Several months ago, my friends and I built a bar-bot, a machine for serving alcoholic drinks.  The original motivation was a Robot Birthday party at my house; traditionally we have a theme drink for each party, but it turns out there really are not any "robot drinks" (bender not withstanding).  So the obvious step was a make a robot make the drinks :-).  I've wanted to make such a machine anyway since attending a barbot party in San Francisco about 5 years ago, at which about a dozen such machines were exhibited.  After looking into how expensive various components would be, I settled on using 12V peristaltic pumps used for aquarium dosing, because they are both cheap and food safe.  The biggest downside was slow - they pump about 80ml/min (don't believe 100ml/min claim), so realistically it's about 25 seconds/ounce.  That suffices for the booze, but for mixers I needed a higher flow rate, so I found a cheap way to make a valve (basically just using a servo motor to crimp close some tubing), and just gravity to drive the flow.  A friend of mine did all the design for the laser cut boxes, another did the coding, and a third helped me with assembly.  I did all the electronics design and the project management, plus all the actual buying of things (we love you plastic world and creatron).  It was super huge amounts of fun, and I've used it at three parties now, each time it was a smash hit.  The lighting (we used fully controllable RGB LED strip - the expensive stuff) is spectacular, that's why we called it the Luma Droid!   All told, the machine cost $470 in parts, took 71 hours of my time, and about 60 hours of my friends time.  So I estimate time payback (assuming 30 seconds of saved time per drink made) in about a millennium :-).    Financial payback, however, may take slightly less long - I've just been offered quite a bit of money to improve the machine (in whatever ways I want) and bring it to a very swanky party for a top-tier alcohol brand.  So that's exciting!  Check out the Luma Droid photo gallery.   Here's a video of Luma Droid in operation at the birthday party: