The mechanism allows future flying robots 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 to their body, allowing them to pass through narrow gaps.
The Stanford 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.
"While birds are capable of responding to unexpected disturbances to their wings, these same disturbances would break the wings of most drones. By adding a passive wrist joint, the flapping wing we have produced can withstand an impact and recover automatically back to its original position," explained lead study author Amanda Stowers.
"Furthermore, the flapping wing can resist impact with minimal added weight and without any computer intelligence or power," Stowers noted in the journal Bioinspiration and Biomimetics.
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 researchers performed 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. This is similar to how the flexible feathers of a bird allow for impact with obstacles without affecting the structural integrity of the wing.
This finding will greatly help make flapping winged drones much more robust.
"This is essential if we ever want to safely fly through a forest or land in a tree like a bird," study co-author Dr David Lentink concluded.
