Researchers make a robotic fish with a battery for blood

Enlarge (credit: James Pikul)
Lots of experimental robots involve a little bit of cheating. Rather than containing all the necessary electronics and energy sources, they have tethers and wires that provide power and control without weighing the robot down or taking up too much internal space. This is especially true for soft-bodied robots, which typically pump air or fluids to drive their motion. Having to incorporate a power source, pumps, and a reservoir of gas or liquid would significantly increase the weight and complexity of the robot.
A team from Cornell University has now demonstrated a clever twist that cuts down on the weight and density of all of this by figuring out how to get one of the materials to perform two functions. Like other soft robot designs, it pumps a fluid to cause its structure to expand and contract, powering movements. But in this case, the fluid is also the key component of a flow battery that powers the pumps. This allows them to put all the critical components on board their creation.
Going with the flow
So what's a flow battery? Batteries operate by having different reactions that take place at their two electrodes. For something like a lithium-ion battery, the intermediaries of these reactions—electrons and ions—immediately flow from one electrode to another, and the key chemicals spend almost all their time at the electrodes. In flow batteries, the chemical reactions still take place at the electrodes, but the chemicals reside in solution, rather than being confined to electrodes.
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