<p> FlexM: computational hub-and-strut construction toy Camarata, Do, Eng, Gross, Weller</p><p>ABSTRACT devices, “Machine Readable Models” and “Intelligent Modeling Systems,” enabled designers to build models INTRODUCTION that interface with software that can give design advice. Construction toys such as Lego, Meccano, and TinkertoyDewey and Patera (1987) developed processors to gave many people a first experience with creativemanipulate the geometry of 3D models. All these projects, engineering design. These toys, at least in their originalhowever, lack a real-time interface for detecting moving “pure” forms, provided a limited set of elements thatpieces. Gorbet and Orth’s (1997) Triangles is a young designers could assemble to build a wide variety ofconstruction kit of flat, plastic triangles, that interface to a forms. computer. Each triangle tile corresponds to a different application, like an email program, or a personal calendar. Efforts to add computation to construction toys have met with The user activates the program through the tile face. The varying degrees of success. Fischer Technik, for example, was pieces have integrated mechanical and electronic among the first to enhance a mechanical construction kit toy magnetic connectors that allow the user to build a variety with limited computational abilities. Currently among the best of geometric forms that correspond to his suite of known is Lego Mindstorms, which provides a microcontroller applications. that end users can program to control motors, lights, and sensors. Lego Mindstorms provides only one microcontroller, Anderson et al.’s Computational Building Blocks (2000) (additional units cost $XXX), and this suggests a certain class of facilitates computer modeling with LEGO™ like blocks. constructions in which a single central “brain” controls a model. Computational Building Blocks are static pieces. As microcontrollers, sensors, and wireless communicationAlthough the Triangles have hinges, they assemble to continue to become cheaper and smaller we expect to seemake a static, rigid form. a new space of computationally enhanced construction toys, that comprise not only a single microprocessor perSeveral projects track movements of physical objects to kit, but in which each component may employ sensors,generate animation. Monkey™ is a specialized input actuators, and microprocessors, and communications. Asdevice for virtual body animation (Esposito et al. 1995). It part of a larger project to explore this design space ofresembles a mechanical mannequin with articulated computationally enhanced construction kits, we have builtlimbs. Instead of constructing a simulation of human a working prototype of one category of traditionalanimation and locomotion using a screen interface, the construction toy, a hub-and-strut geometry constructionanimator poses and moves the Monkey™ to define the kit. character’s animation. Topobo, another project involving character animation (Raffle et al. 2003), is a construction A construction kit may have various applications, beyondkit of articulating vertebra-like pieces for building posable its primary use as a toy. An architect might use a set offorms with embedded kinetic memory. The embedded blocks, for example, to model a building. A mechanicalmemory records the angular movement at the joints. or civil engineer can use a Meccano set to model aUsers build a creature, move the model across a terrain, kinematic lnkage or a structural support system. Aand then watch the model replay its movement from its chemist or biologist might use a physical model to thinkembedded kinetic memory. about the three-dimensional structure of a molecule or protein. A physical model complements the computerLike Topobo’s mechanical widgets, Phidgets is a graphics models and performance simulations byconstruction kit of physical computing widgets: sensors, providing a kinesthetic sense of the structure and behaviormotors, radio frequency ID readers, and a software of the artifact that the designer is exploring. interface for user interaction (Greenberg and Fitchett 2001). For example, users can use a motion sensor at a RELATED WORK doorway to activate a light in the adjacent room to signal An early effort, Building Block System (Aish 1979) was asomeone entering. Phidgets do not require any knowledge block set for interactively representing the structure andof processors, communication protocols or programming. physical properties of the world. Frazer’s (1981) 3D inputTheir ease of use, modularity and ability to facilitate event-driven interaction make them a handy resource for LEAVE BLANK THE LAST 2.5cm building tangible user interfaces. OF THE LEFT COLUMN CUBIK is a tangible modeling interface to