Planar Catoms

      Creating Motion without Moving Parts  

The self-actuating, cylinder-shaped planar catom tests concepts of motion, power distribution, data transfer and communication that will be eventually incorporated into ensembles of nano-scale robots.   It provides a testbed for the architecture of micro-electro-mechanical systems for self-actuation in modular robotic devices. Employing magnetic force to generate motion, its operations as a research instrument build a bridge to a scale of engineering that will make it possible to manufacture self-actuating nano-system devices.

The planar catom is approximately 45 times larger in diameter than the millimeter scale catom for which its work is a bigger-than-life prototype.   It operates on a two-dimensional plane in small groups of two to seven modules in order to allow researchers to understand how micro-electro-mechanical devices can move and communicate at a scale that humans cannot yet readily perceive -- or imagine.   It forms a bridge into this realm across the evolving design of a sophisticated electro-magnetic system whose features have followed a path of trail and error as the CMU-Intel Claytronics Research Team has tested the concept of a robot that moves without moving parts.  

In its brief history of demonstrating motion without moving parts, the planar catom has evolved through eight versions.   It began life as a concept vehicle engineered with catalog-sourced hardware.   It has become a custom-designed electronic and magnetic system that carries a complete control package aboard its module.  

Weighing 100 grams, Planar Catom V8, shown in the picture here, presents for view its stack of control and magnet-sensor rings.   Its solid state electronic controls ride at the top of the stack.   An individual control ring is dedicated to each of the two rings of magnet sensors, which ride at the base of the module.   Two thin threaded rods extend like lateral girders from top to bottom through the outside edge to brace the rings.   A central connector stack carries circuits between control and magnet rings, enabling easier handling and maintenance of components while also providing internal alignment and stability along the cylinder 's axis.

At the base of the planar catom, the two heavier electro-magnet rings, which comprise the motor for the device, also add stability.     To create motion, the magnet rings exchange the attraction and repulsion of electromagnetic force with magnet rings on adjacent catoms.   From this conversion of electrical to kinetic energy, the module achieves a turning motion to model the spherical rotation of millimeter-scale catoms.

Motion from Two Magnet Rings  

Pictured in a top view (left, below), two magnet rings from Planar Catom V7 display the arrangement of their 12 magnets around individual driver boards and the coil design for horseshoe magnets introduced with Version 6 and then upgraded in versions 7 and 8.  

 

The magnets are arranged in the containment ring as the straightedge faces of a 12-sided polygon seated in the acrylic plate that holds them in place.   The horseshoe magnets feature 39AWG magnet wire wrapped around AISI 1010 steel cores, components selected to balance machinable metal and flux-saturation density.  

Replacing barrel-shaped, round-face magnets in Planar Catom Versions 1-5, the horseshoe magnet was adopted to boost magnet strength and create a wider footprint.   It also represents an evolution of the use of flat-surface magnets, which were introduced in Planar Catom Version 5.   Flat surfaces prove to be more efficient for contact than round-face magnets. In a fully assembled catom, as seen in the earlier picture of the V8 (above, right), a second magnet ring would ride below each of these rings.   The faces of the lower rings would be offset to the 12 gaps that appear between the magnets in this top view.

This view also highlights the geometry of plane surface magnets as force effectors .   A catom sustains a clockwise or counterclockwise motion by a continuous transfer of electro-magnetic force to achieve the opposite motion in the other catom.

When compared to a stepper motor, another brushless, synchronous motor that relies upon a large number of steps to sustain motion, the planar catom faces unique issues from alignment and friction, which this image suggests.  

Imagine a third catom rotating in the space above the side-by-side rotation of these adjacent magnet rings.   Its magnets would contact magnets toward the top of the two magnet rings shown here because of the physical impossibility of its touching magnet faces nearer the point where these two exchange a contact.  

