It’s officially the holiday season, and for some of us, that means partaking in the ubiquitous and inevitable jello shot ritual. Now, most of us just down shots without giving the ingredients or appearance all that much thought. However, a Maker by the name of Sprite_tm recently realized something was missing from the contents of his cup, namely a design. In other words, what if a bartender could print actual designs inside a jello shot?
As a result, Sprite_tm quickly grabbed a syringe and injected food dye into one of the jello shots, successfully creating a pattern of sorts. Ultimately realizing it would simply take too long to execute each jello shot by hand, Sprite_tm decided to whip up a specialized 3D printer for the alcohol infused task.
After some looking around, the Maker found an old stack of CD_ROM and DVD drives, which he used to create a three-axis moving platform. Sprite_tm utilized a forth drive’s ejector assembly to depress a syringe which extruded a concoction of banana liquor, green food dye and corn starch through small tubing to the ink-head.
To power the device, the Maker chose an ATTiny2313 along with some stepper motors drivers and a transistor to drive the tray motor.
On the software side, the stepper motors are controlled using micro-stepping. As Sprite_Tm explains, steppers like this have (at max) 8 angles by simply sending DC through the coils.
“The firmware improves on this meager resolution by doing a sort-of PWM between two of the main angles: you can make the motor turn to eg. 15 degrees by telling it to go to 0 degrees for two milliseconds, then then telling it to go to 45 milliseconds and repeating that. Apart from that, there’s also a PWM going on to switch the motors off and on,” he notes. “The rest of the program basically consists of a bunch of coordinates for the figures, and some logic to move the needle point around. Again, all this is written for efficiency but has some drawbacks resulting from that. For example, the routine to move in a straight line uses 16bit fixed-point values with only 3 bits behind the decimal point, meaning quite some imprecision in the angles the lines can draw.”
With time of the essence, the Maker was only able to hardcode two figures into the firmware: a box and a spiral. Although simple, these figures offer some pretty nice effects ideal for any holiday party! Don’t forget to check out the project’s official page here.