Right you had a question. Section 102b makes it clear that copyright doesn't protect ideas. It's another way of saying that copyright only protects the way you express an idea, not the underlying concept. The principle has been applied to characters in fiction so for example, the idea of using a character who is an anti-social computer hacker is not protectible. But the character would be protected if it's a pierced female hacker who weighs 100 pounds, has a dragon tattoo on her back, likes death metal, shops at Ikea and (spoiler alert) has a creepy Russian gangster father with a burned off face. In other words, it all depends on the degree of expression. The same is true for the design (or appearance) of robots that are characters in films. You are correct that the idea of a robot is not protectible ... but the appearance of a robot like R2-D2, Robbie, C-3PO or Klaatu (or any other famous movie robot), is probably protectible under copyright. In some ways, one could even argue that a uniquely designed robot is not that much different than a well-crafted sculpture or other three-dimensional artwork.
So, are robots protected or not? Determining whether a robot has enough expression to be protected is a matter sorted out by courts, a factor which would place you at a disadvantage (since you probably can't afford litigation - who can?). Also, to make things even more confusing, the appearance can be protected under trademark and related laws. (What you're doing is not much different than making an audioanimatronic version of a fictional character.)
What about reverse engineering? Reverse engineering wouldn't have much to do with your situation. First, you're not reverse engineering the robot (because the movie robot apparently doesn't function for real) and second, reverse engineering is primarily a defense used in trade secret disputes.
Bottom Line Dept. Best of luck acquiring rights. No need to wonder about what rights to ask for ... if the studio wants to go ahead with it, they'll tell you what rights you can have. By the way, it appears as if the film Metropolis is in the public domain, so there's one robot that's freely available for exploitation.