Control surface linkage
Servo horn known: control horn length calculated.
H: offset of the control horn hole from the hinge axis, positive ahead (toward the servo), negative behind; B is then the hole height from the hinge. An offset hole creates differential, shown in the Result; the fix can then only be made on the servo horn.
Result
Build
Dimensioned drawing of each part, as a 3D model or a full-scale plan.
DifferentialDifferent up and down throws.Off
With 30 %, the small side is 70 % of the large one; F remains the target ▲ throw.
Radio setupRates and expo, allowing for the linkage.End points ▲ 93 % · ▼ 100 %Expo ▲ +4 % · ▼ +11 %
The linkage is not linear: it already acts like expo (▲ −4 % · ▼ −11 %, sharper around neutral). Radio expo adds to it: the "to set" values allow for this, for each rate and each direction.
In the radio, servo travel = D/R × end point. High rate: D/R at 100 %, the ▲ / ▼ end points carry the wanted angle and correct the difference between both directions.
Here, positive expo softens the centre. Some radios use the opposite sign: check at the stick that the centre does get softer. The two directions of the surface do not respond the same way: set one expo per direction.