the peristaltic pump
We built a persitaltic pump to be capable of extracting the liquid from the tank without contaminating it.
In this case we use a stepper motor from an old printer. This motor executes 1770 steps to transport 10ml from one container to the other one, after that it does 1000 steps in the opposite direction to return the surplus of the sucked liquid that remains in the tube to the original container.
We improved the pump putting 8 skate bearings, 2 for each axis, to have more suction power, reducing the speed of the spin but increasing the power, looking for the optimum balance between these two variables.
The extraction is not always as precise as in the video, 2 ml up or down, but counting on this margin it works well for us.