Summary

This is an attempt to design a small, continuous-rotation servo powered two-wheel rover that can carry a Raspberry Pi. The idea was to modify two cheap 9g servos to provide continuous rotation output on the two main wheels, with an additional passive swiveling front wheel. The servos were modified by drilling out the output shaft enough so it no longer rotates the feedback potentiometer (set to the center position - to be on the safe side, I also added a drop of glue to the potentiometer).
I added grooves for rubber O-rings (found at the hardware store plumbing section) on the big wheels to add traction.
I have driven the rover around with a regular RC receiver, the Raspberry Pi has yet to be added.
There is an STL for the full assembly included - in order to print it, you should download the OpenSCAD source and export the individual sub-components separately (two big wheels, front wheel, base, front 'suspension'). I used two small ball bearings from a broken RC helicopter (5mm diameter, I believe) for the front wheel swiveling and rotating axis.