From the rules:
7. Materials This rule is not just about the robot... This rule controls everything you bring from the pit area to the competition area including the robot, all attachments, and all strategic objects when viewed all at once as a package. All these objects must be made entirely of LEGO elements in original factory condition (except LEGO string and tubing may be cut to length), and must conform to the following quantity limits on electrical parts, no matter what you intend to use or connect or attach to the robot at any one time:
For RCX users: For NXT users:
RCX controller (1) NXT controller (1)
motors (3) motors (3)
touch sensors (2) touch sensors (2)
light sensors (2) light sensors (2)
lamp (1) lamp (1)
rotation sensors (3) rotation sensors (3 minus the number of NXT motors present)
3rd touch OR light sensor (1) ultrasonic sensor (1)
LEGO wires and converter cables are allowed as needed. Spare/alternate electrical parts are allowed in the pit area. Objects functioning as remote controls are not allowed anywhere. There are no restrictions on the quantity or source of non-electric LEGO pieces. Wind-up/pull-back “motors” are allowed, and do not count as motors. Pneumatics are allowed. Marker may be used for owner identification in hidden areas only. Paint, tape, glue, oil, etc. are not allowed. Stickers are not allowed except LEGO stickers applied per LEGO instructions.