A biologically inspired graduate school project taken on by a University of Maryland student could become a money-making commercial venture for the doctoral aerospace engineering candidate later this year.
Evan Ulrich's thesis topic - controlling the flight of a maple seed, or samara - has led to an unusual but surprisingly viable unmanned air vehicle that he is not only using as a dissertation topic but as the launch platform for his new company, RoboSeed.
Since beginning the project in 2005, Ulrich has built more than 100 versions of the patented device, which he says is the world's smallest single-wing rotorcraft. Wing spans have ranged from that of a maple seed, about 3.5cm (1.4in), to 50cm. The most recent version, which Ulrich is marketing to military and government agencies, features carbonfibre construction and an 18cm wingspan.
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With a 480mAH lithium polymer (LiPo) battery, the $500 device weighs 72g (2.54oz) and can fly for 15min at an altitude of 150ft (45m) under the control of an operator with a two-channel radio control unit. Alternate designs have flown for as long as 30min at up to 1,310ft altitude, says Ulrich.
During the research phase of the project, Ulrich studied the effect that changes in wing geometry have on the different flight dynamics of a samara through drop testing in the laboratory. "We found that the seed will travel in one of two flightpaths - either straight down or a helical flight path, the difference between the two being the wing angle," says Ulrich.
It turns out that a high wing angle, with respect to the ground plane, causes the samara to spin in place straight down while a low angle causes it to spin in a circular path, the diameter of which depends on the wing angle. This led to a control scheme that uses an electric motor and propeller to provide the rotational energy that gravity offers in nature, and a wing pitch mechanism to control the radius of the circular path. After the motor is running, the operator controls the flightpath through the pitch control only, with higher wing angles resulting in a tighter circle. If power fails, the device autorotates to the ground, seed-like, and the tough construction prevents damage to any components.
Trade-offs between weight and payload will be key going forward. Ulrich says about 30% of the RoboSeed's weight, or about 20g, comes as a result of protective features of the design, which have made it a rugged test platform.
The first job of the new company, which Ulrich hopes to devote his full attention to once he receives his doctorate degree later this year, is to develop sensor packages and a closed loop autonomous control system for the RoboSeed.
Ulrich plans to install a video camera payload, that in combination with a miniature on-board magnetometer for attitude control and software for image processing in an Apple iPad or other PDA device held by the operator, will allow for low-cost surveillance in combat zones or border areas.
"At a height of 150ft, the RoboSeed would give an extended line of sight up to 10 miles [16km] in every direction," says Ulrich. Estimated cost for such a system would be about $50,000 per unit, which would include the 40g sensor package and extra battery.
"With this particular application, we're able to compete with the Predator for border patrol," says Ulrich. "For $5 million, you could have 100 of these covering a 20-mile diameter circle each along the entire border." Given the simplicity of the device and its manual control, Ulrich says no US Federal Aviation Administration approval would be required.
Another potential military application will be to use the device for 3D mapping of tight areas, such as caves. For this work, Ulrich says the RoboSeed would have to be fully autonomous and carry a laser range finder for obstacle detection and avoidance, magnetometers for control and accelerometers for directional sensing.
Ulrich is hoping to work with Lockheed Martin on such a programme, with Lockheed supplying the sensor suite. Lockheed is also researching the maple seed concept internally with its Samurai nano air vehicle programme.
On the civilian side, Ulrich is trying to get the National Atmospheric and Oceanic Administration to consider the RoboSeed as a low-cost method of obtaining pressure, temperature and other data inside of tornadoes and hurricanes.
A video of Ulrich discussing and flying the RoboSeed at the University of Maryland on 10 September is below.
Source: Flight International
