5 Servo Setup Tips

Nov 06, 2012 2 Comments by

After installing your servos according the manufacturer’s directions, you might find that when the servo arm is placed on the spline, it isn’t at a perfect right angle to the servo casing. Or, after you’ve hooked up the various linkages, you discover there is too much or not enough travel throw when a certain control surface is deflected. How about adjusting those throttle linkages to get that carburetor barrel either wide open or fully closed when the throttle trim is lowered? This article will help you to achieve basic radio- and servo-setup success.
1 First, check that your servos are properly installed. Unless you’re flying a foamie or small electric in which the servos are glued into place, use the rubber grommets and brass eyelets that come with your servos. Install them so the wide brim of the eyelets are under the grommets (between them and the servo tray). Tighten the screws until their heads meet the brass bushing’s top edge. The rubber grommet will be compressed a bit, but that’s OK. The object is to have a secure, shock-mounted servo installation that won’t move when the servo arm is deflected. If the eyelet is installed with the wide end up, the grommets will be compressed so much that they won’t isolate the servo from the source of vibration.

  
2 This is a crucial setup check and should be done before any linkages are hooked up. Does the control surface move in the correct direction relative to the transmitter’s stick input? Start with one servo and place the servo arm on the spline. Don’t concern yourself with whether it is exactly 90 degrees to the case. Turn on your transmitter and receiver and move the stick (top) that corresponds with that channel. If you see that the arm is moving in the wrong direction required for the correct control surface movement (middle), use the servo reversing menu and hit select “norm” to “rev” so the servo responds in the correct direction (bottom). Now go one by one through the remaining servos and correct their directions if necessary.

   
3 First, all servos should be centered with the transmitter sticks and the control trim levers centered, then place the servo arm on the spline (mechanical portion). Move the arm’s position on the spline to get it as close to 90 degrees to the servo case as possible then, if necessary, use the sub-trim menu to adjust the arm’s position. Do the mechanical adjustments first; don’t rely on the subtrim function only. This can affect the servo’s overall control throws and end points.
For most elevator, rudder and aileron servos, the servo arm should be at a 90-degree angle to the case.


4 Because the servo placement is usually pre-determined in an ARF, you need to mechanically (i.e. no programming) set the control linkage at 90 degrees to the servo arm. Determining which hole to use in the servo arm is simple: if you want more throw on the control linkage, place it in the hole farthest from the servo’s center; closer if less throw is desired. Different size models will have various linkage setup requirements, so consult the instruction manual for the proper linkage setup. With the linkage disconnected to the servo’s arm, there shouldn’t be any binding when you move it by hand.

  
5 The control surface’s linkage connection depends on the type and size model you’re flying. If you want to achieve maximum surface deflection, connect the clevis to the control horn using the hole closest to the surface. For large-scale and 3D airplanes, connect the linkage to the outermost hole (farthest from the surface) for maximum leverage; this also helps to prevent flutter. This photo (below left) shows threaded rods for control horns with plastic connectors to which the clevises attach. Note that they are at the end of the rod rather than close to the surface. It is usually best to have a straight line from the pushrod linkage’s fuselage exit to the hole in the surface’s control arm/horn. Sometimes a slight bend in the rod (top right) after it exits the fuselage is needed to relieve servo and linkage binding.

  

Stay tuned for more servo setup tips in next week’s newsletter!

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About the author

West Coast senior editor About me: I’ve been involved with RC aircraft since high school and have flown just about everything. I started my RC career with scratch-building, but now like many pilots I rely on ARFs to get me in the air. My main focus is on pylon racing, aerobats, combat and scale warbirds.

2 Responses to “5 Servo Setup Tips”

  1. Anonymous says:

    great instruction, very easy to understand and implement.
    Thanks.
    Steve

  2. Roland A. Brawner says:

    After setting up the pull-pull connections to the rudder of my Ibis 120, it looked quite similar to the last picture in your article. My problem (and yours, as well, from the looks of the picture) is that the elevator is going to interfere with the rudder horn. As mine was pull-pull, I had the issue on both sides. I have slightly less elevator area now, but, the rudder and elevators don’t interfere!
    Yours might work okay as is if you always applied full right rudder any time you had to work the elevators…..might make landings a little tricky!!

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