While Robby the Robot from "Forbidden Planet" appeared in an episode of "Lost in Space", the Jupiter 2's robot, "B-9", is a different model entirely. B-9 was designed by the prop builder who designed Robby, Robert Kinoshita, but Irwin Allen hired Kinoshita to come up with a similar design that was not as costly to build.

Here's a site with lots of info on B-9: http://www.aboyd.com/robots/lis.html

Compare with one of Robby's many sites: http://www.the-robotman.com/nv_fs.html