pic: 3-speed lego geerbox
 

Very nice and compact, but it will also have the same problems that I had said about rlowerr's design

Again, this isn't an attack :)

nice, but dont you have any problems with the spacing? By the looks of it you could be in two gears at the same time... which would not be good.

Also where are the motors? Get that thing running!

I just took it apart to build an incomplete planitary g-box

He should be fine with spacing, put 3 fingers on the screen, one over each of the shifting gears. Slide your hand a bit and see where each one lines up when the other meshes. You'll see each one should cleanly be going into the next (less the forced mesh). Now yes, I don't think Tytus busted out a micrometer to make sure that it all works correctly, but it's within a millimeter of working. (Can't prove yes or no because I can't touch it)