Hi,
Is that you will develop one day a yaw damper. Some of our aircraft are sensitive and despite the autopilot should always monitor the ball. It would be probably not too complicated.
Electronically easy, mechanically complex. Attachment points, large forces and control friction conspire to make it aircraft-specific. A rudder with electric trim may be the easiest way, but adding mass to the rudder without careful analysis is risky.
I looked at this for Van's RVs, and the 'solution' involved a large horizontal bellcrank and spring attachment to the rudder cables, along with a powerful servo motor. The spring system introduces some interesting ciontrol dynamics but allows easy pilot override. Way too complicated for the benefit received for these particular aircraft.
Since there are dozens of different aircraft types, a custom engineered solution for each one is prohibitively expensive! The most common (RVs) really don't need it.
Just my experience.
Vern