Fly Spies

For the last five years, the DelFly team at the Delft University of Technology in the Netherlands has been designing miniature insect-like robots that fly around and stream live video back to their base controller. The team’s aim is to maximise aerodynamic efficiency and miniaturise onboard instruments.

It got a chance to put one of its creations into action two years ago, when a fire ravaged the university’s architecture building. The 14-storey building was beyond repair, but held valuable book and furniture collections. Video footage of the interior could help determine whether it was worth the risk of salvaging them. A week after the fire, team leader Bart Remes sent Del- Fly II, a 17-gram craft with a 28-centimetre wingspan, flapping up along the side of the building. At each floor, he paused it to peer in at the devastation through broken windows. When the DelFly was at the eighth floor, a crow dove from the roof and attacked it, slashing the thin Mylar film of its wings and sending it tumbling down to the ground. At first, Remes was shocked by the attack, but then he realised that the crow had given the Del- Fly the ultimate seal of approval. “It was quite impressive to see that nature itself thought we were part of nature,” he says.

The DelFly team is just one of a number around the world working to develop ever-smaller flying robots or unmanned aerial vehicles (UAVs). Some mimic insects. Others are miniaturised planes or helicopters. Still others take inspiration from seeds. Ultimately, these miniature flyers could investigate areas too dangerous for humans – burned-out buildings, collapsed mines, chemical spills – and beam back valuable information.

But first, there are major design challenges to surmount. The DelFly team has made only partial progress towards its goal of a fully autonomous flyer that can survey the interior of an unknown building on its own. Using two miniature cameras – one directed forwards and the other pointed downwards – the DelFly II can avoid some obstacles by recognising how far away they are and by following patterns on the ground, but it still requires significant human guidance via remote control.

The cameras also help the craft to steady itself on turns without the use of an on-board gyroscope. The base controller performs all image processing, further minimising on-board burdens. “We try to avoid adding extra components, which add more weight, consume more power and make the system more complex,” says Rick Ruijsink, one of DelFly’s developers.

The Smaller, The Better
Smaller than DelFly II is DelFly Micro, weighing just over 3 grams – including a camera – and with a wingspan of just 10 centimetres. As crafts get smaller, maximising efficiency becomes more critical and construction more difficult. Modelling of airflow around the wings also remains a challenge. The unusual “clap and fling” motion of the DelFlies, where a pair of wings on each side of the body meet each other and then flap apart, is especially difficult to model. So far, the Micro can fly forwards, but unlike the DelFly II it has yet to master hovering and flying backwards. “We hope to be able to do that this year,” says Ruijsink.

Predators that view the DelFly as an intruder may be less provoked by Roboseed, a small flying robot developed at the University of Maryland in the United States. It is modelled after the maple seed, which is attached to a single wing and is generally allowed to twirl through the air uneaten by birds. University researchers looked to nature for inspiration after attempting to produce a small UAV modelled on a helicopter and finding that the design was too complex and inefficient to be feasible.

“One of the unique things about maple seeds is that they fly with essentially no moving parts,” says Evan R. Ulrich, co-inventor of Roboseed and a graduate student of aerospace engineering. “All the other flyers in nature have very, very complicated and not yet fully understood mechanisms at work.”