to re-set up an existing aircraft, first I copy the current settings to an unused memory location. See your radio manual for exact instructions. After the current settings are copied, clear all the programming for an unused memory location. Set all radio trims to the center. At this point the servo end points should be at 100% and the servo sub-trim should be zero.

With the control rod disconnected from the servo, move the control rod until the control surface is centered. Center the servo arm as close to center as possible. The servo arm should form a 90° angle between the arm and the control rod. Reposition the servo arm on the servo until you have it as close as possible, adjust the length of the control rod to match as necessary, and then adjust any sub-trim to center the servo.

Temporarily connect the control rod and look at all the links for that control. On a helicopter you may have two or three connections, as the control rods runs through bell cranks, before the servo actually connects to the control surface. Check each of these 90° connections and adjust as necessary. Now disconnect the control rod from the servo.

Now, turn on your radio and center the joystick for that channel. The servo arm should be in the center position. Move the joystick to one end of its movement and hold the joystick there. Manually move the control to where the servo arm is now positioned.

Notice the end of the control rod carefully. Does it move past the servo arm reach? Does it not move far enough? Make note of that difference then move the joystick to the opposite end and do it again. The difference between the servo arm and the control rod should be equal on both ends. If not, you may have something else not set properly.

If the control rod goes past the servo arm in both directions, then the control surface will move farther than the servo will allow. At this point, change the positioning of the control rod on the control horn closer to the control surface a hole or two. Reposition the control rod until you get everything matched up. Sometimes a longer servo arm is required.

If your servo arm moves farther than the control rod will move, then use an inner hole on the servo arm until you get everything matched up.

At this point, you have technically setup your servo. The servo is centered to the control surface and the control rod will move the control surface through its maximum range.

Now you can use your computer radio to adjust the end points for each servo to get the desired amount of control movement. Many times the control surface will move farther than recommended for normal, sport, or 3-D flight. Check your aircraft instructions for recommended control surface throws.

One warning: Helicopter pilots must ensure to check for any control binding during extreme joystick movements. The controls on some helicopters can move farther than necessary for normal flight, which can cause control binding during flight.