Jim,
You are absolutely right about the Robart hinge installation...I think you will be very happy with your improved setup. You stated earlier that your rudder was 66 grams, I'm curious what your final mass will be after your mods. My main concern with the Impact stock rudder is that there is quite a bit of mass aft of the hinge line. From a flutter point of view, as you know, you'd like to keep most of the rudder mass close to the hinge line....you probably don't want to add more weight to the hinge post area (or add weight to the counter balance to statically balance the rudder...things will indeed get heavy in a hurry).

Originally, I was going to do just what you (and others) have done, but in the end decided to make a completely new all built-up rudder. However, I think that by eliminating the awkward/sloppy Robart hinge installation you have cured most of the problems. Keep us informed of your progress. Maybe I missed it in your earlier posts but are you going Electric or Glow with your Impact? If glow, what engine? I'm still undecided about whether to use my 140 Dingo or 140 RX

-Erik