In the past few months, we have covered a bunch of interesting modular drones. ModQuad-Vi is a vision-based self-assembling modular flying robot designed to operate in outdoor environments. The drone modules dock in mid-air to form a larger flying machine.
As the researchers explain:
Our design is based on a quadrotor platform with onboard computation and visual perception. Our control method is able to accurately align modules for docking actions.
The above video gives you a better idea how this all works.
[Source]