Brainless bristlebots found to exhibit swarming behavior

March 15, 2013 by Bob Yirka, weblog

(a) A collection of the BBots used in the experiment. (b) Schematic of an individual BBot. A plastic chassis is connected to a pair of toothbrushes via a slanted wedge. An eccentric motor is positioned on the top side of the device and is powered by a VARTA rechargeable button-cell battery. Credit: L. Giomi et al, arXiv:1302.5952
( —A robot research team at Harvard University has found that tiny robots that move by vibrating bristle strands when grouped together, form spontaneously into groups—exhibiting, what the team describes as swarming behavior. In their paper the team has uploaded to the preprint server arXiv, the group describes how they built tiny robots out of tiny vibrating motors, a battery and bristles and then allowed them to roam randomly, and found that once a certain number were placed in a confined space, they grouped together forming what looked like a swarm.

Swarming in the natural world has been studied for years by scientists trying to understand how a school of fish can all turn as one, for example, or how seemingly simple-minded can build complex nests. In the lab, robot researchers have built tiny bots (with tiny processor brains) that are able to exhibit some of the same behaviors as the real life organisms they are meant to copy, but they have sensors onboard. Now, in this new effort, the team of researchers has found that some degree of swarming can occur without its members having any sort of sensing ability or intelligence at all.

They built little robots out of , a pager vibrator motor, a small frame and a battery—no , processing chips or anything else that could be construed as providing intelligence or feedback sensing. When one of the robots is placed on a and turned on, it, it can move courtesy of the bristles, they are angled—when vibrating they push the bot forward. The team built two types of the bots, one kind simply moves around in a spinning motion, the other moves directly forward. When the bristlebots, as the team calls them, are placed together in a confined space, they run into each other and wind up moving around in chaotic fashion. But when more are added, they reach some tipping point and begin to bunch up, forming a crowd, or in this case, what the researchers call a swarm. Sometimes the swarm remains where it is, sometimes it moves, and sometimes those on the periphery leave and come back later to join the swarm again—all behavior that happens due to the properties of the bristle-bots themselves, working in apparent random fashion. Why they bunch, has yet to be explained.

Explore further: Tiny robot swarm able to play tunes on a virtual piano (w/ video)

More information: Swarming, swirling and stasis in sequestered bristle-bots, arXiv:1302.5952 [cond-mat.soft]

The collective ability of organisms to move coherently in space and time is ubiquitous in any group of autonomous agents that can move and sense each other and the environment. Here we investigate the origin of collective motion and its loss using macroscopic self-propelled Bristle-Bots, simple automata made from a toothbrush and powered by an onboard cell phone vibrator-motor, that can sense each other through shape-dependent local interactions, and can also sense the environment non-locally via the effects of confinement and substrate topography. We show that when Bristle-Bots are confined to a limited arena with a soft boundary, increasing the density drives a transition from a disordered and uncoordinated motion to organized collective motion either as a swirling cluster or a collective dynamical stasis. This transition is regulated by a single parameter, the relative magnitude of spinning and walking in a single automaton. We explain this using quantitative experiments and simulations that emphasize the role of the agent shape, environment, and confinement via boundaries. Our study shows how the behavioral repertoire of these physically interacting automatons controlled by one parameter translates into the mechanical intelligence of swarms.

via IEEE

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1 / 5 (6) Mar 15, 2013
Magnetic fields produced by the motors might be why they swarm?
3 / 5 (8) Mar 15, 2013
Coherent behavior in physics, biological systems, the Brazil nut effect and vibrating bristlebots all derive their coherence from a similar rule: Art Winfree's law of coupled oscillators, a mathematical principle which he posited in 1967 and then applied in the field of biology (heart cells, Malaysian fireflies, gaits of a horse). Steve Strogatz (Sync) extended Art's work.

Here's the principle: limit cycle oscillators have a tendency to coordinate their oscillations, and when they do, certain precise patterns identified by Winfree will emerge, and no others. Similar units, vibrating at a similar frequency, in proximity to each other, will synchronize in a specific Winfree pattern. These bristlebots are all identical, even as to the frequency at which their bristles oscillate. Bingo.

For an interesting and "unexpected" instance, read "Seeing quantum mechanics with the naked eye," PhysOrg Jan 9, 2012 (Cambridge experiment--polaritons). See also many other Macksb posts in PhysOrg.
3 / 5 (8) Mar 15, 2013
In this Harvard experiment, the "spinners" have a second periodic oscillation--their spin. Again, the bristlebots have similar spin properties, including specifically the frequency of the spin. So they will synchronize their spin oscillations.

Many other coherent behaviors, including swarms, follow Winfree's law. The Millenium Bridge problem in London (pedestrian legs "swarm" in response to bridge oscillations); flocks of starlings (coherence derived prob. from wing oscillations and proven fact that such birds track approx. 7 neighboring birds in a specific way--see Italian research in last few years); schools of minnows (same as birds, but relevant oscillations are their body oscillations used to swim); magnetism in all forms, including helimagnetism; perhaps Kepler's law; and spin-orbit coupling of moon to earth.

