In this paper, several models of approximating ZMP for humanoid are proposed without force sensors. Generally, ZMP is determined by using force sensor information. In this paper, this torque information is estimated by measuring motor-driving current. This paper discusses several estimation models whose results are compared by experiments. Furthermore, we examined effectiveness of proposed
... [Show full abstract] models. The results show that the proposed estimation methods are effective in semi-static condition. Specially, these proposed methods have advantages when a humanoid without a force sensor is controlled under change of gravity direction such as a slope condition.