This is going to result in quite a bit of nonlinearity. On the other hand, this is might be a good thing actually! You want more servo leverage at lower gears, when spring tension at its highest... I think a cam-shaped puley specifically designed for amount of cable pull your shifter has will work best. You, basically, need two separate designs - most shifter systems are either close to 2:1 like old shimanos, or 1:1 (sram, new shimanos).
Campa is inbeetween.
Using a small stepper motor plus a screw actuator like on x-shifter is the best setup actually - built in friction, more precize... but more complex.
Campa is inbeetween.
Using a small stepper motor plus a screw actuator like on x-shifter is the best setup actually - built in friction, more precize... but more complex.