I wouldn't think of "raising and lowering the drive train" but instead I would think of "raising and lowering the tote."
Here is a masterfully done CAD rendering of an idea:
http://imgur.com/4ebNHBF
Use a winch in the middle, some cable, and some pulleys, to hoist the tote up around the drive base, and then set it down. All motor-driven, no drive articulation, and you could easily take all of the robot guts out of the tote to work on them.