In this paper, we described a technique for the swing-up control of a 2 link acrobat robot using a cannonical form which is derived form the law of conservation of an angular momentum based on the center of the first joint. The wide usefulness of the canonical form of the acrobat robot, which was suggested here, is could also be applied to control a free flying robot or an underactuated planar manipulator with no gravity term. Some simulation results are provided to verify the effectiveness of the proposed algorithm