aid architects ON THE FIRST PAGE and designers in 3D modeling. It takes the form of a FOR US TO PUT IN mechanical cube (Lertsithichai and Seegmiller 2002). The THE COPYRIGHT NOTICE! designer manipulates dials on the cube’s face to expand or contract its dimension. CUBIK’s corresponding graphic potentiometer user interface (GUI) displays in real-time how the cube is expanding or contracting. The communication between4 geometry and topologypopsicle stick hinge with rotational the GUI and CUBIK is bi-directional. The designer can potentiometer manipulate the physical cube through the GUI, or change5 geometry and topology,plastic hinge with rotational potentiometers the cube’s shape in the GUI via the mechanical cube. manufacturability</p><p>SPECIFICATION Among the many diverse categories of construction kit, the “hub-and-strut” form is of particular interest. As itsThe first prototype we used to demonstrate the concept name implies, a hub-and-strut construction kit compriseswas a cube made of thin wooden (shishakabob) sticks and hubs and struts, which correspond to the vertices andsurgical tubing, with bend sensors inserted to sense when edges of a graph. The specific design of the componentsthe cube was deformed. We used a microcontroller (first varies tremendously, giving rise to a wide variety of hub-an MIT Cricket, subsequently a Handyboard) to measure and-srut construction kits. For example, in TinkerToy,variable resistance of the bend sensors, and drive the the hubs (wooden spools with radially drilled holes)display (in VRML) of a three-dimensional model of the specify connection angles, are connected with fixedcube. This prototype only sensed geometry, and it was not length rigid struts. In ZomeTools, the hubs also fix themodular: one could not disassemble and reconfigure the angles, but unlike TinkerToy the hub angles are notcomponents, in part because it was difficult to work with planar, but three-dimensional, and the struts of variousthe sticks and tubing without disturbing the bend sensor. lengths are keyed to specific sockets in the hub. In XXXAlso, the bend sensor is relatively expensive, tends to the hubs are flexible and the struts rigid allowing theperform differently over time (with fatigue), and each unit model to flex and deform. In YYYthe hubs are rigid butperforms differently, requiring careful calibration. the struts (made of plastic straws) are somewhat flexible. In a traditional “ball and spring’ molecular modeling kit, holes drilled in color coded wooden spheres at the figure: earliest surgical tube prototype & VRML model appropriate bond angles for different kinds of atoms are connected by springs. Our current working prototype uses a combination of high-intensity LEDs and photosensors to determine model We chose for our initial effort to build a hub-and-strut kit topology, rotational potentiometers to determine model with flexible hubs. The kit must be able to serve as an geometry; and a microprocessor with a radio transceiver input device that can: to send information collected at each hub to a central base 1) determine the model’s topology—the ways hubsstation that assembles the information received and passes connect to one another. it along to a desktop computer.</p><p>2) determine the model’s geometry—the ways the model is flexed. Mechanics</p><p>3) send model topology and geometry to a host computerWe have tried several variations of of the mechanical for further processing design of the hubs, following the initial stick and surgical tubing prototype. We tried casting bend sensors into a in addition, we also want the kit to: serve as an output silicone hub (reminiscent of the flexible plastic hubs of device that can: the XXX toy). We tried a rigid hub design that accepts 4) highlight parts of the model. struts into sockets in the faces of a cube; this violated our specification for flexible hubs. We settled on a mechanical hinge design somewhat like an umbrella. IMPLEMENTATION Each socket is mounted at the end of two popsicle-stick summary of previous prototypes shaped pieces of wood (1 cm x 10 cm) that are hinged along their long edges. Our prototypes have three of 0 geometry surgical tubing, bend sensor, these hinged pairs, which allows the hub to flex from flat wooden sticks (120° between edges) to closed (almost 0° between 1 topology wooden cubes with lights and photosensors edges). See Figure XXX. </p><p>2 geometry bend sensor embedded in silicone mold</p><p>3 geometry and topologypopsicle stick hinge with sliding Geometry</p><p>“Popsicle-stick” mechanical hinge design</p><p>Topology To determine the model topology, the base station signals each hub, one by one, to turn on its LEDs. The brght light at the end of each of the sockets