[sanddrag]

I'm not sure of the exact equipment behind it but when I was young a local fire department had your exact idea at the local mall. It was a fire hydrant that drove around a small portion of the mall saying hi to all the kids. Someone was hiding away listening to what people would say to it and then he'd dpeak into a microphone and what he said would come out a speaker in the hydrant. It worked superbly. People were so mystified as to how it could hold a conversation with them.