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For the past three years, Ken Rinaldo, Associate Professor of Art in The Ohio State University's Art and Technology program has been working on a design to create a new method of robotic movement. With a commission from the AV Festival 06 England (an electronics arts festival in the United Kingdom) and collaboration with Matt Howard and Ross Baldwin (two former students of Rinaldo) the series premiered last March in Sunderland England.
Key to this success was help from the product development specialists, Laser Reproductions and the innovative use of stereolithography plastics. The ability to choose a particular plastic with specific degrees of flexibility allowed the idea to succeed. Also key were microprocessors and sensors from Parallax Inc.
The critical piece of the design was to construct an efficient robotic leg joint capable of smooth motion with a minimum number of motors. Rinaldo's unique design uses motors and pull string mechanisms in combination with an intelligent servo-control system to actuate the legs. Each leg of this six-legged creature uses just two motors while allowing surprisingly fluid movement. The leg joint went through many iterations using CAD and rapid prototyping until the final design was determined.
Stereolithography using flexible Somos 9120 was used to make each set of two legs which act like a kind of flexible arch. The sets of legs are held in compression by additional parts made from DSM Somos 8110 photopolymer and monofilament fishing line attached to the servo motors. The use of DSM Somos 9120, which mimics polypropylene, and Somos 8110, which mimics polyethylene, was chosen over recasting the parts in alternative materials as explained by Dave Evans, Model Development Lab Coordinator at Laser Reproductions, "Initially we thought about creating molds to produce the leg joints. We were going to use a urethane material but after careful consideration we realized that it would be very difficult to build molds for the leg joints so the stereolithography process was the best solution. To date, there have been no problems…"
The appearance of the leg design lent itself to the final decision to create a daddy long legs-like spider sculpture, where six legs allow the use of a tripodic gait (three legs on the ground at all times) to allow the robots to walk forward in multiple speeds and to turn in either direction. This is the way 6-legged insects walk, rather than with the eight legs that define a real spider.
Once the leg design was finalized, the remaining body quickly followed. The manufacturing of the Spider Bots was done with rapid prototyping parts, which allowed quick evaluation of the stiffness, flexibility and translucency of the materials. The colored bodies are molded from an RP pattern made out of DSM Somos 11120, a tough, rigid material which the company says is ideal for producing molds because of it's dimensional stability. Part were cast using semi-clear polyurethane plastic, impregnated with colors to give each robot an individual identity. The final size of each of the Spider Bots was approximately 2 feet by 1.5 feet.
The bodies were then outfitted with a variety microprocessors and sensors from Parallax Inc. in order to make the spiders robots come to life. Some of the advanced features are: a left and right hemisphere microprocessor approach to parallel processing, blue tooth technology for intercommunication between the robots, infrared eyes for sight, ultrasonic ears for sound and LEDs for visual feedback. A miniature video camera mounted on one Spider Bot shows interacting visitors what that robot is seeing by means of a large screen projection TV display.
In order to meet the festival's deadline, the robots had to be finished in less than five months. The exhibit, Autotelematic Spider Bots 2006, at the AV Festival in March included 10 of the Spider Bots. They were designed to interact with the public in real-time and self-modify their behaviors, based on their interaction with the viewer, themselves, their environment and their food source. Since the show, Rinaldo has received numerous requests for a commercial kit to create Spider Bots, which he will be working on in the coming year.
In the meantime, the Spider Bots will appear at the Hopkins Gallery at Ohio State University, beginning October 17th, for three weeks. After that they will travel to the Aboa Vetus & Ars Nova Museum Turku, Finland in April 2007 for the Digitally Yours exhibition and then to the Kerava Art Museum in Kerava Finland.
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Special acknowledgements:
Professor Ken Rinaldo would like to thank the following for their contributions to the success of the Spider Bot project:
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