Tiny Robot Walks On Water
| Published 9/24/04

Graphic by: Jenny Conner

About a year ago, scientists didn't even know how live water skimmers pulled off the feat of skimming on water. Now, they're making their own. A research team led by Carnegie Mellon engineering assistant professor Metin Sitti has built a small robot that can walk on water.

The prototype robot weighs about as much as a paperclip, and cost about $10 in materials to make. Nearly the same size as its non-mechanical counterparts, the prototype is a little more than a half-inch long. Its lightweight body is made from carbon fibers and eight two-inch steel wire legs, technically making it a water spider.

Despite being extremely fast for its size, the prototype has no brain, sensors or battery. It can move across the water at up to a meter per second. Considering size, that's about the same as you getting up from your chair and running 400 miles per hour to class. Instead of a complicated controller and brain system that would add weight, its "muscles" are controlled by just three circuits connected to a power supply.

Since it can be used on any still water, the possibilities for this simple prototype are almost endless. By attaching a chemical sensor, it could be used to monitor water supplies for contamination. With a camera, it could be used to explore or as a spy. With a net, it could skim contaminants or particles off the top of water.

Up until last year, researchers didn't even know how living water skimmers walked on water. It was thought that the insects used their legs to create waves to push themselves forward. However this idea was put to rest after a Stanford marine biologist pointed out that if water skimmers did this, hatchlings would then be unable to move because of not being strong enough. Newly-hatched water skimmers, however, move just as well as fully grown ones.

The simple answer is that water skimmers are light enough as to not break the surface tension of water. Therefore, the force they exert on the water creates a trampoline effect as the water pushes back on them and propels them forward.