[abstFig src='/00290003/02.jpg' width='300' text='Underactuated rimless wheel model for collisionless walking' ] In this paper, control methods for achieving collisionless walking of robotic underactuated walkers are discussed. Collisionless walking is a gait type of motion that does not cause collision during the landing of the swing-leg end. First, we introduce a simple point-footed walker and develop its motion equation. Second, we propose two time-scale output deadbeat control approaches and demonstrate mathematically their ability to generate a stable, collisionless walking gait. Overcoming potential barriers at midstance as well as the stability of zero dynamics are guaranteed accordingly. Furthermore, we investigate fundamental gait properties through numerical simulations.