2+1 = 4 . This robot’s function is a special drive train called a Motor Multiplexer. It works by having 2 motors to drive the vehicle, and another motor in between the 2 to slide them forward along a gear rack. When they are in the front position a bump sensor is pressed, and it stops the center motor. The 2 motors are now disengaged from the wheels, and engaged to the 2 worm gear-boxes on the front, which have attachments on them. So, basically, it’s purpose is to have 2 powered drive wheels and 2 powered attachments, with only 3 motors. It was originally designed for FLL.

Video Found Here: LEGO MINDSTORMS Motor Multiplexor