Daily News scientist-photographer W. Mangini on camp-stretcher beside the "Robot." All the switches mean something, and most are part of a modification called "PERC" (Photo-Electric Robot Control). This control faces the assumed direction of the flash, and when that occurs (day or night), the light is trapped by PERC, which sets off: (1) An alarm (made from an electrically agitated developer tin, and here visible on top of an ammunition box); (2) the "Robot" and its linked cine-camera, which wil