The Brick Experiment Channel (previously) built three different LEGO robots to climb a flagpole and a tree. The three different types were gravity locking, rubber-band locking, and a circulating climber. While there was a bit of scientific trial and error at first, these amazing robots eventually did what they were designed to do.
Demonstrating pole climbing mechanisms with Lego. All 3 machines are tested against a flagpole that is 8 meters tall, 13 to 8 cm thick, and ropes on the surface.
via The Awesomer