Materials:
Nerf N-Strike Elite Stryfe gun (with clip)Servomotor with an X-shaped armSingle pole single throw (SPST) reed relayPassive infrared (PIR) sensor (with 9V battery)Roll of 22-gauge hook-up wireTripod¼-inch nut and washer
Tools: Phillips-head screwdriver, wire cutters, soldering iron Instructions: Diagram: Tips:
Insert the 9V battery into the PIR first and wait for the servomotor to stop spinning, then load a clip into the Nerf gun.Do not use fully loaded clips. Rather, insert only half the required number of darts for each clip capacity (e.g., three darts inside the standard six-dart clip).Once activated, the PIR has a refractory period of approximately two to five seconds during which time the sentry will not fire.Alignment errors with the servomotor can cause dart jams. Gently tweak your alignment until the darts are fed into the acceleration motor smoothly.Dart firing will be rapid and continuous until the PIR sensor no longer detects movement.
Approximate time to build this project: 4 hours Cost: About $65 Difficulty: 4/5 WARNING: These instructions will remove important safety features, could ruin the toy, and might even start a foam-dart arms race. _This article originally appeared in the May 2014 issue of _Popular Science.
