Video: Helicopter senses surroundings

The helicopter in this video may weigh only 30 grams, but it carries a compass and motion sensors, can change course and warn fellow craft of obstacles it bumps into, and could even carry a small camera. It can also resist what might be called a King Kong attack – if swatted out of the air the tiny craft soon recovers and takes off again.

It was developed by researchers at Carnegie Mellon Silicon Valley in Moffett Field, California. It would make a great toy, but the team’s intentions are deadly serious. They aim to fly squadrons of “Sensorfly” craft that coordinate with each other to explore indoor environments – for instance, to check out buildings after a natural disaster.

The robots are built by adding custom processors, sensors and software to rotors and motors from an off-the-shelf toy helicopter. Each prototype costs only about $200 to build, says Pei Zhang, an electrical engineer working on the project with graduate student Aveek Purohit.

Bumping along

Indoor flight requires a craft to be small, light and able to negotiate walls and other obstacles. “Reality bites you a lot more indoors,” says Zhang. But Sensorfly is too small to carry the technology it would need to look for and plan around obstacles. Instead it uses simpler strategies to survive.


Each robot carries a radio, accelerometer, compass and gyroscope. Thanks to the accelerometers it notices if it bumps into something, then backs off and warns fellow copters nearby of the obstacle’s approximate location. Any time two or more of the helicopters are within radio range, they form an improvised data network to share information. Their design is “passively stable”: as long as the twin rotors are spinning, the craft will hover in place. Its shape is such that if it is knocked to the ground, the craft need only keep trying and it should be able to get airborne again.

Squadrons of the craft connect with each other using radio. They pass information between themselves and back to a controller, and use the time delay on the radio signals to track their relative positions.

Team work

The current prototypes can carry only 5 grams of cargo, but that is enough for a small camera or microphone, says Zhang. The networked helicopters are the most lightweight mobile sensor network to date, he says.

However, Kamran Mohseni, who with colleagues at the University of Colorado in Boulder developed a pack of small planes able to collect and share data, points out that the Carnegie Mellon group need to work on their flight times to prove the benefits of their approach. At present they can only sustain flight for 5 minutes. Zhang says he expects better batteries to extend that.

Sensorfly was presented at the Conference on Embedded Networked Sensor Systems in Berkeley, California, earlier this month.