Here is the Image-Line manual on the Fruity Vocoder, and
here is a quick Fruity Vocoder tutorial on how to create a robotic-like sound in the voice you're trying to make sound like a robot. Other than that, you just need to play around with the oscillator, try out different waveforms and octaves and pitches until you get it right.
If this didn't help you, Glaze will probably role around here while I'm asleep, he'll be able to help you.
Assuming he's going to come here, since he's at every vocoding thread, lol