And more: all phases of matter and phase transitions (solid, liquid, gas, superfluid, superconductivity), which tie to temperature (frequency) and pressure (proximity).
1 / 5 (8) Mar 15, 2013
stupidest thing in years.
i better study my crap.
2.7 / 5 (9) Mar 15, 2013
Erm - that behavior does not look like it is so miraculous.
It's reduction of degrees of freedom due to the shape of the bot. Make circular bots and you won't see any swarming at all, as side-by-side bots on the rim will not prevent each other from turning and going off again.
1.8 / 5 (5) Mar 15, 2013
I agree in part, antialias, but disagree as to the larger picture.

Yes, circular bots will behave differently. But they are also likely to self-organize ("swarm") in some manner arising from Winfree's engine (oscillations) and his emergent control system: the need to integrate the oscillating units that give rise to oscillations that affect their neighbors. The resulting Winfree pattern will be constrained by various factors, such as the shape of the oscillators (here, the bots) and the particularities of the space in which the oscillators are confined.

Circular bots will probably spin (an oscillation) and coordinate their collective spins in a particular Winfree pattern. For a fun example, see "Physicists learn how to make bearings more stable," in PhysOrg just a few weeks ago--Feb 25, 2013.

Circles have an important invariance (rotational) that corresponds to the relevant periodic oscillation (the spin that I believe will result from a circular bot.
2 / 5 (4) Mar 15, 2013
A tendency for mindless things to 'swarm' can arise from acoustic interference patterns set up in a non-linear elastic media by two or more real or virtual sources of oscillation. This is what causes oscillators to couple and lock. Faraday waves arise similarly, as do the patterns produced by Chladni plates. In the case of the bristle bots- they are all operating at similar frequencies and working against a common surface. They all have the same basic elastic couplings, too. Like Anti, I don't think this all that unusual. Come to think of it, my brother had a vibrating football game where the players were passive components- much like the bristle bots but driven by the environment (vibrating sheet metal playing field.) As I recall, they had a tendency to swarm, too.
2.7 / 5 (7) Mar 15, 2013
What we're seeing is random motion that is constrained in a non-isotropic way. Which, as of necessity, will lead to aligned motion over time by the simple fact that it affects the probability distribution of the directions of a bot. (You can do a simler experiment at home by simply shaking a bag of non-spherical seeds once)

Round bots would produce occasional clumping, but not swarming (the clumping is due to the constraint of the arena). But I see no osillations going on here which transmit beyond the individual bot (which is what is necessary for a Winfree motion)
1 / 5 (3) Mar 15, 2013
As far I did see the video, I did see only, that the bristlebots are packed against the wall, which is nothing strange, if we consider the curvature of the wall. No signs of collective behavior at free space.
5 / 5 (8) Mar 15, 2013
The first thing I thought of when I read this article was the electric football games back in the 1970's. Vibrating "football field" with little football players set on bases with 4 little plastic whiskers underneath. I got bored playing it because the little football guys jammed together in tight little bunches more than anything else. I could bend the whiskers and make the players go in circles, or arcs, or even straight lines if I was patient enough and sufficiently bored to mess around with it.

The headline should read: "Researchers devise modern version of electric football - guys still jam together."

Here is what I'm talking about:
1 / 5 (2) Mar 15, 2013
Cool. But the experimenters have seriously violated Occam's Razor by even imagining that the robots could think. Heck, they have no nervous systems! It appears the researchers are not familiar with Winfree.
2.6 / 5 (5) Mar 15, 2013
Cool. But the experimenters have seriously violated Occam's Razor by even imagining that the robots could think. Heck, they have no nervous systems! It appears the researchers are not familiar with Winfree.

I'm thinking that was what the kiddos up at Harvard were doing. Showing that some of the "swarming" behaviors found in nature, may be influenced by non-biological means,,,

That shape, group density, medium and boundaries may have a larger influence on swarm behavior than "biological mechanisms" which are more complicated and convoluted than the simple, obvious cause.

But I could be reading the experiment wrong. Any thoughts?
2.1 / 5 (7) Mar 15, 2013
One could extrapolite this to an extreme: make very long, thin robots (think of robots shaped like a piece of notebook paper standing upright on its longest side.)

Seems to me that that as soon as two such bots meet they would align (and wouldn't be able to move away fom each other as any way one tries to turn that turning move would be blocked by the body of the other).
As soon as you have two such robots moving together any further single robot meeting up with them wouldn't be able to push them away - and hence be forced to align with them.

The 'swarm' could only grow from there.
5 / 5 (2) Mar 15, 2013
Was surprised they did not try mixing the two types to see what happens.
1 / 5 (2) Mar 16, 2013
When two bristlebots collide their moving directions change and they tend to rotate around each other, this where the third frequency/tertiary frequency comes in in addition of the frequencies of vibrating motors and spinning of bristlebots. This TF (the "third frequency") may be affected by shape, angle of collision, density of bristlebots . . . etc. The radii of these rotations would eventually interfere other neighbouring circular trajectories, when the density is sufficiently large and distance of confinement is small.

