I've built this syringe pump following those instructions. Now I would need how do I calculate the output pressure given the step rate of the stepper motor, and vice-versa.
I don't know if it is helpful anyway but I know that the relationship between the torque exerted by the motor and the linear force upon the syringe plunger is given by:
$$M = F r_a \tan(\alpha), \; \tan(\alpha) = \frac{p}{2 \pi r_a}$$
where $r_a$ is the radius of the threaded rod, $\alpha$ the thread angle and $p$ the pitch.
Thus we have:
$$M = \frac{F p}{2 \pi} = \frac{P r^2 p}{2}$$
where $r$ is the syringe radius. Is it right until now? Moreover, is it any useful? I found myself unwillingly stuck in this project but I never studied such cases.
The problem here is that the exerted torque depends on the load so I wouldn't know how to link output liquid pressure with motor step rate.