Here is a shape changing quadcopter that can reconfigure itself mid-flight. Just like a regular drone, it has 4 motors but changes shape with freely-rotating hinges. Nathan Bucki, Jerry Tang, and Mark W. Mueller are the researchers behind this projects. As they explain:
Morphing is achieved through freely-rotating hinges that allow the vehicle arms to fold downwards by either reducing or reversing thrust forces. Constraints placed on the control inputs of the vehicle prevent the arms from folding or unfolding unexpectedly.
[HT]