One of our first challenges as a small team was to build a cannon from Lego. This ended up being a little more complicated than we originally envisioned. We went through four different builds before we arrived at the final design.
Our first design relied on a large gear connected to our motor. Rubber bands could be stretched from the "aim" point at the front of the cannon to the large gear, onto which the rubber band was hooked to the teeth of the gear. However, the motor was not geared low enough to just leave the rubber band hooked to the gear without the tension of the band pulling the gear forward and thus releasing the band.
The second design did not go too far. Based on a crossbow, there was no easy way to put tension in the rubber band. While it would shoot a projectile, there was no catch or trigger mechanism, making it an unacceptable design.
Our third design was based upon an automatic baseball-pitching machine. As geared, the motors were not strong enough to launch a Lego more than three inches. Mitchel suggested gearing the motor with a large gear and the two wheels with a small gear. While this did increase the velocity of the wheels, the motors were still not strong enough to launch a projectile.
After puzzling over the issues we faced I decided to use Barb's suggestion of using a worm gear. By mounting the motor on its side I felt that we could interface a worm gear. Once the engine was moving it would unwind the rubber band and it would launch. However, the "drive train" on the motor isn't long enough to properly mount the worm gear. Back to the drawing board. By mounting the motor flat then adding a couple of gears I was able to transfer the drive of the motor from the horizontal axis to a vertical axis. Eureka! A little fine-tuning and we had a working cannon! This design also allows us to load three rubber bands onto the gear at a single time. It turns out that it makes a difference which direction the worm gear is facing: one way tends to make the third rubber band hang on the cannon. With all the bugs worked out we were ready for the Lego challenge! |
VirtCamp 2006 
Mitchel fine-tuning the original cannon design 
Josh sorting parts 
Benhaz and Heather arranging the Lego 
Benhaz, Margaret, Heather, Mitchel, and Barb post-Lego programming 
Despite crossing our fingers, the third design did not work to our satisfaction 
Back to the drawing board 
Gearing on the final design 
Final cannon design: lookout!! 
