Shielded cable is the proper way and should really be used and like Swarf says just buy CY cable if you do.
You'll find it here cheap enough and just use 4 core 0.5mm or 0.75mm. CY Cable
Only ground the ends at the control box and make sure your control box uses star grounding. IE all grounds to same spot.
Note he just means one end of the cable and not both. On the other hand you may get away with it and it all work fine? i did on my first one and that was a can a of worms. Saying that set it up right first time and you will have less problems to sort out later (spending hours guessing what the problem is).

Bloody nice job by the way and a credit to the build so far. You have worked very hard ;-)