Here is a spring-loaded quadcopter that changes shape to fly through narrow gaps. Its sprung hinges allow the arms to fold downward when low thrust forces are produced by the propellers, resulting in reduction of the drone’s size by 50%. This mechanism allows this drone to pass through narrow areas not possible for regular quadcopters.
When high thrust forces are produced by the propellers, the arms go back to their original position. The above video shows UC Berkeley’s morphing drone in action.