Tiny robot insects might seem little more than fun, geeky gadgets to some, but the potential for these cyber-critters in areas like search and rescue, agriculture and hazard detection is massive – and so are the hurdles. Power-supplies, onboard-sensors, control and stability are all problematic at the micro-scale. It's this last issue – stability – that researchers at the University of Southern California (USC) have been working on with their Bee+, drawing inspiration – yet again – from the insect world.

Micro-scale, insect-like flying-robots have been flying around for a while now. There was the DARPA-funded robot fly in 2007 (which just went up and down), for example, and the three-gram (0.1-oz) DelFly Micro in 2008, declared the following year by Guinness Book of Records as the "smallest camera-equipped aircraft in the world." But when Harvard's 80-milligram (0.0028-oz) RoboBee first flew in 2013, it made the DelFly Micro look like an albatross with a brick in its pocket.

It's the RoboBee format which the USC research team has expanded upon in its Bee+ project, which was submitted to IEEE Robotics and Automation Letters this month. Harvard's RoboBee was limited in its maneuverability by the fact that it had only one pair of wings . This made flight-control difficult and flight-stability somewhat wiggly. With one pair of wings – each controlled by a tiny 25-mg, piezoelectric actuator – the operators of the RoboBee could influence roll, pitch and thrust, but not yaw.

The USC team observed that to be able to add yaw control to the mix, the Bee+ really needed four wings, as real insects do, but this risked adding significant weight to the robot. The actuators on the RoboBee already made up 50 mg of its 80-mg total, and adding two more would make the tiny robot too heavy to fly.

So, the USC team made lighter, better actuators. The RoboBee uses bimorph actuators, made up of three layers. The two outer piezoelectric layers contract alternately via a signal, and this in turn bends the inner layer back and forth, thus flapping it like an insect wing. In contrast, the USC team created unimorph actuators. These employ just one strip of piezoelectric material which move the passive layer back and forth. The resulting flight control improvements means that the Bee+ is able to following a path and avoid obstacles. And because these unimorph actuators are simpler, they're also cheaper to build.

In fact, the unimorph actuators are half the weight of bimorph versions which means that even with four 33-mm (1.3-in)-long wings, the Bee+ weighs in at only 95 mg (0.0033 oz). And since the load of the entire robot is distributed across four wings instead of two, the durability and life expectancy of a Bee+ is expected to be much greater than that of its two-winged cousins.

The path ahead for flying micro-robots is still a difficult one however. The Bee+ still weighs around 10 times that of a bumblebee and issues of onboard power and microcircuits small enough to make viable payloads still need to be addressed, with skillsets required from many disparate scientific disciplines. So don't go ordering your robo-beehive just yet.

A paper detailing the development can be accessed online.

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