Surprisingly simple scheme for self-assembling robots

Oct 04, 2013 by Larry Hardesty
A prototype of a new modular robot, with its innards exposed and its flywheel — which gives it the ability to move independently — pulled out. Credit: M. SCOTT BRAUER

In 2011, when an MIT senior named John Romanishin proposed a new design for modular robots to his robotics professor, Daniela Rus, she said, "That can't be done."

Two years later, Rus showed her colleague Hod Lipson, a robotics researcher at Cornell University, a video of prototype robots, based on Romanishin's design, in action. "That can't be done," Lipson said.

In November, Romanishin—now a research scientist in MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL)—Rus, and postdoc Kyle Gilpin will establish once and for all that it can be done, when they present a paper describing their new robots at the IEEE/RSJ International Conference on Intelligent Robots and Systems.

Known as M-Blocks, the robots are cubes with no external moving parts. Nonetheless, they're able to climb over and around one another, leap through the air, roll across the ground, and even move while suspended upside down from metallic surfaces.

Inside each M-Block is a flywheel that can reach speeds of 20,000 revolutions per minute; when the flywheel is braked, it imparts its angular momentum to the cube. On each edge of an M-Block, and on every face, are cleverly arranged permanent magnets that allow any two cubes to attach to each other.

"It's one of these things that the [modular-robotics] community has been trying to do for a long time," says Rus, a professor of electrical engineering and computer science and director of CSAIL. "We just needed a creative insight and somebody who was passionate enough to keep coming at it—despite being discouraged."

Embodied abstraction

As Rus explains, researchers studying reconfigurable robots have long used an abstraction called the sliding-cube model. In this model, if two cubes are face to face, one of them can slide up the side of the other and, without changing orientation, slide across its top.

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The sliding-cube model simplifies the development of self-assembly algorithms, but the robots that implement them tend to be much more complex devices. Rus' group, for instance, previously developed a modular robot called the Molecule, which consisted of two cubes connected by an angled bar and had 18 separate motors. "We were quite proud of it at the time," Rus says.

According to Gilpin, existing modular-robot systems are also "statically stable," meaning that "you can pause the motion at any point, and they'll stay where they are." What enabled the MIT researchers to drastically simplify their robots' design was giving up on the principle of static stability.

"There's a point in time when the cube is essentially flying through the air," Gilpin says. "And you are depending on the magnets to bring it into alignment when it lands. That's something that's totally unique to this system."

That's also what made Rus skeptical about Romanishin's initial proposal. "I asked him build a prototype," Rus says. "Then I said, 'OK, maybe I was wrong.'"

Sticking the landing

To compensate for its static instability, the researchers' robot relies on some ingenious engineering. On each edge of a cube are two cylindrical magnets, mounted like rolling pins. When two cubes approach each other, the magnets naturally rotate, so that north poles align with south, and vice versa. Any face of any cube can thus attach to any face of any other.

The cubes' edges are also beveled, so when two cubes are face to face, there's a slight gap between their magnets. When one cube begins to flip on top of another, the bevels, and thus the magnets, touch. The connection between the cubes becomes much stronger, anchoring the pivot. On each face of a cube are four more pairs of smaller magnets, arranged symmetrically, which help snap a moving cube into place when it lands on top of another.

As with any modular- system, the hope is that the modules can be miniaturized: the ultimate aim of most such research is hordes of swarming microbots that can self-assemble, like the "liquid steel" androids in the movie "Terminator II." And the simplicity of the cubes' design makes miniaturization promising.

But the researchers believe that a more refined version of their system could prove useful even at something like its current scale. Armies of mobile cubes could temporarily repair bridges or buildings during emergencies, or raise and reconfigure scaffolding for building projects. They could assemble into different types of furniture or heavy equipment as needed. And they could swarm into environments hostile or inaccessible to humans, diagnose problems, and reorganize themselves to provide solutions.

Strength in diversity

The researchers also imagine that among the mobile cubes could be special-purpose cubes, containing cameras, or lights, or battery packs, or other equipment, which the mobile cubes could transport. "In the vast majority of other modular systems, an individual module cannot move on its own," Gilpin says. "If you drop one of these along the way, or something goes wrong, it can rejoin the group, no problem."

"It's one of those things that you kick yourself for not thinking of," Cornell's Lipson says. "It's a low-tech solution to a problem that people have been trying to solve with extraordinarily high-tech approaches."

"What they did that was very interesting is they showed several modes of locomotion," Lipson adds. "Not just one cube flipping around, but multiple cubes working together, multiple cubes moving other cubes—a lot of other modes of motion that really open the door to many, many applications, much beyond what people usually consider when they talk about self-assembly. They rarely think about parts dragging other parts—this kind of cooperative group behavior."

