<p>To realize rough-terrain vehicles with omi-directional motion, the authors have developed the “Mecanum crank,” which consists of Mecanum wheels and “crank wheels.”. To improve the rough-terrain locomotion of the Mecanum crank, this paper describes a design method for the crank legs that enhances the climbable step height. To improve the climbable step height, we focus on four dominant physical phenomena(jamming, hooking of the crank legs, slippage of wheels, and tumbling). Because the climbable step height increases as the vehicle and wheel size increases, this paper discusses the relationship between the maximum climbable step height and the size limitation. Thus, the proposed method maximizes the climbable step height relative to the wheel diameter within the size limitation. The experimental results for step climbing reveal that the proposed method increases the climbable step height from 95% to 160% of the Mecanum wheel diameter. Moreover, we verify that the proposed method does not decrease the feasibility of stair climbing and horizontal-gap traversing.</p>