Dark Trooper 1 is just a prototype of the skeleton, perhaps with some protective sheets to test some material.
Dark Trooper 2 is in fact the finished deadly weapon.
Dark Trooper 3 is made of the Dart Trooper 2 Hull using an air-pump :D
For those who can't figure what I mean, I recommend you watch the CG animation Pump Action (
http://pocketmovies.net/detail_83.html) :p )