Here's a machine that should (should) allow somebody with little training to strum up to eight chords on a guitar. This could be used by somebody with a handicap, or simply somebody who'd like to strum along to their favorite tunes without learning all that complicated finger pattern stuff.
Chords it plays (as designed) are major chords for D,C,A,G and E. Minor chords for e,a,d. That spells DeadCAGE for some reason... That combination of chords will allows you to strum hundreds of thousands of songs.
I have made three prototypes of this, and they work to some degree. I'm uploading it as a work in progress. Having spent months of effort to get this far, I hope that somebody picks it up with renewed enthusiasm and improves on my design. It is fairly complex, but I include full assembly instructions, where I got the non-printed parts, lesson learned and suggested improvements. Good luck. If anybody gets real enthusiastic I'd be happy to share video of the thing working, on a guitar.
Update: Here is a quick youtube video of it in action. Sorry to say the guitar was not in great tune, but you get the idea:
20% for most, 100% for the hammers
Up to you...