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.
Step 1: Design
I started out by creating a basic design in Sketchup. The robot was to consist of two segments, joined by a spine which could be extended or retracted. Each segment would have four legs with very sharp points as feet. To climb, the legs on the top segment would pinch together and the sharp feet would dig into the bark, securing the robot. Then the spine would be retracted, pulling up the bottom segment. The legs on the bottom segment would then grip the tree, and the top segment would release. Finally, the spine would extend, pushing the top segment upwards, and the process would repeat. The climbing sequence is somewhat similar to the way an inchworm climbs.
In my original design (show in the images above), all four legs in each segment were controlled by one highly geared down motor. I decided to ditch this idea for a few reasons. Firstly, I could not find the type of spur gear needed to mesh the legs together. Also, with all the legs linked together, the robot would have a hard time gripping uneven surfaces. Finally, I decided that the robot would be much easier to build if the motors drove the legs directly.
The other significant change I made from my original design was the way the spine worked. In my model, I used a rack and pinion type gearing system to extend and contract the spine. However, I could not find the necessary parts to build such a system, so I ended up using a threaded rod coupled to a motor to actuate the spine.