Peristaltic pump with stepper motor

[iLMaRiO]

Ok, I admit, i'm unable to create a working rotor for a peristaltic pump.
I'm using a slightly customized version of the pump (0.8mm ID) from alkabot: https://github.com/robotfishe/alkabot/tree/main/3Dprint

The "stock" rotor has a distance between bearings and the stator hole, around 1.80mm
This value won't match with any thinkering: a proper rotor should keep bearings at a distance of twice the hose wall thickness, this because the silicon hose when squeezed will get the size of twice wall thikness (you are squezzing and so both walls with match)

a tube with 0.8ID/4 OD like the one suggested in alkabot, has a wall thickness of : "(4 - 0.8)/2" = 1.6mm
keeping a distance of 1.80 results in a non sealed squeeze (thus the water wont rise)

On my own, i've tried with more or less 40 different rotors, with bearings of different sizes and I still have to find the right measurement.
The math doesn't help, because keeping the twice wall thickenss doesn't seal, so i've tried with -0.1 , -0,2 and so on, but honestly I don't like this approach, too many try and error.

Which is the math behind a peristaltic pump ? Applying the exact math and using the excat value for wall thickns, doesn't work.

am I miss something ?

 

[iLMaRiO]

this is what i'm talking about:

red: stator, the hose is squeezed against this wall
green: sto bearings and stock rotor from git-hib
purple: my bearings and my rotor
light brown: stock rotor with bearings

as you can see, the green one, should squeeze properly, becase the bearings is touching the hose and it's squeezing against a hose thickness of 0.8mm (total 1.6mm wall thickness)

mine, the green, doesn't work, but i's made exactly with the math formula: WallTotalThickness=(OD-ID/2)mm

So, what's wrong here ?