Of course we didn't want to continue measuring by hand so we built our own construction which is mostly composed of customized elements we designed using 123d design and printed with a 3d printer on our own.
We only used plastic because we didn’t want to have measuring deviations through metal and we used two stepper motors which should move the sensor through a kind of linkage, which is a parallel kinematic, meaning the motors can move the sensor without also being transported. Sadly this didn’t work well. We tried different threats but they slipped away, were so tight that the motors couldn’t move anymore or the single tracks moved shifted. We tried several designs, but could not get hold of proper belt drives like the ones being used in 3dprinters in time – we wanted to present our work at the youth science contest and had to develop another approach shorthanded…
And, yes, motors are made from metal and have a changing magnetic field around them during operation ;-)
We made sure that the motors (steppers) are far away enough not to influence the measurement itself – that’s why we tried to keep the motors outside the measurement area.