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“Terradynamics” Predicts How Robots Will Move on Granular Surfaces

Using a combination of theory and experiment, researchers have developed a new approach for understanding and predicting how small legged robots – and potentially also animals – move on and interact with complex granular materials such as sand.

The research could help create and advance the field of “terradynamics” – the science of legged animals and vehicles moving on granular and other complex surfaces. Providing equations to describe and predict this type of movement – comparable to what has been done to predict the motion of animals and vehicles through the air or water – could allow designers to optimize legged robots operating in complex environments for search-and-rescue missions, space exploration or other tasks.

Robots such as the Mars Rover have depended on wheels for moving in complex environments such as sand and rocky terrain. Robots envisioned for autonomous search-and-rescue missions also rely on wheels, but as the vehicles become smaller, designers may need to examine alternative means of locomotion.

The researchers examined the motion of a small, legged robot as it moved on granular media. Using a 3D printer, they created legs in a variety of shapes and used them to study how different configurations affected the robot’s speed along a track bed. They then measured granular force laws from experiments to predict forces on legs, and created simulation to predict the robot’s motion.

Beyond understanding the basic physics principles involved, the researchers also learned that convex legs made in the shape of the letter “C” worked better than other variations. The six-legged experimental robot was just 13 centimeters long and weighed about 150 grams. Robots of that size could be used in the future for search-and-rescue missions, or to scout out unknown environments such as the surface of Mars. They could also provide biologists with a better understanding of how animals such as sand lizards run and kangaroo rats hop on granular media.

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