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Setting up Multiple Servos

05/09/2005 by Don Szczur, Team JR

Copyright:© 2005 Horizon Hobby, Inc.

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Multiple Rudder Servos-In-Line
IMAC airplanes often have multiple rudder servos in line with a pull-pull cable setup, which provide a convenient and straightforward way of setting up a fuselage-mounted rudder control. Several people have asked me if the 8611 can be used to connect directly to the rudder cables. The 8611 servo has a very strong case and gear train and can handle the loads as shown in Figure 1. To set up multiple servos in line using a matchbox, start with the first (drive) servo. Plug in the first servo into a matchbox and move the arm 180 degrees to best configure it perpendicular to the servo. Turn on the receiver and move the matchbox dial to "1" and hit the "+" or "-" to precisely center the servo. Done! Rotate the selector clockwise back to "0" before turning off the receiver. Plug in servo #2, turn on the receiver and rotate the matchbox to "2". Use the same technique as above to set the center. Adjust the pushrods between the first and second servo for the proper length. Connect them to the drive servo (#1) but don't snap them into the ball links for servo #2 yet. Simply move the rudder stick to the left and then push the "+" or "-" buttons to match the servo end throws. Next, move the stick to the right and do the same. Done! Connect the servo arms to servo #2 and double-check the servos to make sure they are not "fighting" one another. I normally will fine-tune with a "+" or "-" at this time to remove any "buzzing" of the servos and achieve perfect servo throw matching. Again, be sure to rotate the selector all the way around back to "0" before turning off the receiver. Add a 3rd or 4th servo using the same technique as described above. I originally set up my TOC Extra with four 8411s and later changed the setup to three 8611s. This technique is quick and easy to do.

Multiple Rudder Servos- In the Tail with a 10X, without a Matchbox
If your plane requires multiple rudder servos in the tail, you can easily set up the servos using a matchbox as described above. But what if you do not have a matchbox handy? Here are a couple of techniques I used to set up four rudder servos on my 46% scale TOC Cap 232. I basically took the rear two servos and connected them as "rudder" using the mechanical linkage as a means to adjust their control throw for equal left and right deflection. If you have two receivers you can use a separate servo extension from each receiver to each servo. If you are only using one receiver, then use a Y harness. Then I took the front servo on the left side of the fuselage and set that one up as Gear (Channel 5) and the front servo on the right side of the fuselage as Aux 2 (Channel 7). I then adjusted the center and the end points using code 15 (Sub Trim) and Code 12 (travel) for each servo, so they match their respective rear-control surface drive servos as shown in Figure 2.

Multiple Elevator Servos- In the Tail with a 10X
The 10X has a built in "Dual Elevator" setup in to the wing- function (Code 22, Wing Type). Be sure to connect the right elevator in the ELEV port of the receiver and the left elevator in the Aux 3 (Channel 8) port. After mechanically adjusting the center, use Code 15 (Sub Trim) to fine-tune servo centering and use Code 12 (travel adjust) to adjust the end points for perfect throw on each elevator half. If adding a second elevator to each side (4 total), you can mechanically adjust the throw of each control arm by to match the control throw of each outboard servo. No spare matchboxes? If you use a matchbox for your rudder servos (per first section) you can set up the outboard elevator servos without a matchbox using a similar technique as was done in the multiple rudder servo section above using the Gear (Channel 5) and Aux 2 (Channel 7). A little-utilized feature that is very handy to correct loop tracking using dual elevators. Code 17 (Function Select) menu has an "alivator" trimmer for dual elevators, which allows you to adjust the elevator halves in opposite directions. This will correct any spiral tendency during inside or outside loops. Figure 3 shows the dual elevator setup on my Brio pattern aircraft. Although the 9303 transmitter does not have as many features as the 10X, setting up multiple elevator servos is fairly straightforward using the "mate" function. Simply "INH" the Aux 3 using the Device Select function, then "mate" Aux 3 to the elevator in the Wing Type menu. You can mate other servos easily using this same menu for multiple servos.