Motion System Design

Creepy crawlies go robotic

For the past three years, Ken Rinaldo, associate art professor at The Ohio State University's art and technology program, has been working on a design to create a new method of robotic movement. Rinaldo originally received a commission from the UK's largest digital arts festival — the Lifelike AV Festival 06 — to develop robotic spiders. The project involved help from product development specialists at Laser Reproductions, Gahanna, Ohio, and the use of stereolithography plastics from DSM Somos, Elgin, Ill. Rinaldo also used microprocessors and sensors from Parallax Inc., Rocklin, Calif.

The “spider bots” evolved from the leg joints up. The critical design challenge was to build an efficient robotic joint that allows fluid motion, and to reduce the number of motors necessary to achieve it. In previous robotic leg design, a series of servomotors actuated each joint, but this can get heavy and expensive for robots with six legs.

Instead, Rinaldo's design uses motors and pull string mechanics in combination with an intelligent servocontrol system, using just two motors per leg. Joint creation went through many design iterations with CAD imaging modifications and rapid prototyping from DSM Somos resins until the final design was confirmed. Each set of two legs created out of stereolithography materials acts like a flexible arch, held into compression by additional parts plus monofilament or fishing line attached to the servomotors.

Once leg design was finalized, the remaining body followed. Spider bots were made using rapid prototyping plastics, which allowed quick testing of stiffness, flexibility, and translucency. Each robot is approximately 2 × 1.5 ft.

Bodies were outfitted with microprocessors and sensors from Parallax. Advanced features include a left and right hemisphere microprocessor approach to parallel processing, blue tooth technology for intercommunication between robots, infrared eyes, ultrasonic ears, and LEDs for visual feedback.

Since the spiders' debut at the Autotelematic Spider Bots March 2006 show, Rinaldo has received requests for a commercial kit to create the robots. He's also busy working on reducing the number of motors used to manipulate the robot from 14 to three.

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