I have two S3001 installed for my ailerons which are connected with a Y extension to my 127RDF receiver in Ch. 1. My transmitter is a 9CAP.
I get a different movement in each servo. Say in one of them I get a surface deflection of 1.5" up and 1.25" down. In the other servo I get 1.75" up and 1.5 down. It would seem that the up of the first match the down of the second BUT the other movement is completely out of synch within each servo and compared to the complentary movements.
I have used a new model in the transmitter and reset everything to be sure I started with a clean slate before attempting anything. Also, I made sure all the servos where centered.
I have checked the mounting of the servo arm in the splines, the mounting holes of the pushrods in the servo arms and the control horns. They are the same.
If I reverse the connection of the servos in the Y connector then I get the same servo acting disproportionately in the other direction.
I was able to minimize the difference in movements by setting a EPA of 50% in that channel, just for the sake of testing...
Any ideas? I would prefer not to have to mount the servos with a mix (say Ch. 1 and 6) and mess with the mix settings.
Thank you
PS: Is there a stop in one of the gears that prevent the servo from moving further or the movement in either direction is just controled by the pot?

You don't say what airplane your servos are mounted into, but if you have large control surfaces, what you've found is normal. Very likely, the servos, themselves are very close in how far they move. That small difference, though, is exaggerated by the trailing edge of a large control surface.

The variance is because no two servos will have exactly the same amount of movement. That's due to variances components in the servo. The actual movement of the two servos will be close, though. You'll need to adjust the positions of the linkage on the servo horns and control horns to get exactly-equal movement.

Another way to get perfect synchronization would be to us a Futaba MSA-10 Servo Synchronizer. This allows you to get centering and endpoints exactly matched between up to four servos on a single channel.

Thank you Bax... True, large control surfaces so the differences must be exgerated...
Adjusting the position of the linkages will be harder than doing a mix and adjusting from the radio.
Mix! Here I come!
However, it doesn't explain the difference in movement in the same servo...

If a single servo has differences in throws when you change it to a different control surface, then you have to take a good, hard look at the geometry of the servo position, servo arm position, control surface hinge line location, and control horn on the control surface. If the two control surfaces are not exact (and we mean EXACT!) mirror images, then you'll get differences in throws due to differences in geometry, and that will be exaggerated by large control surfaces.