New Robot Mimics Cockroach Behavior to Traverse Through Obstacles

Engineers at Johns Hopkins University have studied movements of cockroaches by chasing them through an obstacle course, finding that the change in their movement was related to overcoming the prospective energy barriers and that they can jitter about to overcome obstacles in complex terrain. This team is the same that developed the snake robot and the cockroach robot.

The study results were reported in the Proceedings of the National Academy of Sciences on June 15^th, 2020.

Our findings will help make robots more robust and widen their range of movement in the real world.

Chen Li, Study Senior Author, Physicist, and Assistant Professor, Mechanical Engineering, Johns Hopkins University

According to Li, since mobile robots are on the brink of entering into society, it is crucial for them to move through their surroundings with efficiency and comfort.

A few mobile robots such as robot vacuums and self-driving cars already traverse flat surfaces and transition between moves well (for example, U-turns, forward drive, and stopping to avoid obstacles) around barriers.

However, several crucial uses like inspection and monitoring in buildings, space exploration through rocks, and search and rescue in rubble need robots to physically interact with their terrain to traverse, instead of simply avoiding, obstructions.

Search and rescue robots can’t operate solely by avoiding obstacles, like a vacuum robot would try to avoid a couch. These robots have to go through rubble, and to do so, they have to use different types of movement in three dimensions.

Ratan Othayoth, Study First Author and Graduate Student, Johns Hopkins University

Robots still find it difficult to do so since researchers do not have clear insights into how the physical interaction of a robot with complex terrain impacts its ability to shift between various movements. Such insights can enable scientists to construct more dynamic robots.

To examine this, Othayoth made an obstacle course of “beams,” or tall, bendable plates fitted on springs, to mimic flexible blades of grass, and monitored how cockroaches shifted between two kinds of 3D movements to go past the beams.

The two movements of the cockroaches were a “pitch,” or when they pitched up their body to press against the beams until they bent well to provide a way, which is strenuous, and a “roll,” when the cockroaches coiled into the gap between the beams to slide through, which is simpler.

The team digitally rebuilt the 3D motions of the cockroaches and beams to observe how the roll and pitch movements looked like on a potential energy landscape, which is a map that demonstrates how the complete potential energy of the animal and beams varies as the animal’s body shift towards the beams and rotates.

This map explains the joint impact of gravity and the elastic bending forces of the beams acting on the animal body, similar to an electric field or gravity field that can explain forces acting on a point mass or charge.

The variation is that the animal is self-propelled and encounters extra damping and frictional forces, adding to the ensuing complexity of motion.

This energy landscape showed that moving from a pitch to a roll movement is shifting from one energy “basin” to another on the landscape.

Imagine you have a bowl and put a marble in it. That marble will go to the bottom of the bowl where it’s most stable. Each time a cockroach did a movement, they were pulled towards the bottom of the bowl. We found that each type of movement can be described by one such bowl.

Chen Li, Study Senior Author, Physicist, and Assistant Professor, Mechanical Engineering, Johns Hopkins University

Li added, “Now imagine you have two bowls. When the cockroach transitioned from a pitch to a roll movement, it was like they hopped from the bottom of one bowl to the bottom of the other bowl.”

This illustrates that to transition from one kind of movement to another, the insects must overcome the sides of the first bowl, or simply, they have sufficient energy to overcome the energy barrier.

The scientists identified that the jittering legs of the cockroach shook the body to provide it with sufficient energy to overcome the barrier from a more tough pitch to a simpler roll movement, enabling traversal.

Also, the researchers constructed a robot to simulate the behavior of cockroaches and further altered the extent to which it jittered. The extent of the jitter was directly proportional to the energy the cockroach had to beat the energy barrier to transition from forcing across the beams to rolling into the gap to traverse.

These outcomes elucidate why legged robots that jitter much (like RHex, a six-legged robot that has been used for 10 years and can generally be seen in popular media) is fascinatingly expert at traversing huge obstacles, even without making use of any sensors or careful motion planning.

Li stated, “This strategy of ‘just shake yourself’ is the most naïve way to make transition, though. The animals can—and robots should—add more careful, active adjustments to do it better. That is what we are looking into as the next step.”

Li and his team stated that this new method of energy landscapes elucidates how animals utilize physical interaction to transition between various kinds of movements, and will guide robots to better traverse complex 3D terrain such as earthquake rubble.

According to Samuel Stanton, program manager, Army Research Office, an element of the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory, “If successful, the framework being developed by Professor Li’s team will be a leap ahead in our ability to realize fast and robust robots capable of deftly negotiating cluttered terrain.”

This study was funded by the Army Research Office, a Burrough Wellcome Fund Career Award at the Scientific Interface, an Arnold & Mabel Beckman Foundation Beckman Young Investigator Award, and The Johns Hopkins University Whiting School of Engineering start-up funds.