There were a total of three "Voltrons": Voltron I of the Near Universe was the "Vehicle Force", and the "Lion Force" of the Far Universe was Voltron III. Voltron II, from the Middle Universe, featured three humanoid robots that combined into one multi-armed fighter; this version was never shown in the US (though toys based on this show were released).
The first season of Voltron was not a straight dub from the Japanese anime series Hyakujû-ô Goraion (neither was the second from Kikô Kantai dairugger XV) due to American broadcast standards - "living" beings were never killed on-screen; mechanical creatures, however, were fair game. One of the most noticeable differences involves the character Sven. In the Japanese version, this character died after battling the enemy's witch after six appearances. In the American version, he was seriously injured and left to heal, and returns near the end of the season. In the Japanese version, this was his brother at the end of the series. The third season (second season for the Lion Voltron Force) was created specifically for the American audience.
Pidge, who was a member of the Lion Voltron Force, had a brother named Chip, who was part of the Vehicle Voltron Force. However, the two Japanese inspirations for the show, Hyakujû-ô Goraion and Kikô Kantai dairugger XV are not related, up to and including these characters. This is also why the antagonists in both series were known as belonging to one race, the Drules, in the American version; while "Kikô Kantai dairugger XV encountered them only after they began a planet search, the Vehicle Voltron Force were always watching out for them (and the Far Universe inhabitants were mentioned as being a part of their empire in the first season).