Often, the focus is on obstacle avoidance. With this bot, the obstacles are just accepted.
Drawing inspiration from watching insects repeatedly smack into objects rather than attempting to avoid them, then subsequently flying away unscathed, Przemyslaw Mariusz Kornatowski and Adrien Briod have come up with a novel approach to dealing with obstacles: simply smashing into them.
Adrien Briod holding the Gimbal.
In this picture you can see their robot, called Gimbal. The name clues you in to how it works. The simple locomotion and steering system is suspended within a gimbal, encased in a spherical frame. When the flying robot hits something, the outer frame may be whacked into motion, but the internals remain fairly uneffected. By choosing to simply ignore any kind of obstacle avoidance through sensors, they have greatly reduced the complexity of this task (navigating difficult terrain), in terms of both code and hardware.
A fantastic example of the power of this lies in the exercise they carried out in the forest. Nearly any other method of ensuring passage through a densely wooded area would have involved incredibly complex systems of sensing and navigation. The gimbal, however, just bounces off the trees with a steady course set for the other side. It may not be graceful, but it gets there!