Zach Hoeken wrote up a nice piece about the design of the MakerBot Frostruder MK2, currently in its second prototype. He talks about the challenges of designing a cheap, small device capable of computer-controlled cupcake frosting:
My first experiment was with some thick, chocolate frosting that you can find in nearly any grocery store. I simply wanted to see if it was possible to use air pressure to extrude frosting, so I wired up a solenoid to a switch and used that solenoid to turn the air pressure on and off to the syringe. I was using a 21GA (0.53mm) needle and a standard 60cc syringe. I hooked it up to the air pressure and opened the valve. Nothing happened right away, but I gradually turned the pressure up until about 50-60 PSI I started getting a frosting extrusion. I kept turning up the pressure to about 80 PSI where I got a really nice, very fast frosting extrusion that was about 0.5mm wide. Success!!!
From MAKE magazine:
In MAKE, Volume 19: Robots, Rovers, and Drones, learn how to make a model plane with an autopilot and a built-in robot brain. We’ll also show you how to make a comfortable chair and footstool out of a single sheet of plywood, a bicyclist’s vest that shows how fast you’re going, and projects that introduce you to servomotors. All this, and lots more, in MAKE, Volume 19! Subscribe here, or buy the issue in the Maker Shed.