*2.2. Static Side of the Problem—Construction Solution*

The primary goal of the robot construction was to maintain an anthropomorphic shape and to copy the original as best as possible in terms of physical properties. For the proper functioning of the robot, it was necessary that:


In order to fill the requirement that the construction design describes the shape of the human body as reliably as possible, one of the proportional models of the human body was chosen (Table 1). The selected model divides the distances between individual points on the human body into units of length. By observing the given proportions, it was possible to design a construction on a different scale while preserving the properties of the original. Since the shape of the body itself is not important in the LIPM model, but only the position of the center of gravity, the construction of the entire body of the robot was not absolutely necessary [13].

**Table 1.** Proportions of the human body according to the R.B. Hale model [13].


Subsequently, based on published information [6,14,15], an analysis of individual joints in the lower part of the human body was carried out (Table 2). A rotational degree of freedom was granted to a joint if its angle range exceeded 10◦ [16].



The design of the robot also depends on the level of system control. According to this criterion, walking robots are divided into controlled and passive walking robots. Controlled walking robots are those in which the range of each robot movement is given by a controlled quantity. Passive walking robots are kinematic chains that move stably with a step without control and without an energy source. The passive step concept can be applied to both quadrupedal and bipedal robots. The movement is achieved by an initial impulse relative to the system and an inclined pad along which the robot moves downwards. A key feature of passive walking robots is the curved foot. As a rule, the bending radius is equal to the distance of the center of gravity from the ground when the robot is in a rest state. Some controlled robots are also based on this concept, where the bending of the foot—completely or in the position of the heel and toe—improves the energy efficiency of the step and eliminates a step change in stability. A combination of controlled and passive joints in walking robots is also frequent. A typical example is the reduction of the knee joint in the robot's leg in exchange for a shock absorber. Another example is a robot leg composed of controlled joints in the hip and knee, or the other knee on the same leg, and a passive foot containing a spring in the toe. The stiffness of this spring ensures a flat foot shape in the secondary phases of the gait cycle, BAC 1 to 4 and later in BAC 7 to 8. In BAC phases 5 and 6, the foot bends under its own weight to such an extent that it directs part of the robot's weight into the toe, similar to human walking. Of course, both mentioned methods can be replaced by a controlled process. Usually, a combination of controlled and passive elements of the robot is used to simplify complicated movements that are more difficult to control [17,18].
