Most of the crab drives I have seen used the CIM motors on 2 wheels and the Drill motors on the other 2 wheels- although you would have to gear the motors up or down to a equal ratio. I'd reccomend you check out a robot with crab drive, email a team that has built one, and check out the whitepapers on gearing, etc- [Edit- You can only use the motors that are provided in that year's kit. If FIRST put 4 drill motors in next year's kit (highly unlikely) then you could use a 4 drill motor crab drive. Most likely, you'll have to figure out gear ratios and mess with the CIM and drill)
a crab drive is no simple mechanism, my team (5 years experience) has never built one... last year we witnessed a totally awesome, experienced team struggle through 3 competitions with no functional drive because they mistakenly made their crab drive external- so make SURE your drive is internal (i.e. wildstang, etc) so the crab modules are protected from impact. One hit, and you're dead- good luck with this undertaking, there's nothing better than the feeling when you finish
[edit] check out this whitepaper, ironically 226 used the bosch and FP
http://www.chiefdelphi.com/forums/pa...gle&paperid=73 [/edit]