Per Tim's earlier quote regarding the driven wheels:
"It will work in areas where there is not much lubrication or heavy loads, but will frequently fail throughout a typical days ride.... Fail meaning simply start uncontrollably slipping the remaining driven wheel or wheels inside of the track so that the machine essentially goes nowhere."
I once sheared an axle pin on a machine which took me down to one wheel driving an Adair tracked machine. I was far back in a swamp with two other machines without tracks. Yes, I noticed the one side wasn't pulling as well as the other, but I managed to keep going until I found a side trail out and in fact towed the other machines out of several obstacles. It would be a much simpler machine to have one driven wheel per side. I just wonder if a machine with one powered tire per side operating with a track system with maybe an automatic track tensioner might be the ticket.
Simple in design, cost effective, etc. Maybe not quite as capable as a machine with all driven wheels, but probably good enough.