My first attempt at a 'budget' dosing peristaltic pump, mixing some design concepts together from some previous, related designs. You can find more info on the design, and I will be continuing to add related designs, here.

One of the main concepts I was trying to test here was the use of bearing balls instead of the traditional full rolling element bearing for the contact with the tube.

The other, was having this be a modular design that could be chained together with other components using the same stepper. The reasoning being to enable each section to have a different diameter of tubing, and therefore a different flow rate per step. This would make it easier to have the one pump handle the full range of desired tasks, from precision dosing of mL (or sub-mL) volumes to pumping at a rate sufficient to water a planter box at Liters per minutes.

Ultimately the design didn't provide sufficient sealing with the spherical contacts to give the desired control over the flow. But I wanted to share the design to see if others might have a use for it, or, even better, might build off of it and make it better! 

Design Overview

The rotor has conical recesses that the steel balls seat into, and the rotor is held inside the two housings. As the cross section below shows, the tubing is wrapped through half of this pathway and it is compressed between the balls and the housing walls. 

The housings each have a v-groove ring that serves as an alignment feature to additional modules by putting spheres between the mating v-grooves.

Also to support the modular goal, each side of the pump module has the same, female coupler.