Downey, Jr., hasn't worn the "full" suit outside of a few select shots in the first Iron Man film.
I've read that it is even dangerous for him to wear the suit. In an Avengers intereview in EW, he has said if when he falls forward he has to tuck in his arms or he will break them if he doesn't.
The problem is that, at least in Iron Man 1, it shows that the suit is mostly CG. That film won't age that well.
I admit to rewatching IM on a borderline religous schedule, and that's kinda true, though it's more noticeable for the Mark III. The tip-off is the inconsistent lighting/color of the red parts of the suit between live-action and full-cg. In scenes where they added elements to RDJ they had to color match what was already filmed in the frame, which makes the CG invisible.
I'm almost certain that the Mark I was never
filmed in as a full-body costume because it's impossible to move like a superhero
in something that bulky without it actually being a powered suit. All of the scenes were the Mark I moves more than two feet is CG motion capture.
Robocop could get away with having something that chunky because Weller just had to be able to move
, and we're talking move as lawyers define the word.
Search for "The Visual Effects of Iron Man" on YT. It's really fascinating stuff.