that's pretty cool. I tried making an unofficial one during the build season. I connected two alligator clip wires to a 14.4 V battery to a 4" muffin fan. I had some problems, because the alligator clips (which were metal and unshielded), touched and a wire burned, pretty badly. I don't think i'll work with circuits again.
Anyways, about the K'nex thing, its great if you can get it to work with other devices. I have played with K'nex for about 11 years now and I have had a lot of trouble making it work with other devices, such as coffee cans, etc. Since the K'nex rods and connectors are not of a uniform length (that is a rational number, in inches or centimeters), it is very hard making it work with objects that have rational numbers of lengths. Congratulations!!
P.S. don't use alligator clips!!!