Future drones equipped with the foldable wings would be able to squeeze through narrow spaces, manoeuvre through complex environments and avoid each other in air just as the flying creatures can.

Presenting their research in IOP Publishing's journal Bioinspiration and Biomimetics, the team led by Stanford University’s Amanda Stowers described one of the first mechanisms allowing the wing to morph completely passively, without the need for actuation.

Made of carbon fibre and Mylar film, each of the two bird-like arm wings of the drone was connected through a separate 3D printed joint initiating the flapping. Additional hand wings were attached through what the researchers called wrist joints, which was hinged to allow the hand to fold and unfold while the arm was flapping.

The researchers performed theoretical, numerical and physical simulations on the robotic wing and successfully demonstrated that when the wing flapped, the folded hand wing was able to unfold back to the full wingspan configuration passively.

“'Both the math and simulations worked out, showing that both tiny and big flapping wings can all morph passively within a wing beat,” said the study’s co-author David Lentink.

The hinged wrist joint also allowed the robotic wing to temporarily morph its hand when it came into hard contact with a rigid object; in this study the researchers used a 7mm steel rod. The joint allowed the robotic wing to comply with the object at impact and, after impact, the flapping motion caused the wing to automatically re-extend.

This is similar to how the flexible feathers of a bird allow for impact with obstacles without affecting the structural integrity of the wing.

“While birds are capable of responding to unexpected disturbances to their wings, these same disturbances would break the wings of most drones,” said the lead author Amanda Stowers. “By adding a passive wrist joint, the flapping wing we have produced can withstand an impact and recover automatically back to its original position.”

The researcher said the mechanism could lead to more robust future drone wing designs.

“I advised Amanda to hit her robot wing hard with a stick to see how well it could handle hard impact,” Lentink described. “We were both impressed that she could basically use a rod like a baseball bat and hit the hand wing of the robot, and it would still recover just fine.”

Read more: http://eandt.theiet.org/news/2015/mar/foldable-drone-wings.cfm

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