A Fred Flintstone Version ;
Pushrod on top of wing , running aft . ( of all things ) . ( O.K. Pivot post in bushes - ' L ' arm over wing - pushrod pin )
Basic theory is the pushrod is horizontal .
A CROSS ARM at hinge . Rotateable . With a bush for each flap arm / horn .
As it proceeds , forward or aft , slides out the horn arm ( wire ) so is effectively further out .
Thus flap motion is quicker around neutral - slower as travel increases .
A bit of precision machineing would help , but brass tubes & wire would be a start .
A pushrod guide , and maybe a laterally split pushrod end , so it dosnt have any sideways motion may be best .
Maybe I can throw a sketch on .