Hello Jack, the common scale is 14th, as that's what the trk kits are & most of the constr machinery is tailored to work with them. Check out RcLogger and tracksandtreadslou in the Constr Equip forum, both have logging backgrounds from the BC area & have built various rc model logging machines... my best advice for you is start reading, there are threads full of information that spell everything out clearly.
Welcome to forum.
