MIT develops small, energy-efficient one-legged hopping robot

Researchers at the Massachusetts Institute of Technology (MIT) have identified the hopping locomotion of robots as optimal for disaster search missions because the robots need to expend the least amount of energy to move. The MIT robot hops on just one leg in the laboratory and is only 5 cm tall.

The hopping locomotion of a robot with only one leg has many advantages: it does not require much energy, thus extending the useful life of the robot, and large obstacles and slopes can be easily jumped over. The alternative flying locomotion, on the other hand, is more energy-intensive. Robots with legs and wheels often require even more power.

Better energy efficiency

MIT’s hopping robot is only about 5 cm tall and weighs less than a gram. As soon as the robot jumps on one leg, it converts potential energy from its height above the ground into kinetic energy. On impact with the ground, it is converted back into potential energy and so on. This results in better energy efficiency.

In their study “Hybrid locomotion at the insect scale: Combined flying and jumping for enhanced efficiency and versatility”, published in Science Advances, the MIT researchers attempted to maximize this. To this end, the scientists equipped the robot’s elastic leg with an additional spring. This converts the robot’s downward speed into an upward speed as soon as it hits the ground.

“If you have an ideal spring, the robot can simply keep hopping without losing energy. But since our spring is not quite ideal, we use a flapping mechanism to compensate for the small amount of energy it loses when it hits the ground,” explains Yi-Hsuan Hsiao, MIT graduate student and researcher involved in the project. This is because the scientists have given the robot flapping wings. They are driven by soft, artificial muscles with little energy and provide additional lift during the upward movement to compensate for the lost energy. They also stabilize the robot in the air and align it for the next jump.

The hopping robot is controlled by a control mechanism that determines how the robot must be aligned for its next jump. An external motion tracking system and an observation algorithm use sensor measurements to calculate the information required to control the robot.

Flapping wings determine the flight path

At the apex of the flight path, the controller calculates the possible landing position, the necessary take-off speed for the next jump and controls the wings so that the robot lands on the ground at the correct angle and jumps off in the desired direction.

The researchers tested the robot on different surfaces such as grass, ice, wet glass and even uneven ground. The robot had no problems. Even on moving surfaces, it was able to jump stably – up to 20 cm.

However, jumping on grass requires more energy than jumping on glass surfaces because more energy has to be used for the wing beat to compensate for the damping effect of the grass. Compared to a flying robot, the hopping robot is said to require 60 percent less energy.

Depending on the programming, the MIT robot is also capable of acrobatic feats such as somersaults or jumping onto a flying drone. It can also carry twice its weight in payload. According to the scientists, this can be significantly increased. However, the spring in the robot’s leg must then be adjusted.

The MIT scientists now want to install sensors, batteries, and control electronics in the hopping robot. So far, it is still dependent on external control devices and only works in the laboratory. The researchers then want to release it from the lab into the wild, where it will hop around autonomously and help with rescue missions, for example.

(olb)