In ongoing work, the MIT researchers are building an army of 100 cubes, each of which can move in any direction, and designing algorithms to guide them. "We want hundreds of cubes, scattered randomly across the floor, to be able to identify each other, coalesce, and autonomously transform into a chair, or a ladder, or a desk, on demand," Romanishin says.

Explore further: Programmable glue made of DNA directs tiny gel bricks to self-assemble

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grondilu
3 / 5 (3) Oct 04, 2013
" As with any modular-robot system, the hope is that the modules can be miniaturized: the ultimate aim of most such research is hordes of swarming microbots that can self-assemble, like the "liquid steel" androids in the movie "Terminator II." And the simplicity of the cubes' design makes miniaturization promising. "

Great. We're doomed.
QuixoteJ
1.7 / 5 (10) Oct 04, 2013
Great. We're doomed.
I second that!
But the concept for joining cube faces with cyclindrical rotating magnetic edges is positively ingenious.
Kedas
1.5 / 5 (10) Oct 04, 2013
I knew The Borg is scary but I didn't know we came up with the design.
MikeBowler
1 / 5 (1) Oct 04, 2013
what sort of things can something like this be used for?
Jeffhans1
5 / 5 (4) Oct 04, 2013
Build with ability to be wireless powered. Use in space.
krundoloss
2.2 / 5 (12) Oct 04, 2013
Im just happy that Mr. Romanishin kept on following his passion, ignoring his professor's doubts and exceeding expectations. And I skoff at the professor, why would he discourage his student from trying something new and innovative? Teachers should always encourage their students!

I used to watch Star Trek, and I always wondered how they could combine technologies they already had to do more. Now it seems in this modern world we have much technology that can be combined in new and interesting ways. The method of locomotion that was designed for these cubes is such a technology, all the parts were available, it was just up to Mr. Romanishin to combine them in the right way.
NeutronicallyRepulsive
2.7 / 5 (7) Oct 04, 2013
There is one quotation that fits perfectly here, I think:

"You Maniacs! You did it! Ah, damn you! God damn you all to hell!"
Captain Stumpy
1.6 / 5 (10) Oct 04, 2013
"There's a point in time when the cube is essentially flying through the air," Gilpin says. "And you are depending on the magnets to bring it into alignment when it lands. That's something that's totally unique to this system."

That's also what made Rus skeptical about Romanishin's initial proposal. "I asked him build a prototype," Rus says. "Then I said, 'OK, maybe I was wrong.'"


it is good to see an educator admit to being wrong... I've met so many who could not, even in the face of overwhelming evidence. this is a good educator.
Neinsense99
1.5 / 5 (6) Oct 04, 2013
I knew The Borg is scary but I didn't know we came up with the design.

Borg? Hmmm.... Imagine the happiness of teenage boys If they could self-assemble Geri Ryan....http://www.wallcg...r-25046/
AdamCC
3.3 / 5 (3) Oct 05, 2013
Build with ability to be wireless powered. Use in space.


Brilliant! Put solar panel on one or more face, and possibly some inductive charging (go to base station for a recharge) ...
MRBlizzard
1 / 5 (5) Oct 07, 2013

http://www.wallcg...r-25046/

Symantec blocked attack by

Neutrino Exploit Webkit? 4
antialias_physorg
1 / 5 (1) Oct 07, 2013
Build with ability to be wireless powered. Use in space

Unfortunately it doesn't work in space - as these flywheels need something to push off of. They'd just spin around their axes in space. (The modular self assembly trick is very relevant, though)

The general concept of self assembly into different structures as needed is certainly something that is interesting for groundside exploration. (e.g. on Mars or the moons of Jupiter/Saturn)
TheGhostofOtto1923
1 / 5 (3) Oct 07, 2013
Build with ability to be wireless powered. Use in space

Unfortunately it doesn't work in space - as these flywheels need something to push off of. They'd just spin around their axes in space. (The modular self assembly trick is very relevant, though)
-Unbelievable.

"Next-Generation Manned Maneuvering System with Control-Moment Gyroscopes for Extravehicular Activities Near Low-Gravity Objects"

-George clooney can be seen riding one in 'Gravity'.

Gyros are routinely used in space. Remember when the astronauts replaced them in the Hubble? Guess not.

Another embarrassing guess by a software engr. You guys do know you're not real engrs right?
antialias_physorg
3 / 5 (4) Oct 07, 2013
-Unbelievable.

Yep. Unbelievable. Gyros are ATTITUDE control ONLY.
Another embarrassing guess by a software engr.

Yep. It's basic physics, m'boy. You fail.
TheGhostofOtto1923
1 / 5 (2) Oct 07, 2013
Yep. Unbelievable. Gyros are ATTITUDE control ONLY.
-which is exactly what they are used for in the cubes. And MMUs.

