Basically, the control problem of legged robot could be summarized in one point: all the legs are working together in such a way that the vehicle remains stable and moves according to the specified path. Legs are either in support phase, where they need to be coordinated to provide the desired body profile; or in swing phase, whose aim is to reach a convenient position to begin a new step. In a general way, the ground detection at the end of the swing phase is a keypoint in the walking algorithms. This paper focused on a DC actuator current measurement to detect interaction of a robot leg with the soil. It shows that careful sensing coupled with a comprehensive model of the system can give a quite accurate estimation of the contact force at the leg foot.