I don't know, you could probably come up w/ a robot class for advancement, especially if you consider that machines can be programmed to learn. Your BAB would signify increased combat programming or acquired skill through learning (self-programming). Class feats could represent certain "upgrades" that the robot would have the processor bandwidth to control as it increased its level of learning. You might need some different classes for some basic types: Battle Driod, Protocol Droid, Astro-Droid (or whatever just using star wars examples). If you grouped the classes correctly, you could basically get away with only 3-4 types of robot (various trade-off's of BAB vs. skills & feats). Not all robots would be subject to such advancement. You'd have to have a certain TL of computer before it could truly learn and think at a level required for advancement.
I am wondering if there is going to be a T/Robotics skill. Does anyone know? For simplicity, many will say just use mechanical or electrical or computer programming as appropriate, but getting a robot to work with all 3 sets of systems (mechanical/electrical/computer prg) is pretty much a unique skill in and of itself.