Tuesday, March 10, 2009

Analysis: Caterpillars and Snakes

The Cologne deployment highlights the need for true robot snakes that can work in wet environments and interior of mixed rubble. The ASC is actually a caterpillar. The important point is just like real caterpillars and snakes, the mechanical versions have different ecological niches- I want both. We’re missing a snake from our arsenal of ground robots. Never forget that the US&R ecological niche requires a self-cleaning camera (the equivalent eyelids and tears) to permit rescuers to see as dust, dirt, and water collect on the lens.

The dear ASC (which we’ve nicknamed “Catey”) provides the smallest size on a fieldable robot I’ve ever seen, on par with those big fat hairy caterpillars that either delighted or grossed you out as a child. Like a real caterpillar, it is slow and has to “go with the flow” as it can bend but can’t necessarily climb. Unlike a caterpillar, it is pretty stiff, as only the “head” can bend- the forward motion comes not from undulation but from vibration, which is extraordinarily brilliant but provides less propulsion. Think of the current ASC as a partially paralyzed caterpillar that can’t blink, as if it evolved in the desert- which is great for a fairly dry pancake collapse- like when we used it so successfully at the Berkman Plaza II collapse. I’d like to see the ASC adapt to become a rainforest caterpillar, able to blink and work in mud (the latter may be impossible due to clogging of the cilia). But don’t get me wrong, I’ll take the ASC caterpillar just the way she is!

Snakes, on the other are usually bigger than caterpillars, but more powerful and have eyes that blink. A lot of rattlers have simple thermal sensors for better targeting that poisonous bite (which could be transferred to finding survivors). A robot snake that slithered (technically traverse motion) could climb and more aggressively attempt to penetrate irregular rubble. Notice that snakes are smooth. Many mechanical snakes (see http://www.engin.umich.edu/research/mrl/00MoRob_6.html) are tracked- lumpy and exposed. And big, just under the size of the Inuktun Extremes. Exposed segmented mechanical snakes (where the snake is a series of miniature tracks or wheels on articulated joints) collect mud and debris interfering with movement. And if there is a way for a device to jam or get tangled, it will. That’s why I am very excited about Howie Choset’s smooth, highly articulated snake (see http://www.cs.cmu.edu/~biorobotics/serpentine/serpentine.html ). He has been part of the CRASAR team since 2003 and it has been interesting watching his ideas about snakes for US&R evolve with each field exercise he and has students participate in. Anyway, what I want is the mechanical equivalent of a Texas brown snake, a snake that likes to burrow in moist compost (or a mixed rubble collapse).

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