you can shift on the fly with out a clutch. this year we used an air cylinder to changed gears by engaging them with a 3 tooth dog. This is by far the easiest way to do on the fly shifting.
Cars use clutchs because it wouldn't make sense to turn off the engine every time you want to change gears (changing gears on the fly does not mean you want to keep throwing power into the system as you shift to hard on the shifting mechanism)
Some good pics on our 2003 drive
http://www.chiefdelphi.com/forums/pi...gle&picid=3611
http://www.chiefdelphi.com/forums/pi...gle&picid=3601
http://www.chiefdelphi.com/forums/pi...gle&picid=3707
also look in the white papers for team 45's 6 motor drive from 2002 that what we based ours from.
Anything else you want to know about our drive let me know