1 / 5 (3) Mar 16, 2013
(. . . continue)

The inelastic boundaries are non-vibrating and stationary special bristlebots with different shape, therefore, those ordinary bristlebots would tend to rotate around the boundaries too, with different TFs. I guess that bristlebots with higher third frequencies translate energy to those with lower TFs. I guess that the resonance of TFs would decrease the average/total energy of the system this where swarming emerges. Similar to the effect of friction between solid with relatively rough surface, locking of microstructures between two moving solids dissipates kinetic energy, bristlebots with circular shape still tend to swarming because of slight friction on surface. I speculate bristlebots coated with frictional material are with better swarming than those coated with smooth surface. And the aspect of the friction of the boundaries too. The stronger the friction the much the reducing on the tangential velocity which is better for the effect of swarming.

1 / 5 (3) Mar 16, 2013
I'd hazard a guess: The tiny entities moved randomly until encountering another at which time their several surface tensions became one.... and so on.
1.6 / 5 (10) Mar 16, 2013
I think it's funny how the video compares natural flocking behavior (systems which incorprate virtually infinite 6 degrees of freedom, and individual freedom of choice) with this two-dimensional, confined, and constrained system.

Even in two dimensions, it's obvious that the removal of the barrier would result in complete chaos. This is nothing more than order of confinement (think: sardines in a can).

But I do think it's funny the way this reminds me of those old football boardgames with the vibrating boards.

Seriously, haven't Harvard research teams anything better to do than to reinvent "Electric Football?"

5 / 5 (3) Mar 16, 2013
@ubavontuba: I agree with you. "Electric Footbal" sound like a perfect description this observation. I keep wanting to say Duhhh.
5 / 5 (1) Mar 16, 2013
Seems more like "clumping behavior".
2.6 / 5 (10) Mar 16, 2013
Looks like they actually constructed those 'robots'. I wonder how much tax payers money was wasted doing that. They could have just thrown some hair brushes onto a cloths drying machine (j/k).
Lobo Tommy
1 / 5 (3) Mar 16, 2013
Could this be some kind of surface tension in granular systems?
5 / 5 (4) Mar 16, 2013
I think using the term "swarming" is misleading. This is not like biological swarming. It is simply self-assembly or self-organization and is more similar to crystal formation. It is also well-known that randomly moving objects that are confined at high enough density will jam and often pack into an ordered structure that depends on their individual shapes. The work is definitely interesting, but the terminology is a little careless.
Whydening Gyre
1 / 5 (7) Mar 17, 2013
Think fluid mechanics.
not rated yet Mar 17, 2013
Conclusions here are totally bogus. What is called "swarming" is simply caused by the slight lifting caused by contact between two brushbots. This lifting causes the outside brush sets to become more powerful, push the 2 brushbots together, and keeps them there. That's all it is, folks.
1.7 / 5 (6) Mar 17, 2013
Any thoughts?
The self-organizing behavior is rooted in the Mandelbrot-like process of the fractal expression that is creation. Everything that exists is in symbiosis with that sort of process in some form or other. Self-assembling, evolving systems cannot continue to do so from randomness if they are not connected.
not rated yet Mar 18, 2013

yeah i thought he was gonna blow my mind by putting both locomotive patterns in the test space and illustrating the "swarm" behavior
not rated yet Mar 18, 2013
If they are all built the same it stands to reason they will behave the same when placed in the same environments, and placed in similar groups... As in move in the same direction, and "collect" in the same locations... there is no magic here or nothing that is unexplained or even anything that required a paper to describe it.
2.3 / 5 (3) Mar 18, 2013
A thorough example of erroneous conclusions proposed in a frail attempt to legitimize a frivolous expenditure of funds. Are these physics students or more likely poli sci? Either way, a government job awaits....
Whydening Gyre
1 / 5 (6) Mar 20, 2013
I'm thinking that was what the kiddos up at Harvard were doing. Showing that some of the "swarming" behaviors found in nature, may be influenced by non-biological means,,,

That shape, group density, medium and boundaries may have a larger influence on swarm behavior than "biological mechanisms" which are more complicated and convoluted than the simple, obvious cause.

But I could be reading the experiment wrong. Any thoughts?

Doubtful that you read it wrong. Came to the same conclusion. To my unlettered eye, this appears to be much more controlled modeling of brownian motion - with a lot fewer "atoms" and a much more severe space constraint. And.. could this be applied to a sociological aspect, perhaps?
1 / 5 (5) Mar 20, 2013
I do fully support the idea, that the "intelligent" swarming effects of multiparticle systems have the cause in their environment in the same way, like in the object itself. The Couder's replications of quantum phenomena at the water surface illustrate quite well the deBroglie wave concept and demonstrate the importance of the "wake ripples" around particles for their collective behavior.

Unfortunately, the experiment with bristlebots seems quite inconclusive in this matter. The bristlebots are lacking the apparent elastic environment, which would make their behavior cohesive in similar way, like at the case of particles in vacuum and/or Cooper pairs of electrons at the phonon field of superconductors. Everything what I can see at the MIT videos is their crowding against curved wall.

So that whereas the underlying idea is quite relevant, its experimental demonstration seems rather fringe for me.

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