4 Lateral Rolling

PYP also can perform a lateral rolling gait (Figureb). The restrictions are the same as in lateral shift but the amplitude of the waves are greater or equal than 60: $A_{1}=A_{2}=A_{3}>=60$.

When PYP rolls $90^{o}$ it is converted into a YPY (yaw-pitch-yaw) configuration. Now, it only has one module on the pitch axis. Therefore, it cannot move forward or backward. But lateral shift or lateral rolling can still be achieved. When lateral rolling is performed, configurations PYP and YPY appears alternatively.