This is a cheap and easy to build ROV (Remotely Operated Vehicle). I came up with it because I wanted to create a minimalist aquatic robot that avoided the traditional annoyance of needing to get / make waterproof motors for ROVs. This ROV uses a new form of aquatic propulsion that works via the creation of multiple standing vortices around the ROV's asymmetrical hull (if this isn't new please let me know). The propulsion system doesn't require contact of any actuator with the surrounding water, and is very easy to build and is very robust.
Previous bio-inspired ROVs have used flapping fish-like fins to move through the water. Although these fins work by creating vortices along their surfaces, the ROVVor creates constantly maintained, standing vortices around its hull. These standing vortices are maintained by a high frequency vibration of the vehicle, induced by an internal pager motor. The vortices seem propel the vehicle through the water due to the vehicle's asymmetrical hull shape which must create some imbalance in the vortice's forces applied to different sides of the vehicle.
Due to its ease of implementation and robustness, this propulsion mechanism could potentially be useful for creating nano-scale ROVs (would need some way to vibrate the 'actuator molecule'), although at the molecular scale vortices might not work in the same way. Due to the ROVVor vortex-drive's minimal actuator displacement (compared to spinning propellers of flapping fins) it could also be useful for military applications to avoid detection. On a lighter note, the cheapness and ease with which the ROVVor can be created, and the interesting-ness of the way in which it works would make it very conducive to introducing kids to robotics in general and specifically to ROVs.