Terrestrial mobile robots face diverse topographies while in field missions. Rough terrains cause the platform to oscillate, which is undesirable for some tasks. Robotic platforms with active tracked flippers can use such mechanisms to reach and maintain a leveled configuration while halted or moving. Thus, this work presents a posture controller that regulates the robot's orientation and contact plane clearance using flippers while the robot moves over unknown, uneven ground. The method takes as input the flippers' joint position, torque, and the robot chassis orientation, outputting as the command signal the flippers' joint velocities. Based on Stewart platforms, a differential kinematics model relates desired platform's motion to flippers' frame velocities. Later, a flippers-ground interaction model transforms their frames' computed velocities to flippers' joint speed commands. The controller is based on dual-quaternion algebra for generating the error signal. The efficacy of the proposed controller is evaluated experimentally in an industrial robotic platform moving as it moves along an open field track. The method successfully regulates the robot's posture while navigating over non-modeled rough terrain.