Kousoku Denjin Albegus

Three talented students of a technical high school, Daisaku, Tetsuya and Hotaru create award-winning robots as part of a school competition. At this time, the evil Derinja race that plans control of all space extends its ambitions to Earth. To combat this threat, Hotaru's father, Professor Mizuki, takes the three robots and modifies them for battle. Albegas, a super robot, is born.
(Source: Wikipedia)