A quadrupedal robot inspired by the basilisk lizard was developed and modeled with a 3-D real time simulation. Due to the robot's geometry, leg motion, and water interactions, the net pitch moment at the center of mass is not zero making pitch motion unstable. This paper introduces two types of tails, passive and active, to stabilize pitch motion and analyzes the advantages and disadvantages of each. It is shown in simulation that a purely passive tail can stabilize pitch motion and lead to a

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... eady state robot pitch angle in the absence of disturbances. It is further shown that an active tail can compensate for disturbances and correct any drift in the robot body pitch angle due to changes in robot running speed.