Over on Instructables, I found a tree-climbing robot built by a high school senior. This is a great project, especially since it was done by someone with no formal engineering experience. The basic idea is a segmented robot with a front half and a back half, connected by a telescoping spine. Each half has four legs tipped with a sharp spike. The front half grips the tree with its legs, and the spine retracts, raising the back half. Then the back half grips, the front half loosens, and the spine extends, raising the front half. The front half grips the tree, and the process repeats, with the robot climbing sort of the way an inchworm does.
Most of the robot is built from a length of 3/4 inch x 1/8 inch aluminum bar. He cut, bent, drilled, and filed pieces of the bar to make legs, the frame, and various clamping bits. The linear slide that guides the spine is made from round steel bar and brass tubing. The original plans called for a rack and pinion to extend and retract the spine. In the end, he used a threaded rod to save money. He also repurposed a hard drive bearing as a thrust bearing for the threaded rod. An old laptop battery serves as the power source for the leg motors.
He used 7rpm DC gear motors to control the legs and another DC hobby motor to extend and retract the spine. The motor controller used three full H bridge L298 chips, and the overall control was provided by an Arduino. To be able to climb different sized trees, the Arduino samples the position of the legs. When it senses that they are slowing down, it assumes they have gripped, and it turns off the power.
I think this is a pretty good project. In fact, it has been entered in the Epilog laser cutter challenge over on Instructables. Thereís always room for improvement, however. In the case of this project, I think itíd be improved with a lot fewer screws, drilled holes, and filed grooves. Generally, make the thing simpler. Instead of attaching a T pin to the end of each leg to provide a sharp point, the point could be part of the leg material. Or the leg could simply be made from steel rod bent to shape and sharpened on the end.
It also would be nice not to have to use four gear motors to drive the legs. Instead of a motor per leg, a linear actuator could be attached to one leg and pull the other leg toward it, similar to the cable-operated brakes on a bike. The return action could be provided by the actuator, or simply by a spring.
Go to Instructables and take a look at the video.