You should have seen the angry letters Cinefantastique magazine got late in 1977, accusing Lucas of ripping off everything from Lensman to Dune. Some also questioned what happened to that promising young man who made THX-1138. ;)
I could have sworn I read somewhere the robots in Silent Running were an influence on Artoo. He was originally going to walk in a fashion similar to a man walking on crutches, hence the third leg.
