Reactive free-gait generation to follow arbitrary trajectories with a hexapod robot

We present a reactive controller that is able to displace a legged robot along an arbitrary trajectory with a high degree of accuracy. We designed the different modules of our controller so that they can deal with arbitrary leg configurations. In this way, any leg movement necessary to overcome unexpected terrain irregularities can be correctly compensated by the controller, while still following the trajectory commanded by the user. Since we move the robot as a reaction to leg movements while stepping, the speed of the robot is automatically adjusted to the terrain profile: the more obstacles in the terrain, the more leg movements necessary to overcome them, and the slower the movement of the robot. We prove that, as the terrain becomes simpler, so does the gait generated by our controller, automatically converging to the tripod gait when the terrain becomes flat. This is achieved without requiring a map of the terrain and, thus, our controller can be used by robots with minimum computational and sensing capabilities. The results we report using different legged robots and in different environments prove the adequacy of our approach.