Here are the drivetrain trends. I see a trend for skid steers. I left blank information that I either didn't know or couldn't find.
2010
67 – 8 WD long
177 – 8 WD long (articulated is sets of two, front and back)
294 - 6WD long
2009
67 - 6WD wide
111 - 4 wheel crab (non-coaxial), wide
971 - 6WD wide
2008
1114 - 6WD long
217 - 6WD long
148 - three-wheeled crab (coaxial), nonagon-shaped robot
2007
177 - 6WD long
987 - 6WD long
190 - 6WD long
2006
217 - 6WD long
522 - Treads, long
296 - 2WD long, Omnis in front
2005
67 - three-wheeled crab (non-coaxial). Flop bot.
330 - 6WD long
503 – 4WD long, omniwheels in rear
2004
71 - 4WD long
494 - 4WD long
435 - 2WD long, with casters in front
2003
111 - Four-wheeled non-coaxial crab (with dropdown skid for turning)
469 – 4WD Long
65 - 4WD Wide
2002
71 - 4WD flop bot with casters in front
173 - 4WD long
66 – 4WD long
2001
71 - ?
294 - ?
125 - ?
365 - ?
279 - ?
2000
255 - ?
232 - ?
25 - ?
1999
176 - 4WD long w/ Omnis in front
1 - tank treads, long
48 – 4WD, long
1998
45 – 4WD long with Omnis in front.
1997
71 - ?
1996
73 - ?
1995
100 - ?
1994
144 - ?
1993
148 - ?
1992
126 - ?
(I just compiled the information from this thread
http://www.chiefdelphi.com/forums/sh...ad.php?t=77412)