In the back of my mind there is an image of a wind up device that writes in a sort of flowing script with an ergonomic key layout, the center like an armilary sphere with the page coming out of the left right axis on top.
That would be a fun project. Check out Jaquet-Droz's "Writer"
http://en.wikipedia.org/wiki/Jaquet-Droz_automata, a doll which really does write text with pen and ink by entirely mechanical means. That was built in 1774. I've seen it; once a month the museum in Neuchâtel, Switzerland demonstrates it.
The arm movements of the Writer are driven by a stack of cams. The stack is positioned along its axis, like a jukebox, to select the next character to be written. The characters to be written are controlled by a set of stops on a wheel, with different length stops for each character. The length of the stop determines the position of the cam stack, thus selecting the character. Here's a video:
http://www.flickr.com/photos/danrn/3256939768/#secrete3b72032bd-w500-h375.
There' also the Musician and the Draughtsman. They're beautiful pieces of machinery. All three dolls are still working; Swiss watchmakers maintain them.
The Writer shows a possible mechanism for a typewriter as suggested. The cam stack is still a reasonable idea, but cam stack positioning needs to be improved. Positioning by length alone is too unreliable; the Writer in fact sometimes prints the wrong character. Many mechanical typewriters have been built that positioned a typing element based on which key was pressed; the Hammond and the Blickensderfer worked that way and were useful machines produced in volume. So there are some mechanisms
you can copy for positioning the cam stack.
If you're willing to make the machine using modern technology, it's not so bad. The cam stack is a complex part, but it would be straightforward to machine the entire stack as one piece on a CNC mill.
I'd suggest getting a good understanding of how the Jacquet-Droz writer works, how a Blickensderfer typewriter works, and learn to use SolidWorks.
