Robots can flap wings like a bird, slither like snakes, and run like a cheetah. Some are designed to mimic turtles and fish. A group of roboticists in Spain decided to try another tack: moving with no limbs at all and no wheels, and having the robot be spherical. It’s called Rosphere.
It isn’t as crazy as it sounds. Rosphere doesn’t need to worry about rough terrain, because it can roll in any direction, where wheels have to turn. That also means soft terrain, like mud, is much easier to roll through, since a ball can’t dig in the way wheels do. And being shaped like a ball the robot can’t fall over.
To move, the researchers, led by Juan Hernández, took inspiration from hamster wheels. Hamsters — or people, if you get one big enough — can move around just by walking towards the side of the ball, which rolls in the same direction. So they built a system of pendulums to shift Rosphere’s center of mass. The pendulums can swing in two different directions, and they move weight around, so that as the pendulum swings to the right, the center of the ball’s mass is on the right. Since a ball, or anything else, tends to rest at a point where the center of mass is closest to the ground, the ball rolls until the weight is as low as it can go.
(If you want to demonstrate this, tape a piece of string to the top of a hamster ball and tie a sinker to the other end. The ball will rest in one of two ways: either the sinker is on the bottom of the ball, or it hangs from the top straight down. The second thing is much harder to do because if the ball swings the slightest bit, it will roll until the weight rests at the bottom).
The team tested Rosphere on a crop field, letting it roll around and monitor moisture levels in the air and soil. The robot was able to roll around and take measurements from a variety of places, and get around the fields relatively easily. They also tested it in a park, to see if it could get around people without causing any problems, such as running into them, and found that it could do that too (they did not say whether any wayward children mistook it for a soccer ball).