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.
Transcript
00:00:02 Here in the School of Physics at Georgia Tech, we're interested in how organisms manage to move around in complex environments. One component that allows animals to move so well is that they have limbs and legs, which can be multifunctional. They can allow the animal to climb over ledges. They can allow the animals to sprint rapidly over hard ground, to paddle through soft
00:00:23 ground, and even potentially kick through fluids. So we're interested in exploring how uh limbs can enable robots to move around with the agility and mobility that some animals with limbs have. The idea is to begin to develop a terodamics equivalent to arrow and hydrodnamics which will allow us to predict mobility of devices in these complex environments. The robot that we
00:00:45 created uh is based on a simple toy robot and then we took its legs off and replaced those with legs that we 3D printed. And we found that legs with a positive curvature such that the open part of a sea is pointing upward uh worked on average better than legs with a negative curvature producing more thrust force as well as more lift force. We took these force relationships that
00:01:08 we measured and we input them into a special kind of simulation called a multi-body dynamic simulation. We found that when we put the force relationships into the simulation, we could predict the robot speed to a few percent over a pretty wide range of conditions of leg geometry and and granular material. We think that for roboticists and engineers who are interested to design
00:01:33 vehicles that can move on loose granular material, they can immediately begin to optimize limb shapes and limb trajectories of small robots. In a real search and rescue robot, the type of terrain that this robot will encounter is not even necessarily granular material. But we think that one component could be the type of loose material which robots are stymied on and
00:01:58 which animals can often navigate so well. And we think that this kind of terodnamics of granular material will allow design of devices with better performance than what's currently available.
