Water striders glide on the surface of the water, supported by the surface's tension, and scientists have now created a microrobot version of the insect that uses special leg structures to move across the water. The WaterStrider robot was built by a team led by Washington State University associate professor Nestor-O. Pérez-Aranchibia and engineering doctoral student Connor Trigstad. The researchers also built a smaller, simpler water bug-inspired robot called MiniBug.
Of course, the WaterStrider robot is the most compact of the two, measuring just 22mm in length (the MiniBug is 8.5mm) and weighing just 56mg. Its body is mostly made of carbon fiber, using four disc-shaped feet to maintain surface tension so it doesn't sink.
The really interesting part of the robot, though, are the "shape memory actuators" that move its two arms/fins. At just 7mm long, it is reportedly the smallest device of its kind to date.
The actuator consists of two thin wires made of nickel-titanium alloy that shrink when heated and relax again when cooled, returning to a longer default state. When exposed to electrical current, the wire heats up, causing it to shrink. When the current stops, the wire cools and returns to its "memory" longer state.
So by applying a pulsating current, you can make the wire rapidly switch back and forth between the two states, flapping the connected arm in the process. In this way, WaterStrider is able to flap its arms 40 times per second and "row" on the water at a speed of about 6 millimeters per second. With a different configuration, the pushrod can lift up to 155 times its own weight.
Perez-Arancibia, Trigstad and their colleagues are currently working to integrate power supplies into the robots, and they also hope to develop other insect-inspired robots that can move both above and below water.
These robots could one day have applications in areas such as artificial pollination, search and rescue, and environmental monitoring, while the actuators themselves could also be used for tasks such as microfabrication and robot-assisted surgery.
A paper on this research was recently published in the IEEE: Robotics and Automation Society International Conference on Intelligent Robots and Systems.
This isn't the first water robot we've seen, though. Previous examples have moved by manipulating surface tension and heat-sensitive films.