While my team has never built what I would consider a true WC drive train, we have incorporated at least one element of WCD in all but our rookie year. First of all, my understanding of the definition of WC vs traditional skid steer:
Common elements:
- Both traditional and WC normally have 6 simple (non-roller) wheels with a drop center, though variants of each with additional wheels and/or omni on the corners exist.
- There is no notable difference in software required; you have two banks of motors, one on either side. Either may have one, two, three, (or occasionally more) motors per side.
- Either can be used with a single speed or shifting gearbox.
- [Edit]Any articulated drive train does not properly fit either category, though an articulated gearbox may be extended from either design.
Distinctions:
- West coast drives feature cantilevered drive shafts; traditional has a bearing on either side of the wheel.
- West coast drives provide direct drive to at least one wheel on either side, usually (if not always) the one closest to the center of gravity of the robot; traditional usually had chain or belt to all wheels, though direct drive is now common in non-WC drive trains, including the 2014-2016 KoP chassis.
- WCD usually employs tube (though occasionally channel with the opening on top or bottom) in order to support the cantilever; traditional usually employs channel with the opening inboard or outboard, or vertical plate, most commonly bent inboard or outboard at the top and/or bottom.
Note that there are also drives which incorporate these features mix-and-match. The common example which comes to mind first is the (recently discontinued?) Andy Mark nano tube chassis. It has direct drive on four cantilevered axles, but these are the two corners, NOT the one usually nearest the CoG. Our second and third year drive trains also featured direct-drive wheels on cantilevered axes, but for similar reasons were clearly not WC drive trains [Edit: Our 2013 robot only had two driven wheels and two idle omnis, whereas our 2014 robot had mecanum drive; we learned a lot from these mistakes].
Advantages of WC:
- Easier to change wheels by removing a single lug screw, snap ring, shaft collar, or clip.
- Reliability despite failure of chain, as the axle nearest the CoG is direct driven (though this feature is now on some newer "traditional" drive trains)
- Track width can be a greater proportion of robot width, as there is no need for an outer plate/channel (other than to meet bumper support rules)
Advantages of traditional skid steer:
- You are much less likely to bend an axle. (I never saw an FRC axle with a bearing on both sides of the wheel bent until STRONGHOLD.)
- Requires less precision in machining (though this can now be mitigated with dollars by buying a COTS WC chassis kit).
- [in recent years] Available through the KoP chassis program at little or no dollar cost, as a kit which can be assembled in a remarkably small number of worker hours.