I've been trying to recreate the Useless Machine found here: http://www.youtube.com/watch?v=QdKtgfmfA7s&feature=c4-overview&playnext=1&list=TLp4R5S7LPESk
In the description, there's a link to a brickshelf gallery that has detailed pictures of the insides of the machine: http://www.brickshelf.com/cgi-bin/gallery.cgi?f=416984
I think I've figured out most of the mechanism, but can't for the life of me figure out what motor is being used, and how the motor stops running once the arm is sufficiently retracted. There doesn't seem to be another switch hiding at the bottom... Those two things have just been bugging me for a while.
First post here, I'm only just getting into LEGO, thanks for the help!