This is my very first NXT project, and the idea was to build an automatic defence gun as a proof of concept and also to get myself familiar with building with the NXT and programming it.
I named my creation the Defender Mk I. This project is built on the premise of exploring how to build an elastic-powered gun using rubber bands instead of building a gun using the supplied parts in the NXT 2.0 box.
The Defender will scan using the ultrasonic sensor to the front of itself 50cm, with a coverage of 60 degrees for any objects that come within. If an object is within this threshold, it will engage it with its gun. The coverage parameters can be tuned in the code.
The rotating platform uses one servo motor, and the gun mechanism uses two. There were several design considerations and observations made when I built the gun:- The weight of the gun with the two servos at the rear made the gun rather unbalanced and I had to mount the gun further to the front to keep it balanced.
- A rail system had to be built and integrated into the barrel for the rubber band powered 'firing pin' to move back and forward smoothly.
- I had to use a rubber link for the two shafts that makes up the arm that holds back the 'firing pin' so that the arm would not slip and release the 'firing pin' prematurely as the rubber bands has quite a considerable amount of elastic power pulling the 'firing pin' forward.
