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Gaining More Control
In Part
1, we discussed uses for sub-trim and adjusting the ATV
or endpoint travel volume to optimize your linkages.
Remember the key to what we want to accomplish: Servo
resolution!
We often
spend lots of money on TX’s and servos, yet many of us set
the dual rates at 40%. Just because your ATV is up over
100% doesn’t mean that it's okay to set your D/R at 40%.
You're giving up resolution on the servos.
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Troy
Newman w/Supreme |
Today's
servos are very fast, so we don’t need to optimize the
linkage for speed. We need precision linkages and servos.
Centering is only part of the equation but precisions
throughout the servo's travel will help all aspects. If
you're using less than 80% on your flying rates (whether
that's D/R or not) then you're not using the radio or the
servo to maximum resolution. If you're not using a rate
above 80% for specific purposes in the pattern then you need
to get longer control horns on the surface and/or smaller
(as in shorter) servo wheels or arms.
We also
want "square" linkages—meaning the servo is at its neutral
point when the pushrod is 90° to the servo arm (as
shown in the drawings in Linkages Part 1). In Part
1, we use sub trim to set the servo arm in the right
location and then we mechanically adjust the length of the
pushrods to center the control surface. This is setting the
pushrod connection point at a right angle (90°) to the
servo's rotation. This gives symmetry to the servos travel
and prevents building differential into the linkage.
Rudder
Since we
most likely use pull-pull on rudders, let's discuss some
problems commonly seen with rudder linkages. Too often, the
control horn on the rudder isn't positioned right. The pivot
point of the clevis on the rudder needs to be over the hinge
line. If it isn't, there are several things you can do.
Adjusting
the Pivot Point
Option 1
A 6-32 bolt can be bent forward on both sides to get the
pivot point over the hinge line.
Option 2
You can use an offset style control horn to locate the pivot
over the hinge line.
Option 3
If you don’t set the pivot point over the hinge line at the
rudder, then you'll need to offset the connection points at
the servo—back in the direction of the rudder in order to
compensate. It'll need to match the distance you're off at
the rudder.
Any of the
above will work.
Next: Pivot Point
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