Having resolved the issue of dispensing the liquid components in a consistent manner, we were soon met with our next hurdle: How do we approach dispensing the ‘bubbles’ of our bubble tea? ‘Bubbles’, also known as boba or pearls, are the chewy tapioca balls integral to the bubble tea experience. These delightful pearls are often marinated in a thick, viscous sugar syrup that gives them their flavour and prevents them from drying out. Therein lay our troubles: while we had by now gained quite some experience in dispensing liquids, dispensing a combination of liquids (and a viscous one at that) and solids proved to be a completely different ball game.
(Credits: Bubble Panda)
Originally, we approached the problem by researching what we were less familiar with: solid dispensing. As mentioned in our earlier posts, one of the more promising options we looked into was the cereal dispenser. These dispensers often feature an airtight container with a rotating mechanism resembling a revolving door. With each turn of the knob, a fixed quantity of solids (corresponding to the volume of each quadrant) is dispensed. Encouraged by its ability to efficiently dispense a controlled amount of solids, we purchased a cereal dispenser with the intention of using a motor to automate it. However, the dispenser arrived with a crack in the container, making it impossible to test. Nonetheless, we examined the rotating mechanism and realised that it was not sufficiently watertight to prevent the leakage of the syrup solution.
(Credits: Food Network, 2022)
Unfazed, we went back to the drawing board and brainstormed more ideas for the gooey boba mixture. Eventually, we found a glimmer of hope in an ancient tool, the Archimedes’ screw pump. We found that the pump, composed of a rotating screw that displaces liquids and particles against gravity, had a variety of use cases including pumping sludge to clear land for agriculture, or delivering feed to farm animals. Some of these uses involved solid suspensions in liquids, hence we decided to test if the pump would work for our boba mixture. Surprisingly, despite the viscosity of the boba, initial tests with our 3D printed Archimedes’ screw pump prototype yielded promising results. The pump, powered by a stepper motor from the lab, had no difficulty pumping the boba mixture against gravity, even when the screw was positioned perpendicular to the ground.
(Credits: KSB)
Still, several issues remain. For one, we face an issue where the boba would get stuck at the top of the pump, rather then dispensing smoothly out through the spout of the dispenser. After resolving this, we would need to fine-tune the speed at which the motor should rotate, and the angle at which the pump should be placed to dispense our desired amount of boba.