Based on the script, A. Arnold Gillespie, the chief of special effects for Forbidden Planet, came up with the design that everyone liked, according to Arthur Lonergan, after he and Lonergan had sketched and discarded numerous ideas. Gillespie based his design on the shape of the old-fashioned pot-bellied stove. Lonergan turned over Gillespie’s rough design sketches to production illustrator Mentor Huebner, who refined the aesthetic look of the robot (Huebner claims that Robby was his design). "I designed about fifteen of them, and they finally lit on one that was used," he said. Huebner also mentioned that Gillespie’s early Robby sketch as a refinement of Huebner’s concept. Lonergan, however, remembers that Gillespie originated the idea, and points out the Huebner would refine Gillespie’s ideas, not the other way around. Huebner abandoned Gillespie’s slip cast rubber legs, similar in design and operation to the arms, and hit upon the jointed ball configuration for the robot’s legs. "I thought of having a very short man inside, being able to look out of the stomach, and then have a false head built on him which brings him up to average height," said Huebner. Gillespie’s concept had the operator’s head inside the robot’s clear plastic dome. Huebner’s changes didn’t alter Gillespie’s basic design, but resulted in the clean lines and well-proportioned appearance that makes Robby so popular and pleasing to the eye.
By the end of 1954, the art director, Arthur Lonergan turned Huebner’s work over to Robert Kinoshita, head draftsman of the art department, who would produce the working drawings and blueprints for Robby’s construction under Gillespie’s supervision. With his miniature scale model of Robby approved, Kinoshita began drafting the plans from which the robot would be constructed. Kinoshita’s working drawings were turned over to Jack Gaylord, head of MGM’s Prop Shop, who was in charge of the molding and assembly of Robby’s plastic parts.
There were 3 units made for the movie, and those 3 were sold to different people. I worked with the guys who owned one of the originals (and they claimed that their original was the only one with original working electronics), and they appeared with it on an episode of Love Boat (the episode was called "Programmed for Love" and was cheesy as every other episode of LB). One of the owners claims to have "the one and only" original and tends to sue folks who own the other 2 originals as well as folks who have built replicas. The waist is extremely narrow and I seem to remember that no one with a waist larger than 28 or 30 inches could fit in the suit.