I wanted K-9 to have as many features as I could reasonably install. One feature that I'm particularly proud of is his fully articulating laser cannon nose. It moves in and out as well as pivoting enough to aim at aerial targets (or children that get too rough).

Two servos are controlled by an Arduino Nano. The larger of the two lifts the plate that supports the pvc "cannon" and the smaller servo moves the cannon in or out. An embedded command to play a particular MP3 accompanies the command to change the cannon's position. A high intensity red LED is glued into the cannon to provide a shooting effect. The majority of kids that meet K-9 look down the cannon's barrel so I didn't use a real laser. Also, some conventions do not allow laser pointers of any kind.