Robots are getting so light that they can be made to stand on the surface of water without breaking the surface tension. There is a big difference between something that floats in the water and something that just stands on top of it without getting wet. Most of the creators reference water skaters as their inspiration, but I have yet to see a skater bot kick for propulsion. There are some claims, but I say video or it didn’t happen. All of these seem to use vibration to chatter along on the surface. Here are some pretty good photos, and passable videos.
There are a few bots with accompanying info and some video here.
A very different and easy to make at home design here, with video.
I’m tempted to build one of these. It shouldn’t take much more than some thin wire, a cellphone vibrator, and a button cell to make a basic version.
Update: Here is another one that uses an electrical charge to destabilize the surface tension and cause propulsion. I’ve been thinking about this for a long time, and I’m glad someone got around to building it. I’m a little surprised the top speed is as low as it is. If you want to easily test the concept, put a little soap on one edge of something that will sit on the surface of water, like a little scrap of paper. It will move rapidly in the direction opposite the soap as the surface tension is destroyed. This robot has the benefit of not permanently reducing tension or befouling the water. (via bb gadgets)