MIT’s HERMIT Crab Robots Can Do Anything You Shell Them To

Inspired by the shell-swapping hermit crab, MIT’s HERMITS use interchangeable mechanical shells to do all sorts of creative things

3 min read
MIT's hermit crab-inspired HERMITS robots
Photo: MIT

Robots are well known to be specialists, doing best when they’re designed for one very specific task without much of an expectation that they’ll do anything else. This is fine, as long as you’re OK with getting a new specialist robot every time you want something different done robotically. Making generalist robots is hard, but what’s less hard is enabling a generalist to easily adapt into different kinds of specialists, which we humans do all the time when we use tools.

While we’ve written about tool using robots in the past, roboticists at the MIT Media Lab have taken inspiration from the proud and noble hermit crab to design a robot that’s able to effortlessly transition from a total generalist to highly specialized and back again, simply by switching in and out of clever, custom made mechanical shells.

MIT Hermits MIT’s HERMITS combine small robotic cubes with mechanical shells. Image: Ken Nakagaki

HERMITS, which almost certainly does not stand for Highly Extendable Robotic Modular Interactive Toio Shells, even though I’m going to pretend that it does (#backronym), are based around Sony’s little Toio robots. We wrote about Toio a few years ago—they’re two-wheeled robotic cubes that can localize themselves based on infrared patterns in a special mat that they zip around on, allowing them to interact with each other and with other objects through a centralized controller. Toios are designed to be modified, but mostly just as toys, which apparently doesn’t take them anywhere close to their full potential.

Ken Nakagaki, a roboticist at the MIT Media Lab, made a minor modification to the Toio robots by adding a little servo motor that can poke a pin up out of the robot’s top. It’s just a small change, but it enables all kinds of new things, since it allows the robots to drive inside of custom shells and dock with them, just like a hermit crab. But unlike any hermit crab I’ve ever seen, these shells can be endowed with clever mechanical transmission systems that leverage the robots’ motors to give them highly specialized capabilities on-demand.

This concept is really cool— with just a few generalist mobile bases, you can make as many specialist shells as you want, most of which are passive without any kind of electronics inside, making them relatively easy to produce using a 3D printer. The HERMITS can then swap in and out of shells whenever they need to. You can scale up the system by adding more HERMITS if you want, but the important thing is that you’re investing in additional generalist capability, which is far more efficient than specialists which will just sit around not doing anything most of the time. 

mit hermits

mit hermits Future research directions for MIT’s HERMITS. Image: MIT

The researchers have been able to control up to 70 robots at once, using 14 Raspberry Pis, which is perhaps not the most streamlined approach but definitely reinforces how fundamentally low cost and accessible the HERMITS system is. At the same time, there’s a massive amount of future potential, as shown in the figure above, from new form factors to fabrication and assembly to shells with more sophisticated embedded mechanisms. There’s way more detail on the HERMITS website, and if you want a Toio of your own, you can find a kit online for about $270.

HERMITS: Dynamically Reconfiguring the Interactivity of Self-Propelled TUIs with Mechanical Shell Add-ons, by Ken Nakagaki, Joanne Leong, Jordan L Tappa, João Wilbert, and Hiroshi Ishii from MIT, was presented at UIST 2020.

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Robot with threads near a fallen branch

RoMan, the Army Research Laboratory's robotic manipulator, considers the best way to grasp and move a tree branch at the Adelphi Laboratory Center, in Maryland.

Evan Ackerman

This article is part of our special report on AI, “The Great AI Reckoning.

"I should probably not be standing this close," I think to myself, as the robot slowly approaches a large tree branch on the floor in front of me. It's not the size of the branch that makes me nervous—it's that the robot is operating autonomously, and that while I know what it's supposed to do, I'm not entirely sure what it will do. If everything works the way the roboticists at the U.S. Army Research Laboratory (ARL) in Adelphi, Md., expect, the robot will identify the branch, grasp it, and drag it out of the way. These folks know what they're doing, but I've spent enough time around robots that I take a small step backwards anyway.

The robot, named RoMan, for Robotic Manipulator, is about the size of a large lawn mower, with a tracked base that helps it handle most kinds of terrain. At the front, it has a squat torso equipped with cameras and depth sensors, as well as a pair of arms that were harvested from a prototype disaster-response robot originally developed at NASA's Jet Propulsion Laboratory for a DARPA robotics competition. RoMan's job today is roadway clearing, a multistep task that ARL wants the robot to complete as autonomously as possible. Instead of instructing the robot to grasp specific objects in specific ways and move them to specific places, the operators tell RoMan to "go clear a path." It's then up to the robot to make all the decisions necessary to achieve that objective.

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