Lockhart said because it wasn't easy to get in and out of the suit, Mr. May kept it on during breaks.
"He was a smoker," she said. "From time to time (when he was on a break), we'd see smoke coming out of the robot. That always amused us."
http://www.boston.com/bostonglobe/obituaries/articles/2009/01/19/bob_may_69_was_the_robot_in_lost_in_space/Here is photo of Dick Tufeld who was the voice of the robot:
And a remarkable anecdote of his:
http://www.promisedplanet.com/DickTufeldMiracle.htmThe original cast of ''Lost in Space'' included, clockwise from back row, Bob May;
Bill Mumy; Mark Goddard; Jonathan Harris; Angela Cartwright; Marta Kristen; and
June Lockhart. (Steven Senne/Associated Press/File 1995)
PS: I loved Bill Mumy (Will Robinson) in Babylon 5.