The voltage sensing voltage divider is on the high side on the R2, thus can only sense supply voltage. This should be moved to the low side of the electromagnet, so it can be utilized to sense the true magnet voltage, as opposed to the curve-fitted static experiment. This feature would simplify data gathering for the curve fitting experiment, and could possibly aid the creation of a self-calibration feature.
The ring holding the magnet cage covers the logo partially. The logo can fit below the potentiometer.
There should be a circle or some other markings aiding the positioning of the ring holding the cage, so that its assembled more easily. (There was one on the R1, I have deleted it by mistake).
Move the magnet high/low side (+/-) stencil to the other side closer to the cage, because the superstructure covers it and it cannot be seen.
The magnet needs only about 60 mA current. The reason for the external source is the voltage, not current. How about a voltage booster from 5 V to 12 V (or even 24 V, however, that is not really needed...)
The non-saturated range of the MOSFET is way too low, essentially limiting the resolution of the output. We should use another type of power element that is less saturated so that we can achieve finer control of the power sent to the magnet.
Achieving more range (height) should be strongly considered.
For the next release of the MagnetoShield: