Think R2's kind of a mix between remote control and a small actor since day one. Think a lot of what Kenny did was honestly a lot of moving the 'suit' when he was in place and had to rotate and nod, but the rest was done by remote (although harder to control in those days) when R2 was moving around. Isn't as easy as it sounds, imagine being in the Tunisia desert in that thing (Same goes for Anthony Daniels and 3PO) and remote control used to be hell on film sets with all the other signals going around.
One of the Mythbusters, Adam Savage I think was very involved with the R2 stuff for the prequels I think.