This configuration highlights the temporarily "orphan " character of magnets situated on either side of the contact points at any given moment in the rotation of adjacent catoms.   To better manage the flow of power in this circumstance where a contacting magnet blocks the potential of its neighbors, the controller operates each magnet ring as 3 independent groups of four magnets.   Thus it is possible to direct power to one magnet in a group of four as the rotation advances in an ensemble.  

This electrical design increases the accuracy of the alignment between catoms.   It improves torque control and heat management.   It also eliminates 18 unnecessary signal paths from an earlier architecture that allocated an independent signal path to each magnet.   This design to refine functionality represents a 30 percent reduction of circuit complexity.   It also illustrates the Ensemble Axiom 's influence as an overarching design criterion.   In this instance, it drives an economy of function to reduce complexity in the device.   Because there was no benefit for the ensemble in the capacity of four neighboring magnets to actuate simultaneously, the arrays of four magnets have been electronically consolidated to focus actuation on the most magnet in the group that comes closest to a neighboring catom.   This modification in design enhances the functionality for the ensemble while streamlining an element of the module 's complex alignment.  

Electronic Density for Device Control  

That economy in the design of the controls also makes more room for the rest of the robust package of electronics that operate the module.  

The picture to the right displays a planar catom controller ring with light emitting diodes (LEDs) arranged around its perimeter.   This board directs the two magnet driver boards embedded in the magnet rings, as shown in the image above.  

A more typical robotics servo controller would carry a microprocessor, motors, servos and other devices on one side of a 50 mm x 75 mm board embedded with two layers of microcircuits. While building planar catoms to investigate a customized actuation system that creates motion without moving parts, the design team also achieved the complementary objective of constructing a robust, self-contained modular robot.

In pursuing a goal that is broader than the testing of an individual system for a modular robot, the research team has gained experience with micro-electro-mechanical system (MEMS) interfaces that use "genderless " connectors while testing algorithms for the transfer of data and power across unary circuits whose points of connection occur in a transitory state because of the rotation of the modules across which the circuits are formed.   This is the essence of the challenge of constructing nanoscale devices whose motion will enable the shaping of 3-dimensional representations of objects from ensembles of thousands of catoms.

Another component of this robust electronic system is shown in the picture below of a Planar Catom Infrared Communication Board.  

On this device, the Infrared Data (IrDA) transmitters and receivers are separately multiplexed to transmit and receive signals on separate channels, allowing fast, simultaneous transmission on all channels.   These global communication features anticipate the necessity of debugging and reprogramming large ensembles of catoms.

The engineering goal for these components is a system that supports cooperative behavior among nanoscale robotic modules.   This concept of machine behavior is one in which the primary devices direct their own motion toward a common goal by employing functionality that focuses every element of design on the requirements of the ensemble rather than on those of the individual robot.   The engineering design thus adheres to the ensemble axiom by incorporating in these devices only those functions that advance the functionality of the ensemble.

In the present stage of development, this model of cooperative movement -- motion without moving parts -- can be seen in this video of two planar catoms exchanging electromagnetic force in order to develop a circular motion.

The flexibility of its electro-magnetic system also enables the planar catoms to emulate the shapes of hexagonal and cubic lattices, as well as various irregular polygonal configurations, which are relevant to the modelling of nano-scale catom ensembles.   These shapes conform to lattice configurations that optimize the communication among individual spherical catoms in an ensemble.   For example, within a fully-populated, three-dimensional hexagonally arranged ensemble, an individual catom would have direct contact with as many as 12 other catoms.

The hexagonal configuration of a group of planar catoms is highlighted in this concept video , which demonstrates the principle of motion without moving parts.   In the video, with an exchange of electromagnetic force one catom rotates against an ensemble of six other catoms, whose conductive nodes appear as small colored beads around the perimeter of each barrel-shaped module.

The feasibility of "motion without moving parts " is further explained in this article for the American Association of Artificial Intelligence .

To gain a close-up view of a planar catom 's electrical components and more detailed illustration of the evolution of the design and electro-magnetics of the planar catom, visit this page of   design notes .  

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