For me, I'm not very consistent, so it tends to vary depending on whether or not I have an assignment due soon-ish. (My modules - not specifically Engineering ones, although a couple of them can be - tend not to be ones with exams). I might do little or nothing for a couple of weeks when nothing is due; but when there is something I need to hand in I've been known to do 40 hours or so a week (for a 60-credit module).