Autonomous Robots 12, 211–222, 2002c 2002 Kluwer Academic Publishers. Manufactured in The Netherlands.Roball, the Rolling RobotFRANC¸ OIS MICHAUD AND SERGE CARONLABORIUS—Research Laboratory on Mobile Robotics and Intelligent Systems, Department of ElectricalEngineering and Computer Engineering, Universit´e de Sherbrooke, Sherbrooke, Qu´ebec, Canada J1K 2R1http://www.gel.usherb.ca/laboriusAbstract. Designing a mobile robotic toy is challenging work. The robot must be appealing to children and createinteresting interactions while facing the wide variety of situations that can be experienced while playing with a child,and all at a reasonable cost. In this paper we present Roball, a ball-shaped robot that moves by making its externalspherical shell rotate. Such design for a mobile robotic toy shows robustness in handling unstructured environmentsand unconstrained interactions with children. Results show that purposeful movements of the robot, its physicalstructure and locomotion dynamics generate interesting new games influenced by the environment and the child.Keywords: spherical robot, mobile robotic toy, educational and pedagogical robot, autonomous robot1. IntroductionThe 1980s were the years of the personal computer rev-olution, followed in the 1990s by the WWW/Internetrevolution with the growing interest in the concept ofinteraction, creating interesting and appealing ways ofexchanging information between computers and users.The primary focus for the next decade is interaction(not just for Internet but with electronic devices thatoperate in the physical world), using sensors as the keytechnology to create what can be called “smartifacts”.(Saffo, 1997)Interaction is surely one concept of great importancefor the toy industry, and commercial interest for interac-tive toys is expanding rapidly. Robotic pets like Furby,Poo-chi or the sophisticated robot-dog Aibo from Sonyand part of the MUTANT project (Fujita et al., 1998)are now entertaining children of all ages. Roboticdolls like My Real Baby from the association betweenHasbro and iRobot inc., or Miracle Moves from Mattel,are making their way into our homes. While it has beenthought that mobile robots would initially be commer-cialized to accomplish house chores like vacuumingand lawn mowing, technological development and re-search are still required to reach the level of precisionand effectiveness to make such task-oriented robots bewidely used, working as good or better than humans.Developing a robot that has to interact in interestingways with one or many users is a much more reason-able goal to achieve. A child will tolerate that his orher robotic toy sometimes stumbles or falls for somereasons, or that it does not react appropriately to someevents: this will just be part of the game, and the robot’sperformance will be evaluated based on its ability toentertain.However, this does not mean that designing robotictoys is not without its challenges. Children are ex-tremely hard on their toys: they grab them, throw them,kick them, put them in places they should not be in (dirt,water, modeling compound, ...), etc. Electronic prod-ucts are easily affected by these conditions. High techtoys would usually cost more because of the additionalprocessing, electrical and mechanical components re-quired to create interactions with the child, and par-ents will think twice before paying more for somethingthat might get damaged easily. The ability to create ap-pealing and meaningful interaction is also fundamen-tal. The physical appearance of toys is still essential,but now interaction is an additional concern and canbe done in various and novel ways: speech, sounds,facial expressions, visual cues and movement. Thesecharacteristics all contribute to the life-like quality ofrobotic toys. In that regard, the ability to navigate au-tonomously and purposefully is especially interesting212 Michaud and Caronsince the variety of situations that a mobile robot wouldencounter in a household or playroom environment(which will surely not be a uniform surface free of ob-stacles) also presents important challenges for robots.So the goal is to design a mobile robotic toy that canmanage unconstrained interplay situations experiencedwhile interacting with children in real life settings, andall at a reasonable cost. Children like to play with alot of things, and many different types of robotic toyscan be imagined. To design such robot, we followed aspiral model for engineering design (Pressman, 1992).The idea is to outline initial requirements, formulatesolutions, implement a prototype and evaluate it, andrepeat this cycle with increasing levels of complexityand completeness. This paper reports on the first cycleof this design process of a sort of mobile robotic toy.Mainly, it explores the use of a rolling robot namedRoball as a mobile robotic toy. Roball is a ball-shapedrobot that makes its external spherical shell rotate forlocomotion. We present the proof-of-concept prototypeand observations made of children interacting with therobot in unconstrained conditions, in order to evaluatethe potential of having such robot be used as a toy andhow its design can be refined and used for entertainmentor educational purposes, and to study human-robotinteractions.The paper is organized as follows. Section 2 firstoutlines design specifications that we consider impor-tant for designing our mobile robotic toy. Section 3describes the hardware and locomotion mechanism ofRoball. Comparison with other rolling robots is alsoprovided. Section 4 then addresses how we use Roballas a mobile robotic toy, with a description of thesoftware design. Observations made of children whoplayed with Roball are presented. Section 5 presents ananalysis of the observations made and outlines poten-tial directions to take in designing mobile robotic toys.2. Design ConsiderationsFour elements guided our design of Roball in this firstcycle of the design process:• Operation in Unconstrained Environments. Childrenlike to play with toys in all kinds of places, indoorand outdoor. In such context, a mobile robotic toymust be capable of working on different operatingsurfaces (wooden floor, ceramic, carpets, etc.), andit might encounter a great variety of objects (othertoys, shoes, clothes, etc.), obstacles (walls, couch, ta-ble, chairs, stairs, etc.) and entities (dog, cat, people,etc.). The locomotion mechanism and the physicalstructure of the robot have a direct influence on