The Open Source Robot of Theseus Trots Its Way Into Hands-On Experiments in Animal Locomotion

Researchers from the University of Michigan have developed an open source modular robotic testbed designed to experimentally investigate the evolutionary origins of animal locomotion: the Robot of Theseus (TROT).

"In paleontology, we can go back and look at bones, but it's really difficult to understand how these changes in limb proportion, or in range of motion, may have affected the way an animal can move," explains corresponding author Talia Moore of the team's work. "There have been some really great insights on this question from robots that each mimic one extinct animal very precisely, but each robot took years to design and construct. I wanted to make a robot that could easily shapeshift into several different extinct species proportions, so that we could compare them, and see how the evolution of those limb lengths and other features would affect their locomotion. With TROT, 60 million years of evolutionary changes in body size can happen in 20 minutes."

The robot, inspired by a 1794 experiment on running cheetahs and goats, is designed to be modular: built out of a combination of 3D-printed and off-the-shelf supplies for a cost of around $4,000 per unit, the robot's shape can be easily customized in order to model specific mammals — including extinct species — while its limbs use backdrivable motors for adjustable spring stiffness and motion range. Each limb can be switched between three or four rigid links, the direction of the femur-tibia joint can be adjusted to mimic a knee or elbow, and the limb links include a telescoping system for adjusting their length.

"Traditional robots are designed with an emphasis on industrial applications and are expensive to make. TROT was designed with ease of fabrication in mind," notes first author Karthik Urs of the robot. "The overall part count is kept low, and most of the parts only fit together one way. That means that scientists can make most of the robot parts in-house with commodity 3D printers, assemble them and get to experimenting faster. It also makes the iteration process quick—key to enabling exploration in both robot and experimental design."

The team's paper has been published in the journal Bioinspiration & Biomimetics under open-access terms, while the CAD models and 3D print files can be found on the University of Michigan Library's Deep Blue Data site under the Creative Commons Attribution-NoCommercial 4.0 license.