Q: Can we design robots that, when composed fractally, provide utility at multiple length scales?


What’s the big picture?

Robots deployed at orders of magnitude different size scales, and that retain the same desired behavior at any of those scales, would greatly expand the environments in which the robots could operate. However it is currently not known whether such robots exist, and, if they do, how to design them.

What’s new?

Since self similar structures in nature often exhibit self similar behavior at different scales, we hypothesize that there may exist robot designs that have the same property. In our paper we demonstrate that this is indeed the case for some, but not all, modular soft robots: there are robot designs that exhibit a desired behavior at a small size scale, and if copies of that robot are attached together to realize the same design at higher scales, those larger robots exhibit similar behavior. We show how to find such designs in simulation using an evolutionary algorithm.

Why fractals?

When fractal attachment is not assumed and attachment geometries must thus be evolved along with the design of the base robot unit, scale invariant behavior is not achieved, demonstrating that structural self similarity, when combined with appropriate designs, is a useful path to realizing scale invariant robot behavior.

What hardware was used?

We validate our findings by demonstrating successful transferal of self similar structure and behavior to pneumatically-controlled soft robots. We also show that biobots can spontaneously exhibit self similar attachment geometries, thereby suggesting that self similar behavior via self similar structure may be realizable across a wide range of robot platforms in future.

Where was the paper published?

The paper will appear July 12-16, 2021, in the proceedings of Robotics: Science and Systems (RSS). RSS is one of, if not the most prestigious robotics conference in the world, focusing more on risky but potentially paradigm shattering robot science than safe and incremental engineering improvements. Conference papers are peer reviewed by three experts in the field, only the best submissions are accepted to be presented at the conference and appear in the proceedings.

Can I evolve my own fractal robots?

Yes, please fork our source code.

Just show me some videos already!

Check out our videos and images, which you are free to use under a creative commons license.