With limited building skills and a newly acquired second RCX, I built a somewhat ugly robotic base for the 8421 crane set, back in November 2006. The grabber is from the the Mindstorms Ultimate Builders Set. It features a Lego Speed computer as a rotation sensor. The crane module is more or less unaltered, except for added motors to control the switches. A racing buggy motor is used to power a compressor, as well as a switch to open and close the grabber. Check out the pictures below for more.
