**Video materials**

*Biomimetics*

**Figure 13.**

**Figure 12** shows the transition of each leg's phase *ϕ*i. **Figure 12** also shows the phase difference between each leg and the left foreleg at low speed. The borders in **Figure 12** mean one cycle of gait. As **Figure 12** shows from the third step after the robot system start walking, each leg's phase differences were generated around 90° (0.5π rad). Also, the order of moving the legs is left fore (LF), right hind (RH), right fore (RF), and left hind (LH), which means that this gait is the same as the horse's walk gait. In this experiment, the legs' angular velocity while the legs were not on the floor was approximately 30°/s (0.52 rad/s). **Figure 13** shows the result at high speed. As **Figure 13** shows from the fourth step after the robot system start walking, each leg's phase difference was generated around 180° (π rad). Besides, the order of moving the legs is LF and RH, RF and LH, which means that this gait is the same as the horse's trot gait. In this experiment, the legs' angular velocity while the legs were

*Phase transition of the legs at high speed. (a) Trotting quadruped robot system and (b) each leg's phase transition and phase difference from the LF. The robot system generated the trot gait from an upright position.*

These results show that the quadruped robot system can generate gaits by reducing the legs' angular velocity depending on the pressure on the feet. Also, the robot system can generate different gaits depending on moving speed. Furthermore, the characteristics of the generated gaits are similar to the horse's gaits. In our control method, we confined the change factor in each leg's speed to feedback using weight-bearing balance. Therefore, we assume that the trigger for the break in the initial phase symmetry was slightly different in the robot's weight that the limbs were supporting. We have experimentally determined the parameters such as *θ* and *σ* that can stably produce these gestures. We expect that the dynamics simulator is necessary to determine these parameters quantitatively. In the future, we will use it

In this chapter, the authors constructed a quadruped robot controlled by the active gait generating method individually for four legs. The method is simply

not on the floor was approximately 51°/s (0.89 rad/s).

to analyze in detail how the parameters affect the gaits.

**30**

**5. Conclusions**

Additional video materials available at: https://bit.ly/3i91LbI
