Nuts and bolts form the most entertaining aspect of "Robots," the new animated feature from the "Ice Age" folks. The story is set in an imagined world that's nothing more than a wildly inventive device, with slides, wheels, bells, drops, elevators, and a zillion other bells and whistles. Or, if you're old enough to remember a time before video games, you might think you're inside the world's greatest pinball machine, as characters zip from flippers to cushions, bouncing hither and yon, and zooming all over the table. Follow the bouncing ball, indeed.