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Midterm Proposal: Turtle Robot

February 28, 2010

Initially, my plan was to build a simple drawing machine along the lines of the turtle robots of Seymour Papert and W. Grey Walter, with, effectively, two large wheels in the back that could be turned in either direction, and a smaller gimbal in the front.  Utilizing it to execute programmed patterns of greater and greater complexity, this would essentially be a hands-on study of Papert’s ideas of “body syntonic” reasoning, and the utility of simple physical computers for teaching relationships between the physical world and programming.  The introduction of additional turtles could be used to study flocking patterns, and other types of group behavior.

This being a mechanisms class, however, I recognize that this idea is more focused on programming, so I took a step back and looked at the turtle itself.  The historic turtle robot mechanism is well understood at this point, and the parts for assembling it are readily available.  I personally have not built one, but began to feel that perhaps it would be more interesting to actually look at the motion itself, and to begin to think about the possibilities for the various types of motion.  W. Grey Walter’s BEAM principles give an excellent framework with which to begin: a turtle is either a crawler or walker.  Thinking in this way, it is obvious with regard to drawing machines that the type of drawn pattern can be a fuller expression of the type of mechanical motion.

Looking at the way a turtle actually moves, it is a good deal more complicated than two wheels and a gimbal:

[Eastern Box Turtle Walking]

Working with more lifelike motion as well would introduce a certain impression of randomness — “pseudo-random” — to the machine’s behavior, as the motion might be the result of multiple overlaid systems.  There is of course the danger of entering the “uncanny valley” where it is eerily real, but where something is wrong, a little off; I’m not too worried about that at this juncture.  If I can even achieve the jerky wonder of a Victorian metal toy or an old arcade game, I would count that a modest success.

The front and rear legs of the turtle are anatomically completely different, the front actually being more similar to our arms:

The shoulder blades are actually within the rib cage, however, rather than outside it.  There’s a very interesting piece on this, and how it likely led to the development of the shell here.

My proposal for the Mechanisms Midterm is to model this method of motion as closely as possible with a LEGO prototype, utilizing other materials such as wire as necessary.  I recognize that the rotational geometry of the joints is quite complex, so my initial prototypes will try to break that motion down into planar vectors.

As for power, at this point I’ll probably just stick with electric LEGO motors, but I am interested in trying some other power sources.  Instead of thinking of them simply as different power sources, but rather different motive forces, hydraulics and steam for example can be harnessed for different physical expression.

Shahar Zaks and I will be collaborating on this.


From → Mechanisms

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