Oilfield Trash and or artstegall, thanks for your

Oilfield Trash and or artstegall, thanks for your continued subject matter expertise knowledge and contribution to the board.  Since I'm a mechanical engineer;  I am interested in how they turn a drill 90 deg to go lateral?  I saw an illustration once that showed the possibility of flexible piping forming along a large radius i.e. possibly an eliptical type turn?  What devices do they use when lateral drilling? Some form of u-joints?  Flexible bellows? Just curious! Thanks again!