I have a background in programming, but a program by itself has limited use. I was like, man, I need to make a project that will actually control something. I had my old mini-fridge from college lying around and, I thought, how about an iPhone-controlled drink vending machine? So I did it . . . and it sucked. You could control it from your living room—or from China—but the cans just rolled out onto the floor. It was a pain to walk over and get them. I wanted to get a beer to travel from the fridge across a room with minimal effort and maximum cool.
I called my friend Graham Phero, and we started building a new version. We thought it would be awesome to use compressed air to propel the cans, but we had no idea how much pressure to use. We started with 100 psi and destroyed a can of beer on the ceiling of a garage. After that, we started at 10 psi and worked up.
Slowly the rest of the project began to take shape. The vending mechanism is a series of slanted shelves built inside the fridge, with a servo at each end. The beer is funneled into a cannon, and the whole thing is mounted on a lazy susan, allowing it to turn so you can aim the throw. My friend Josh Lilly helped me design an iPhone app that could select a beverage, aim the cannon, and fire it.
Time: 2 Days
Drink Storage: The shelves angle down slightly so the cans roll to the dispenser. At the lower end, an arm attached to a servomotor holds the cans in place. When the servo receives a signal to retract, a can is sent through a cutout in the fridge and into the cannon barrel.
Air Supply: An air compressor plugs into the wall and connects by a hose to the expansion tank, a short, capped PVC pipe. A regulator valve between them controls the pressure in the tank. Optimal pressure for lobbing a can of beer 15 feet: 45 psi.
Valve: A sprinkler valve plugs into the expansion tank and holds the pressurized air in until you’re ready to fire. It’s attached to an electric relay that will open it for a tenth of a second, releasing the air from the tank and forcing it down the barrel.
Barrel: The barrel pipe should be just wide enough to accommodate a can without creating excessive friction. Too much space between the can and the barrel wall will let air escape past the can and diminish pressure.
Turret: The whole assembly sits on top of a Lazy Susan. Using a fixed joint that provides a 90-degree turning radius, a servo moves the assembly to aim the throw.
Microcontroller: An ioBridge 204 microcontroller, which lets users control devices via the Internet, is the brains of the operation. It connects to the vending and turning servos and has an Ethernet port to link to the Web.
Relay Board: When the app commands the robot to toss you a beer, the message is directed to the relay board, which directs a pulse of current from a nine-volt battery to the sprinkler valve, opening it momentarily so the cannon can fire.
The App: The vend button sets off a series of commands. First the servo for the selected drink’s shelf drops, pausing to let a can roll by. The door on the front of the fridge housing opens, and you aim with the left and right arrows.
Rusnak is getting a master’s degree in Human-Computer Interaction at Carnegie Mellon University in the fall. You can get full instructions to build the project and search for “Beer Cannon Controller” in the iTunes store to download the app for free.