Besides the beloved Robot belonging to the crew of the Jupiter 2, we meet six other notable robots over the course of Lost in Space (although two are recycled and one has no dialogue that anyone but the Robot can understand).
In season one’s “The War of the Robots,” pace the title, Will rebuilds a robotOID. A robotoid is apparently a more advanced version of your typical run-of-the-mill robot. The Robot consistently refers to this creature as such throughout the episode, seemingly in order to underline a basic difference between a himself and the other (one suspects that, as far as the Robot is concerned, it is simply that robotoids are not to be trusted).
It is this same robotoid that appears in “Condemned of Space” in season three, except that in the later episode it is a robot warden. It never speaks, although it communicates with the Robot in some robotic language.
“The Ghost Planet,” season two, and “Deadliest of the Species,” season three, feature a female robot. Obviously not the same robot, or course—one has red make-up and the other blue… but they both probably came from the same page of the catalogue. Both are evil and not very well disposed to carbon-based life-forms.
“The Mechanical Men” presents a whole race of miniature versions of the Robot. They originate on the planet Industro where they are apparently the dominant life-form owing to their superiority over animal life. Obviously, this does not bode well for the Robinsons. Why robots on a planet we have never heard of should look like the Robinson’s Robot (or vice versa) is never explained. That fact that the Robot seems to be hiding some knowledge about the mechanical men from the Robinsons has been the source of some speculation.
“Hunter’s Moon” (season three) features a robot only in a supporting rôle; he doesn’t do much except compute odds and keep score. Perhaps owing to his rather limited skill-set, we next see him in “The Great Vegetable Rebellion,” where he reappears with a new paint job as a lawn sprinkler.
I guess when you get right down to it, there are actually only three guest robots in the series. Considering the number of androids the Robinsons ran into over three years in space, I guess that we have no choice but to suppose that robots are rather passé in intergalactic society (as a number of characters actually remark, most notably Dr. Smith).