I have one called The Vocalist by Digitech. Very old school legacy type piece of equipment. There's really nothing specifically built for the "robot" sound I think you mean. I have 50 presets in mine. Male, female, 2 part, 3 part, different chord voicings.... It has a MIDI in and a MIC in. You plug in the mic, you plug in the MIDI, set the keyboard and device to the same MIDI channel, and yoru mouth becoems the trigger for the keys. You can press keys all you like but nothing will come out of the vocoder until you say something into the mic. You CAN make it sound like that, but I don't choose to use it that way.

The newer schools units just kind of follow along as you go. Similar in concept but newer technology.