the support polygon
is the rectangle ABCD with the size of 160 mm × 130 mm
which is the contacting rectangle of the four wheels on the
ground. The robot goes into three extreme conditions when
the manipulator stretches out and points to the forward, left,
and right directions of the robot. The left and right directions
are symmetrical. The conditions when the manipulator points
to the forward and left directions are analyzed. In these
conditions, the ZMP is near the borderline of the support
polygon. As shown in Fig. 6 (a) and (c), the ZMP is within the
support rectangle. The robot is stable in the two extreme