Generally, flying robots are programmed to avoid obstacles, which is far from easy in cluttered environments. At the Laboratory of Intelligent Systems, we think that flying robots should be able to physically interact with their surroundings. Take insects: they often collide with obstacles and continue flying afterwards. We thus designed GimBall, a flying robot that can collide with objects seamlessly. Thanks to a passively rotating spherical cage, it remains stable even after taking hits from all sides. This approach enables GimBall to fly in the most difficult places without complex sensors.