Abstract
This paper addressed the motion of passive dynamic walking mechanism on a flat floor. We made a simple linkage machine which omits ankle joints, knee joints and an upper body. In our previous works, we have proposed the consistency of natural frequencies in swing and rocking motion is important for energy-effective passive walking. In this paper, we discussed on the unexpected waist motion. Then, we showed the sub-system which moves like an upper body is effective for avoiding the unexpected waist motion. Sub-system on the waist makes the motion of swing and waist in-phase. Therefore, the steps of test machine may be increased.
