Posey: Instrumenting a Poseable Hub and StrutConstruction ToyMichael Philetus WellerCoDe LabCarnegie Mellon UniversityPittsburgh, PA, [email protected] Yi-Luen DoACME LabGeorgia [email protected] D GrossCoDe LabCarnegie Mellon UniversityPittsburgh, PA, [email protected] describe Posey, a computationally-enhanced hub-and-strut con-struction kit for learning and play. Posey employs a ball and socketconnection that allows users to move the parts of an assembledmodel. Hubs and struts are optocoupled through the ball and socketjoints using infrared LEDs and photosensors. Wireless transmittersin the hubs send connection and geometry information to a hostcomputer. The host computer assembles a representation of thephysical model as the user creates and configures it. Applicationprograms can then use this representation to control computationalmodels in particular domains.KeywordsConstruction Kits; Tangible; Poseable; ToysCategories and Subject DescriptorsK.3.1 [Computers and Education]: Computer Uses in Education;H.1.2 [Models and Principles]: User/Machine Systems; H.5.2 [In-formation Interfaces and Presentation]: User Interfaces, Inputdevices and strategies1. INTRODUCTIONPosey is a computationally-enhanced poseable hub-and-strut con-struction kit. Its hub-and-strut form maps to model anything thatcan be described in a graph structure, for example an articulatedskeleton, a chemical molecule, a kinematic linkage or a buildingstructure. Figure 1 shows our friend Amanda using Posey to createand animate a bear character.Construction kits display a variety of qualities that have endearedthem to several generations of children and educators. Foremostamong these qualities is that children enjoy playing with them, andthrough play they are introduced to the rewards of working outtheir own plans and dreams in a tangible medium that demandsthe resolution of issues of form and structure. Working out de-sign problems with construction kits builds both general problem-solving skills and strengthens a child’s ability to think and imag-ine in three dimensions. Construction kits are also used to modelPermission to make digital or hard copies of all or part of this work forpersonal or classroom use is granted without fee provided that copies arenot made or distributed for profit or commercial advantage and that copiesbear this notice and the full citation on the first page. To copy otherwise, torepublish, to post on servers or to redistribute to lists, requires prior specificpermission and/or a fee.Copyright 200X ACM X-XXXXX-XX-X/XX/XX ...$5.00.Figure 1: Assembling a bear puppet with Posey and our PuppetShow application.the properties of particular domains. For example Lincoln Logshelp children understand and explore the design space of log build-ings; plastic molecule kits (Figure 2(b)) help students build a robustunderstanding of the geometry of molecules and the inter-atomicforces that govern their formation. And perhaps most importantlythe open-ended nature of construction kit play introduces childrento the hacker ethos of building things as a way of having ideas.A canonical instance of a poseable hub-and-strut kit is Tinkertoy,(Figure 2(a)) which consists of circular wooden hubs with holesdrilled in the center and around the circumference and woodenstruts of varying lengths. Many hub-and-strut construction kitssuch as Zome Tools have fixed connection angles between hubs andstruts. While a Tinkertoy hub fits tightly onto a strut inserted intoone of its perimeter sockets, a hub spins freely on a strut insertedinto its center socket, allowing the construction of kinematic mod-els. Tinkertoy demonstrates several of the qualities of the hub-and-strut construction kit form that we believe makes it a particularlyinteresting tangible interface:1. The rules for assembling pieces are straightforward and sim-ple to grasp: any strut connects to any hub in the same way.This accessibility promotes experimentation. In contrast, Lego’sconnection rules are more complex: bricks fit together in sev-eral different ways, and connecting two bricks creates subtleconstraints on future operations. Lego models are often real-ized by following step-by-step instructions.2. Hub and strut kits lend themselves to building kinetic poseablemodels. With Tinkertoy in particular, the combination of the1(a) a vehicle built with Tin-kertoy(b) model of Asparaginewith Molymod kit(c) lay figure for ex-ploring human poses(d) the ball and socket connec-tion of the ZOOB constructiontoy affords posingFigure 2: Some examples of uninstrumented hub-and-strut construction kits.ability to rotate certain connections and the scale of the strutsinvites animating models through physical manipulation.3. The graph structure of a hub-and-strut model can be mappedto a wide variety of domains.These properties of the hub-and-strut interface have already beenleveraged for several domain-specific tools. Chemistry modelingkits such as Molymod, shown in Figure 2(b), take advantage of thefirst property to allow students to quickly explore the space of pos-sible organic molecules. Although they are not exactly a construc-tion kit, so-called "lay figures" like the one shown in Figure 2(c)take advantage of the second property to allow the exploration ofposes of the human figure.Since Aish first proposed that physical blocks could be used asan interface for describing 3D models to a computer [1] researchershave constructed a variety of these sorts of kits. By enabling ap-plications running on a personal computer to monitor the topol-ogy and configuration of assemblies as they are manipulated thesecomputationally-enhanced construction kits promise to allow soft-ware developers to create novel and accessible environments forundirected play. These applications can improve on traditional con-struction kits in two ways: they can map additional domain-specificinformation to the current assembly, and they can provide feed-back in response to manipulations of the assembly. Systems suchas Computational Building Blocks [2], and others discussed be-low, add computational power to traditional physical constructionkits, lending themselves to creative exploratory and ’construction-ist’ play.Until now there have been no poseable kits instrumented to cap-ture both the topology and geometry of the model. Prominently, theTopobo project [16, 17] has demonstrated the potential of poseableconstruction kit interfaces, but most of the pieces are