Blog Post from Luke Laurie’s Teacher Blog: http://lukelaurie.wordpress.com/
My son received an R2-D2 aquarium as a gift a while back, but we never had it set up with fish. After siting around for a while as a decoration, I got the idea of putting some mechanical and electronic components into it and turning it into a robot. After all, I teach a robotics science class, and have a lot of LEGOs and other parts lying around. By doing this work around my students, I could show them a thing or two about design and troubleshooting a robot project like this.
To start, I needed the thing to be able to move, and I decided that it would be most fun if he could be remotely controlled. So I got out some VEX robotics materials that were going unused, and set about designing a driving base to match the R2 shell.
I started with a design that had large enough wheels to be pretty quick, but could still carry significant weight. I used some LEGO wheels for the front, which worked OK, but they had to slide around when R2 turned, and would most likely get stuck on carpet. The rear wheels were also too large to fit inside the R2 feet, so they wouldn’t do.
Deciding that the rear wheels were two big, I switched to smaller wheels that had about 1/2 the circumference. If I attached these directly to the motor in the same way as the larger wheels were connected, my robot would cut its speed in 1/2. That would be too slow for my taste.
So I put a couple of gears on there- a larger one with about 60 teeth attached to the motor, and a smaller one with about 30 teeth attached to the wheel axle. Bingo- the robot speed was right back up to the same speed as with the larger wheels, I just lose a little energy and add a little noise because of the gears.