New wing can help drones manage collisions

Researchers in the US have created a flapping robotic wing that can recover from mid-air collisions.
By examining the wings of birds and bats, the researchers at Stanford University, have created a mechanism that could allow drones to easily squeeze between obstacles, such as branches of a tree, and fully recover after accidental hard impacts.
When it comes to flying, birds such as pigeons and swallows can morph their wings until they are tucked close into their body, allowing them to pass through gaps.
In their study, the researchers created one of the first mechanisms in which the morphing of the wing was completely passive, requiring no actuation to fold or unfold, making the wing much lighter and more reliable.

The robotic wing was modelled on bat and bird wings and was made using carbon fibre and Mylar film. Similar to a bird wing, each of the two robotic wings had a wrist joint, which were custom built using a 3D printer.
The pin joint connected the arm wing and the hand wing. The arm wing attached to the body of the robot at the shoulder joint, which initiated the flapping. The complete wing set had a wingspan of 400 mm and a length (chord) of 80 mm.

The wrist joint of the wing was hinged so, as the rest of the wing flapped, the hand could freely fold and unfold over the arm, much like origami folding, without any actuation.

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.
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 lead author of the study 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," she said.
The study is published in Institute of Physics Publishing's journal Bioinspiration and Biomimetics.