Tuesday, March 2, 2010

Moai Model

Just a quick followup to my post about 3D printed moai. I received the moai kindly printed by Mark A. Ganter. The actual item is about 8" tall and is a perfect replica of the computer model I created with Photosynth. The texture of it is a bit grainy which is a function of the powder used to generate the object. It is infused with wax to make it more robust. All in all feels like the volcanic tuff used to create the real moai. What is most important, however, is the fact that the details are correct, in particular, the center of mass. All other models made for transport 'experiments' have been based on some basic measurements and a bit of artistic interpolation. This model, on the other hand, is a reliable approximation of the real deal. Thus, when we evaluate ideas about moving the statues, we can get a real "feel" for how an actual moai might respond. Other than Pavel Pavel, the Czech engineer who moved an actual moai and Heyerdahl who dragged one across the beach at Anakena, no other experiment has made use of an accurate model. In general, then, other conclusions have been drawn simply on the basis of weight and size of a big statue-like object. Here, we can really see the limits of motion that reflect those likely present in real moai.

Playing with the model is fascinating. The center of gravity, as measured on the real moai, really is slightly forward which gives the statue a general forward lean. The front edge of the statue is rounded like the real ones and slightly flattened on the sides. Together this means that when you tip the statue slightly to the side (and a small bit forward) it "rocks" along the front edge and takes a step forward. Tipping to the other side reverses the motion and causes another "step." These things really can walk. And it takes just a small bit of energy to do so and is very stable - the shape of the front edge is such that the forward lean turns into a twist. It also means that there is no friction as the surface is not sliding on the ground -- rather the statue rocks along the edge. Absolutely amazing.


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