is transmitted along the length of the acrylic rod, and can be sensed by photocells in the sockets of any connected hubs. The base station polls all the other hubs to determine which of them are connected to the currently lighted hub, and through which socket. When the base station has finished lighting and potentiometers measure angle: sliding polling hubs, it has built a table of connections that taken (left) and rotational (right) together represent the model’s topology. We could have used electrical connections rather than optical ones, but the sequence of flashing LEDs is visually attractive and also reveals the topology sensing algorithm. </p><p>Left: sliding potentiometer measures Optical sensing topology angle; right: rotational potentiometer makes and measures hinge.</p><p>Communication Our first prototype used an MIT Cricket (a Motorola 68HC11 microcontroller board with two analog ports and infrared communication) to read the resistance values of bend sensors, but because we needed more i/o ports we began using the MIT Handyboard instead. We wired each hub to a sequence of i/o ports on the Handyboard, and ran a program on the Handyboard to light and poll the hubs as described earlier; then we sent the topology and geometry data along a serial line to a desktop computer for further processing. This configuration allowed us to develop the clear acrylic struts connect three struts mechanical and electronic design of the hubs and test the sensing algorithms. The major drawback of this approach is that the hubs must all be wired to the Handyboard. </p><p>We have therefore replaced the wired Handyboard with a wireless variation of the communications design. Each hub now contains a Basic Stamp 2 microcontroller (a veryFrazer, J., Frazer, J., and Frazer, P., New popular hobbyist board) with a Surelink radio frequency developments in intelligent modelling. In transceiver. The transceivers communicate with a single Proc. of Computer Graphics 81, pages 139- base station that, like the Handybaord, polls the hubs and 154. Online Publications, 1981. collects the topology and geometry data and sends it along a wired serial connection to a desktop computer. Esposito, C., Paley, W. B., and Ong, J. Of mice and monkeys: A specialized input device for virtual body animation. In Proc. of Symposium on Interactive 3D Graphics, CAD pages 109-114, 213, Monterey, California, Apr. 1995.</p><p>FUTURE WORK Gorbet, M., and Orth M. Triangles: Design of a limited production Physical/Digital Construction Kit. In Proc. of the Symposium on Designing Interactive Systems 1997: 125-128. 1997.</p><p>Greenberg, S. and Fitchett, C. Phidegts: Easy development of physical interfaces through physical widgets. In Proc. of the ACM UIST 2001 Symposium on User Interface Software and Technology, November 11-14, Orlando, Florida. ACM Press. www.cpsc.ucalgary.ca/grouplab/papers/ http://Phidgets.com</p><p>Gross, M. FormWriter: A Little Programming Language for Generating Three- Dimensional Form Algorithmically. In Proc. of CAAD Futures 2001, Eindhoven, 8-11 July 2001, pp. 577-588.</p><p>Hoberman, C. Faltstrukturen für temporäre direct-to-plastic rapid prototyped hub Gebäude (Temporary Unfolding Structures). Detail, Dec. 1996, vol. 36 no. 8, pages 1184- 1185. </p><p>REFERENCES Lertsithichai, S. and Seegmiller, M. CUBIK: A bi-directional tangible modeling interface. In Aish, R., 3D Input for CAAD Systems. Proc. of the Conf. on Human Factors in Computer-Aided Design, 11(2):66-70, Mar. Computing Systems, CHI 2002, pp. 756- 1979. 757. 2002.</p><p>Anderson, D, Frankel, J., Marks, J., Agarwala, Martin, F. Robotic Explorations: A Hands-On A., Beardsley, P., Hodgins, J., Leigh, D., Introduction to Engineering. Upper Saddle Ryall, K., Sullivan, E., Ydidia, J, Tangible River, New Jersey : Prentice-Hall, Inc. 2001. Interaction + Graphical Interpretation: A New Approach to 3D Modeling. In Proc. of Raffle, H., Parkes, A. and Ishii, H. Topobo: A SIGGRAPH 2000: 393-402. 2000. constructive assembly system with kinetic memory. In Proc. of the ACM CHI 2004, Camarata, K., Gross, M., Do, E. Navigational April 24-29, Vienna, Austria, ACM Press. Blocks: navigating information space with http://tangible.media.mit.edu/. 2003 tangible media. In Proc. of ACM Conference on Intelligent User Interfaces Tinker Toys. (2003). http://www.yesterdayland.com/popopedia/sh ows/toys/ty1079.php Erector Sets http://www.ideafinder.com/history/invention Vollers, K., Twist&Build: creating non- s/erectorset.htm orthogonal architecture. Rotterdam, The Netherlands: 010 Publishers. 2001.</p><p>Wrensch, T. and Eisenberg, M. The programmable hinge: toward computationally enhanced crafts. In Proc. of UIST 1998, November, San Francisco, California, pages</p>