Free Spirit

For about one year, the NASA exploration vehicle, Spirit, has been stuck in the sand. The rover relies on wheels. In soft soil, the wheels can sink above the axles and fail.

Robot developers would like to add some legs as an alternative mode of transport to go where wheels cannot. Robotics would like more information from model systems on walking mechanisms that provide stability and resistance to becoming stuck.

Analyzing the 3D movements of insects is not easy. They are small and even small reflectors, like the ones the movies use for 3D animation are too large for most insects. The preferred model insect for studies of walking is the cockroach. Cockroaches are easy to rear and comparatively large insects. A group led by John Bender at Case Western has recently developed a computer system for analyzing the movements of cockroaches. They add reflective paint to cockroach legs instead of attaching reflectors as in 3D Animation. Their system was verified using tethered cockroaches, but may be applied to free walking cockroach. Very large numbers of images must be analyzed to model the movement accurately. Computers can process the images more rapidly, decreasing the time it takes to analyze the images.

Cockroach movements are dictated in large part by the structure of the legs and the materials they contain. When walking, cockroaches use an alternating triangle motion. They move the front and back legs on one side and the middle leg on the opposite side. At the same time, the opposite side front and back legs and the middle leg on the same side are planted. The motion in the joints of the planted legs is responsible for much of the movement. The leg joints contain the springy polymer, resilin, that smooths the motion. The moving legs must “find” the surface and plant at a new position.

Insects have developed sophisticated methods of walking through millions of years of evolution. We can take advantage of the many years of trial and error to develop our own walking robots.

Will walking robots avoid getting stuck? That is an important question. A good field entomologist will tell you that insects can and do get stuck in the environment. Legs are not as efficient as wheels for long flat distances. It may be possible to address these limitations of walking by robots that incorporate both wheels for efficient distance travel and legs for terrain that is unsuitable for walking. Cockroaches are not foremost inspiring insects. However, they are providing bio-inspiration for the robot world.