Servo horn spline indexing

[seaviper]

Recently on my F-104 90mm, I had one aileron horn that was not 90 deg at center. This caused asymetrical throw on that aileron.

I changed the horn to an identical one from another freewing servo. And it lined up perfectly.

Apparently the horns are not all indexed the same.

[OV10]

Did you actually compare the two horns? A horn is mass produced in molds by part numbers.
I would suspect an incorrect part number horn or I have also seen the same symptoms occur on the gear shaft of the servo too whereas the internal gearing wasn't set accurately.
An analogy is like if a mechanic has to change a serpentine(timing) belt on dual overhead cam motor and has one of the many gears off by a tooth, well the engine don't like that ;)

[seaviper]

The best i can figure is that there are an odd number of teeth on the servo output. When you flip the sevo over, as in an aileron application, then the indexing wont work. They must mold horns in two different indices.

i dont know. But my only other choice, since i am using the gyro, is to go in and move the gears a tooth over. But the other horn worked.

[seaviper]

Both servos center well and have the same movement.

[seaviper]

Just took off the horn to compare with others. No difference in markings.

I think that maybe when they cut the splines, the horn can rotate a little and cause the indexing to be off a spline or so. That's my theory