I quote myself now from wayyy back.

I do have a problem with Luke levitating Threepio being enough to scare the little buggers into letting our heroes go. For years now the Ewoks would have seen a strange moon growing in their sky, plastic men flying on metal bikes and firing lightning out their hands (laser guns not Sith magic), so would they be so scared of some golden boob floating around on a chair? Couldn't Luke pull off a more effective light show and spare us Threepio acting like Dr Smith in "Lost In Space"?

I've been thinking about what can be done here, couldn't Luke get R2 to project a hologram over Threepio of some alarming creature, the floating chair isn't enough, what with what the Ewoks had been seeing on their world around that time.