I am working on the drive system for an OEM that builds railroad maintenance equipment. Usually their machines are built for use on railroad tracks. This machine, however, will use two CAT track systems for ground mobility. The GVW empty is 120,000 lb, and full load could be upwards of 250,000 lb, depending on the average density of the iron ore it will be loading and transporting. This means possibly 125,000 lb supported by each set of tracks, assuming even distribution of the weight (not the case, but assume true for sake of simplicity at this point). The largest problem, I think, is the dimensions of this machine. It is roughly the shape of a railcar - long and narrow. To be specific, the dimensions from center to center of the tracks and width are 30 ft x 10 ft. Not the ideal ratio of dims to apply a skid steer.
Two design directions at the moment: steer both sets of tracks with differential flow, or steer one set (front) and fix the other (rear). What I would like to know is how to roughly spec a system like this (pumps, hyd motors, torque specs). I assume something needs to be known about friction coefficients and associated forces on the tracks. Ultimately, can this machine be steered in this way?