When I did my rudder trim bungee I settled for the KISS manual principle with a sort of jack screw setup. Teleflex cable and a threaded wheel that moves the inner cable in or out with the distance from one turn being the thread pitch. Works a treat for the required movement. Could have fitted a trim servo and switch but settled for the simple and practical manual turn method. The cables come in 1, 2 or 3 inch movement.