[michael_obrien]

You could use idle sprockets to guide the chain but you could also use a rounded piece of HDPE or other low friction material bolted to the frame to save weight and machining/shipping time. I don't know if this has been done in FIRST but I remember it on some battlebots... if you need a picture I could find one.

EDIT:
picture
close up
detatched

this isn't exactly what I was talking about but you see how the yellow plastic bit is being used.