MIT's Computer Science and Artificial Intelligence Laboratory (MITCSAIL) created this graceful fishbot that can swim around a lot like a regular fish.
Via the creators:
Existing autonomous underwater vehicles (AUVs) have traditionally been tethered to boats or powered by bulky and expensive propellers.
In contrast, SoFi has a much simpler and more lightweight setup, with a single camera, a motor, and the same lithium polymer battery that's found in consumer smartphones. To make the robot swim, the motor pumps water into two balloon-like chambers in the fish's tail that operate like a set of pistons in an engine. As one chamber expands, it bends and flexes to one side; when the actuators push water to the other channel, that one bends and flexes in the other direction.
These alternating actions create a side-to-side motion that mimics the movement of a real fish. By changing its flow patterns, the hydraulic system enables different tail maneuvers that result in a range of swimming speeds, with an average speed of about half a body length per second.