Great Planes Matt Chapman Eagle 580 ARF 1/3 Scale - GPMA1286 - Manual (Page 25)

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When connecting pushrods
and setting up your control
throws, it is
critically
important to use proper
pushrod geometry — that
is the distance from the
pushrod on the servo arm to the center of the output shaft (
servo arm offset) compared to the distance from the pushrod
on the control horn to the pivot point ( control horn offset) .
Pivot point
CONTROL
HORN OFFSET
SERVO ARM
OFFSET
Note: Your control horn may vary.
One particularly dangerous situation arises
when the pushrod on the servo arm is too
“far out” and the pushrod on the control
horn is too “close in .” This setup is usually
chosen by pilots who are trying to achieve
maximum, “monster” control throws for 3D
flight . But with your pushrods set up this way, any free play (slop) in the linkages or servo will be greatly magnified, possibly
causing destructive control surface flutter . Additionally, if you have to turn your ATVs way down for “normal” throw, the result
will be poor resolution and poor servo holding/centering capabilities . More importantly, too much force may be transmitted
back to the servo, possibly causing control surface blowback, stripped servo gears or stripped servo arms—the latter two
likely causing a crash .
POTENTIALLY DANGEROUS
PUSHROD HOOKUP
Pushrod far out
on the servo arm…
Long
distance
Short
distance
…pushrod close in
on the control horn.
Here is an optimum pushrod setup—the
pushrod is “close in” on the servo arm and
“far out” on the control horn . This situation
gives the greatest mechanical advantage
of the servo over the control surface which
will increase the servo’s centering capabilities and output torque, minimize any free play in the system and allow high ATV
settings for optimum servo resolution and positive control “feel .”
Note: When the pushrod is “close in” on the servo arm,
make certain the servo arm can travel through its full range of movement without the pushrod (or clevis or other type of
connector) interfering with the servo arm, output shaft or servo case .
PREFERRED
PUSHROD HOOKUP
“Closest in”
on servo arm “Farthest out”
on control horn
If the optimum situation doesn’t provide
enough control throw, the pushrod may be
moved inward on the control horn, but it’s
better to go
farther out on the servo arm
because this will introduce less free play
than the alternative . Only after moving the pushrod all the way out on the servo arm, if you still can’t get the throw required, you’ll
have to resort to moving the pushrod closer in on the control horn .
Note: If you have a computer radio, it is always desirable to
set your ATVs to 100% (or as near 100% as possible to achieve the control throw required) . If setting up a model that requires
extraordinary control surface throw (for 3D flying for example), start by “maxing-out” your ATVs (typically 130% – 140%) . Then,
the dual rates in your “normal” flight mode will still be acceptably high (70% – 80%) for good servo resolution .
ACCEPTABLE
PUSHROD HOOKUP
Move the pushrod farther out
on the servo arm…
…But leave the pushrod in the farthest out
location on the control horn.
Proper Pushrod Hookup
Avoiding Flutter, Maximizing Servo Output Torque