Background
Occasionally, the powers that be at Cornell decide that in addition to being badgered with problem sets, engineers should actually build something, too. Such was the case during the co-op summer session, when the "Rock Retriever" joined such infamous tasks as the torque wrench and the air motor on our project resumes.
The project was derived from the American Society of Mechanical Engineer's annual student design competition, in which well funded teams from around the nation develop entries over the course of several months. We were given the same project, a $100 budget, and about five weeks.
The Project
What the project actually consisted of was the design, construction, and demonstaion of a prototype rock retriever for a NASA mars mission, a la Sojourner. It would have to perform two trials in which it crossed three barriers at vairous angles, retrieved the rock, recross the course, and deposit the rock in a bullseye before returning to the starting postion. The entire system, including radio or umbilical controller had to fit in a specified toolbox and would be judged on vehicle weight, time, and accuracy of the drop.
We worked in teams of four and my group soon decided on a tank-like treaded vehicle with some kind of claw to grab the rock, all operated by remote control. Ithaca is quite the shopping anti-mecca, so there wasn't a single serious R/C or hobby store to be found. Thus we were forced to turn to the ubiquitous Radio Shack for cars we could strip for motors, servos, and controllers.
The Frame
The frame proved to be another challenge. While there was ample perforated peg board around the lab, we dismissed such low tech material while considering steel, 6000-series aluminum, and magnesium. But all those paled in comparison to our final choice: carbon fiber wrapped around a core of balsa wood for a light-weight, high-stength frame that couldn't be broken.
While we got some surplus carbon for free, knowledge of how to work with it wasn't so easy to come by. But after a weekend of experimentation and eight hour baking sessions in my apartment, we had a frame. We also took the opportunity to wrap some Xacto knives, flashlights, and other household items. (This is why you should be wary of subletting your apartment to engineers.)
The Guts
While the frame cooked, we came up with a gearing system and worked out the electronics. The frame was assembled using high-strength epoxy (we knew this was a high-quality product since it said "two-ton" right on the box). Onto the frame we attached the control cicuitry, axles, gears, and the claw.
Besides the carbon fiber frame, the claw is one of the unique highlights of our design. It came in a flash of inspiration while walking past Claire's in the mall: why not use a hairclip? After the rather comical event of four college guys buying a hair clip, we cut, heated, and shaped it into a claw capable of grabbing an inch and a half sized rock. With generous amounts of epoxy, it was mounted to a servo and hung off the front to serve as it's namesake.
Days and Nights of Reckoning
Testing out our creation revealed a variety of problems, ranging from electronics problems to power drain issues to the inability of the tracks to stay on. We tossed the radio control in favor of a staight forward umbilical cord, spent a small fortune to keep the batteries fresh, and added the gleam of aluminum tread guides to the black weave of carbon fiber on the frame.
For the competition, we demonstrated our usual inconsistent performance, but did complete the course, albeit peicemeal. We did have one of the lightest vehicles in the field, and certainly the most creative grabbing mechanism.