German scientists say that, in future, it will be possible to use miniature, fuel-cell-powered robot helicopters to search for people trapped in damaged buildings, check out traffic or investigate contaminated terrain.
The mini-copter will be powered by a very light fuel cell that weighs only 30g and has an output of 12 watts.
That’s roughly the same weight as the small die-cast models of Lightning McQueen or any of his chums from the animation, Cars, and the power rating of a car sidelight bulb.
The old saying that “there is strength in numbers” also applies to fuel cells. To deliver a high enough power output, a number of cells have to be connected in series.
Manufacturers normally stack the fuel cells – a structure consisting of several metal plates, each containing one channel for air and one for hydrogen. This makes the fuel-cell stack quite heavy.
Together with colleagues at the Technical University of Berlin, researchers from the Fraunhofer Institute for Reliability and Microintegration have cracked that challenge by producing a miniature stack with a power output more usually found in systems weighing several hundred kilograms.
They say the fuel cell is light enough to power a 20cm long helicopter that’s not much different to the radio-controlled mini-copters that can be so readily bought today. These rely on capacitors to provide power, which severely limits their time in the air, or tiny petrol-fuelled engines. How did the researchers manage to reduce the weight of the fuel cells so dramatically?
“We use very thin, planar fuel cells,” says IZM team leader Robert Hahn.
“We have replaced the metal plates with lightweight plastic spacers.”
The researchers have no need for an additional pump to provide an adequate air supply: the wind generated by the helicopter’s rotor blades goes directly into the air vents.
The scientists had to devise a solution for the hydrogen supply, too, as a conventional pressure tank would be too heavy for the helicopter.
“We have built a small reactor containing solid sodium borohydride. If we inject water, this produces hydrogen,” adds Hahn.
Since the helicopter always needs about the same amount of energy to stay in the air, the reactor always has to produce a consistent quantity of hydrogen.
The researchers have already built a prototype of the lightweight fuel cell. The helicopter is expected to take off, powered by this fuel cell, in just over a year’s time.
For the scientists, the next step is to adjust the hydrogen production to cater for fluctuating energy requirements. There are plenty of applications for such a fuel cell: it could be used as a charging point for laptop computers and cell phones – and that’s just the start.