How about this - get a long screw with a flat sided nut on it that will sit inside a square column such that the screw is held in place and turning it back & forth causes the nut to move up & down the screw.
One wall has slot down its length, and eyelet attached to the nut (or sandwiched between 2 nuts) then moves up & down as screw is turned.
Attach a motor to the screwhead - or mount a cordless screw driver over the head of the screw and have the arduino control the screwdriver.
http://www.blackanddecker.com/power-tools/9074CTN%20A.aspx $15 if look around