Instructables user Technochicken built this cool tree-climbing robot:
After I got comfortable programming and building with an Arduino, I decided to build a robot. I did not have any particular type in mind, so I wracked my brain (and the internet) for cool robot ideas. Eventually, somehow the idea popped into my head to build a robot that could climb trees. At first I dismissed the idea as beyond my skill level, but after further thought, and some time in Sketchup, I decided to take a shot at the challenge. This is the result of my efforts.
[Via Arduino]