"A control momentum gyroscope (CMG) is an attitude control device generally used in spacecraft attitude control systems. A CMG consists of a spinning rotor and one or more motorized gimbals that tilt the rotor's angular momentum. As the rotor tilts, the changing angular momentum causes a gyroscopic torque that rotates the spacecraft."

-Translation for pseudo-engineers: gyros provide 'something to push off of' so that things in space can adjust and maintain their attitude. Including gadgets like these cubes.

"The proposed design of a next-generation maneuvering and stability system incorporates control concepts optimized to support astronaut tasks and adds control-moment gyroscopes (CMGs) to the current Jetpack system...the forces and torques on an astronaut can be significantly reduced with the new control system actuation while conserving onboard fuel."
TheGhostofOtto1923
1 / 5 (2) Oct 07, 2013
"Ein Kreiselinstrument oder Gyroskop (gr. γύρος gyros "Drehung" und σκοπεῖν skopein, sehen,) ist ein rasch rotierender, symmetrischer Kreisel, der sich in einem beweglichen Lager dreht. Das Lager kann eine kardanische Aufhängung sein oder ein Rahmen in Form eines Käfigs (siehe Abbildung). Aufgrund der Drehimpulserhaltung weist der Kreisel ein hohes Beharrungsvermögen gegenüber Lageänderungen im Raum auf. Wird die Drehgeschwindigkeit zwischen Kreisel und Käfig gemessen, spricht man von einem Gyrometer." Und so weiter.

"Unter einem gyroskopischen Effekt versteht man einen Selbststeuerungseffekt, der einem System aufgrund der Drehbewegung einzelner Elemente oder des gesamten Systems innewohnend (inhärent) ist. Dabei handelt es sich nicht nur um eine Stabilisierung aufgrund des Trägheitsmoments, sondern auch um dynamische Vorgänge, die das System auch bei Störungen in einen stabilen Zustand zurückführen können."

-Seltsam, oder?
antialias_physorg
3 / 5 (2) Oct 08, 2013
which is exactly what they are used for in the cubes. And MMUs.

No. If you watch the video they use it for motion (even jumping). The connection (and movement of the blocks once they are in contact) is via magnets. The magnet part is completely sufficient for space. The gyro part is not needed*.

(*One could add a few specialized gyro-cubes to orient an entire structure amde uop of many, many cubes. But a gyro per cube is complete overkill in space)

The crucial part of the article is this:
"If you drop one of these along the way, or something goes wrong, it can rejoin the group, no problem."

But this works ONLY in a gravity field (with some ground to land on/push off of). In space this doesn't work.
antialias_physorg
3.7 / 5 (3) Oct 08, 2013
which is exactly what they are used for in the cubes. And MMUs.

No. If you watch the video they use it for motion (even jumping). The connection (and movement of the blocks once they are in contact) is via magnets. The magnet part is completely sufficient for space. The gyro part is not needed*.

(*One could add a few specialized gyro-cubes to orient an entire structure amde uop of many, many cubes. But a gyro per cube is complete overkill in space)

The crucial part of the article is this:
"If you drop one of these along the way, or something goes wrong, it can rejoin the group, no problem."

But this works ONLY in a gravity field (with some ground to land on/push off of). In space this doesn't work.

-Seltsam, oder?

What's strange is that you don't even know the difference between momentum and angular momentum.
TheGhostofOtto1923
1 / 5 (2) Oct 10, 2013
they're able to climb over and around one another
This will be easier in microgravity.
modular-robot systems are also "statically stable," meaning that "you can pause the motion at any point, and they'll stay where they are
This will be easier in microgravity.
But this works ONLY in a gravity field (with some ground to land on/push off of). In space this doesn't work
Well of course not. You would need thrusters or tethers for this. But we were talking about attitude control, which by your comment:
They'd just spin around their axes in space
-it was obvious that you did not know, that gyros are routinely used for attitude control in microgravity. Even the sliding-cube model would work without gravity.

"...if two cubes are face to face, one of them can slide up the side of the other and, without changing orientation, slide across its top"

-Gyros would maintain orientation of both cubes during the process. These cubes could not do this in gravity.
TheGhostofOtto1923
1 / 5 (2) Oct 10, 2013
you don't even know the difference between momentum and angular momentum
Where have I given any indication that I dont know the difference between momentum and angular momentum?

Angular momentum is what sandra bullock has when she is whirling around on the end of the robot arm. Momentum is what sandra bullock has when she releases herself and goes flying off in space.
http://www.youtub...iKOy59o4

AAAH. AAAHH. AAAAHHHHHHHH.