Somos Stereolithography Resins Enables Fluid Motion for Robotic Spiders

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 Lifelike 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 this March in Lifelike 06 in Sunderland England.

Robotic Spiders with DSM Somos Stereolithography Resins

Key to this success was help from the product development specialists, Laser Reproductions and the innovative use of DSM Somos 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. in California.

A Joint Effort
The Autotelematic Spider Bots evolved from the leg joints up. The critical piece of the design was to construct an efficient robotic joint that allowed a highly fluid motion while reducing the number of motors necessary to achieve the fluidity. One common method for effecting motion of hexapod robotic legs is to use a series of servo motors at each joint, sometimes as many as two motors per joint, so for one leg with multiple degrees of motion you might have four motors per leg. This gets heavy and expensive when talking about robots with 6 legs as you could easily have 24 motors per robot.

Instead, Rinaldo’s unique design uses motors and pull string mechanics in combination with an intelligent servo-control system to actuate the legs. Each leg of this six-legged creature uses 2 motors per leg and this allows for a surprisingly fluid freedom of movement. The leg joint creation went through many design iterations with CAD imaging modifications and rapid prototyping from DSM Somos stereoltihography resins until the final design could be confirmed.

Rinaldo says, “When I saw the first robotic joint and leg working as I had designed, I was ecstatic. With 3D modeling and rapid prototyping I felt I had finally found an artistic/engineering medium, where pure idea of thought and imagination could be quickly brought into the physical world.”

The legs are based on a tension-compression structure and pull string mechanics. Each set of two legs created out of stereolithography using DSM Somos 9120 acts like a kind of flexible arch, which is held into compression by additional parts made from DSM Somos 8110 stereolithography materials and monofilament or 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 is 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, reaffirming this decision.”

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. The tripodic gait is the way cockroaches and other 6-legged insects walk, rather than the eight legs that define a real spider.

Final Creation
Once the leg design was finalized, the remaining body quickly followed. The manufacturing of the Spider Bots was done with rapid prototyping plastics, which allowed quick testing of the stiffness, flexibility and translucency of the plastics. The colored bodies are fabricated from an original rapid prototype model made out of DSM Somos 11120, a tough, rigid material which is ideal for producing molds because of it’s dimensional stability. Casts were done out of semi clear polyurethane plastic, impregnated with Pantone colors to give each robot an individual quality. 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 sight and LEDs for visual feedback. A miniature video camera mounted on one Spider Bot sends what the Spider Bot is seeing and these images are projected to a large screen and give humans in the exhibit the point of view of the Spider Bots.

In order to meet the festival’s deadline, the creation of the robot series from the revised and evolved 3D designs – to finished robot occurred in less than five months. “This is an incredibly fast evolution, where Laser Reproductions played a critical role in helping me finish the project,” states Rinaldo. “With their assistance and recommendations, I was able to complete the project on time.”

The Exhibit
The exhibit, Autotelematic Spider Bots 2006, at the AV Festival in March included 10 of the Spider Bots. They are 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. Rinaldo describes the display as, “an artificial life chimera; a robotic spider, eating and finding its food like an ant, seeing like a bat with the voice of an electronic twittering bird.”

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. When asked about other possible future projects, he explains, “I’d like to significantly reduce the total number of motors that are currently used to manipulate the robot from 14 to 3. I’ve been working on some ideas that would lend to a solution.”

In the meantime, the Spider Bots next premiere will be at the Hopkins Gallery at Ohio State University, beginning October 17th, for three weeks. After this 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.

Special acknowledgements
Professor Ken Rinaldo would like to thank the following for their contributions to the success of the Spider Bot project:

  • Matt Howard and Ross Baldwin, for their collaboration during the realization process
  • Laser Reproductions for their overall assistance and recommendations
  • Parallax Inc. for their powerful and easy to use microprocessors and sensors
  • AV Festival England and Honor Hager Curator for the exhibition invitation

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