Servo linkage geometry... for 21 and older
This thread is to help you guys out that are new to setting up proper linkage geometry on a giant scale plane with surface mounted servos with "bolt and clevis" style control horns and adjustable Titanium linkage rods.
Make some paper protractors.....and chug a cold beer (shot gun...no wimpy stuff) Punch a hole in the bottom , pop the tab ,and down the hatch! *Roaring belch with some residual projectile foam.* After this The wife will always poke her head in the garage to confirm how much of a HOG you are. Hog it up my man ...just hog ....it....up.
Make sure the center point of the protractor is directly lined up to the center of the servo spline screw hole. You will need to measure and cut the paper protractor to do this.I use a calipers to be exact.
Say you want 5'' of throw on ailerons.
Measure 5" at the aileron throw and hold it while you look at the servo to mark the location of the arm on the protractor.(it helps to have some one hold it)....while you shot gun another beer.
You can also take a piece of thin cardboard inside the root of the aileron and make marks on it at 5'' aileron throw. This will keep you from having to fiddle with the tape measure.
Then adjust the titanium link to achieve the same amount of servo throw each way at the servo arm.
I usually end up with 53 degrees servo arm throw each way from center as the aileron moves 50 degrees each way from center. After my linkages are adjusted the servo arm ends up being about 12 degrees off from 90 degrees toward the aileron. This is because when using bolt and clevis style control horns the pivot point of the clevis is not centered directly over the hinge line. Thats why you have the off set at the servo arm center when you finish adjusting.
You are going to keep measuring 5'' aileron throw ,hold it and mark the protractor at the servo arm each way. ( every time you adjust the linkage rod, center the aileron , hold it ,and mark the protractor center... chug a beer ).
Tip1: lets say you find out the servo arm is traveling 40 degrees from the center mark one way and 65 degrees the other as you hold the aileron at 5'' each way. (If you can remember this it will save you lots of time.)
1)Hold the aileron at center ..(tape works)
2)turn the titanium linkage rod so it draws the servo arm toward the direction direction of the smallest amount of degrees of servo arm throw..about a full turn on the linkage rod will is a good start if its way off like above 40/65. I call this "giving to the smaller or lesser number"
Tip2: Titanium linkage rods have right threads on one end and and left threads on the other to allow for adjusting with out un hooking the ball link. I always install the rod so the right threads are on the servo end. This way I know what direction to turn the link to shorten or lengthen it .
Tip3: on the first servo..Say you ended up with 50 degrees aileron throw each way as the servo arm moves 53 degrees each way. Make sher all other aileron servos have exactly 53 degrees too at 5'' aileron throw. On the other servos....Once you get the control horn clevis hight close by measuring off the hinge ...You may need to adjust the control horn clevis on the other servos up for more servo arm throw or down for less servo arm throw to get that 53 degrees each way. In other words...You don't want 51 degrees each way on one aileron servo and 53 each way on the other.Equal throw is good but it also needs to be the same amount of servo arm throw on all the servos for the ailerons as you hold the aileron at 5'' from center.
Treat the elevators the same.
A rudder tray is a different animal but the same concept....shot gunning a beer after each adjustment.
Last edited by Buttface; 03-03-2011 at 09:40 AM.
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120'' Extra 330LX build and review
does it matter if I use a plastic arm instead of a metal arm. How do you hold the 7950 servo still long enough to measure the linkage. Help me out teach.
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