Even if the FAs do let you on board with it....taking up so much room in an overhead is going to leave you with some really ticked off nearby pax. Ask the FA to put it in his/her closet and they will most likely make you gate check it.

I have a 26" and while it doesn't weigh 50 lbs when full...I don't even want to think about having to lift that into an overhead...or anyone else having to either.