World’s smallest self-powered bipedal robot achieves record speed and agility with simple mechanical design

At less than one and a half inches tall, roughly the same height as a LEGO minifigure, the world’s smallest self-contained bipedal robot can self-start from standstill, walk faster than a half mile per hour, turn, skip, and ascend small steps with just the power of its on-board battery, actuator, and control system.

The robot, more affectionately known as “Zippy” by its creators, is the latest output of a project led by Aaron Johnson and Sarah Bergbreiter at Carnegie Mellon University. The project is aimed at understanding locomotion at small scales in order to build more capable miniature walking robots.

“In a world designed for humans, two-legged robots are able to navigate uneven terrains and maneuver around objects more easily than robots with wheels,” explained Johnson, a professor of mechanical engineering. “For this reason, we have been investigating how to eliminate complex walking mechanisms to make simple, two-legged robots possible.”

Steven Man, one of the lead authors of this research to be presented at the IEEE International Conference on Robotics and Automation this year, emphasized the complexity, and importance, of miniature, legged robots.

“They can go into tight spaces that people and even other robots cannot manage. Zippy could be a resource for emergency search and rescue, industrial inspection, and even deployment to geologically interesting areas for scientific research,” he said.

Undergraduate students Soma Narita and Josef Macera were also lead authors on this work and helped to design Zippy based on the team’s prior steerable bipedal robot, Mugatu, that featured rounded feet and a single actuator at the hip.

The biped walks by lifting its front leg and shifting its center of gravity forward. The momentum from this shift, in combination with its rounded front foot, creates enough space for Zippy’s other leg to swing through and take a full step. Because of its small size, Zippy uses an additional mechanical hard stop to act as a joint limit for its hip instead of a servo.

“Both Zippy’s small size and our mechanical adjustments enable Zippy to walk at an incredible 10 leg lengths per second, which would be equivalent to an average adult moving at 19 miles per hour. This makes Zippy not just the smallest, but the fastest power-autonomous bipedal robot of any size by that metric,” said Bergbreiter, a professor of mechanical engineering.

Moving forward, the team plans to add sensors like cameras to Zippy so that it can localize and autonomously navigate environments. With localization capabilities, multiple robots could be deployed together to coordinate as a swarm for inspection or search and rescue operations in hazardous environments.