Building a Sentry Gun with Laser Trip Wire System and Arduino

*NOTE* THIS PROJECT IS DONE BY A GROUP OF STUDENTS FROM SINGAPORE POLYTECHNIC.

Concept:
Trigger gun when laser is blocked by intruding object.

Note:
Tilting is included for expandability but not used in this project.

Skill Level:
Basic soldering and basic metal works

Things You Need:
Toy Gun(Any will do, preferably a semi-auto)
Continuous Rotation Servo Motor
Servo Motor
Servo Arms and Wheels
Arduino
Metal Sheets
Ball Bearings
Bolts
Nuts
Screws
Rubber Washers
Cable Tie
Copper Wire
Copper Strip Board
Pins
Sockets
Resistors(1K Ohm)
Light Dependent Resistor
Potentiometer(20K Ohm)
NPN Transistor(2N2222)

Step 1: Building the Frame

Cut the metal sheets into 6 rectangular pieces(4 of equal length, 1 long, 1 short) and 2 square pieces.
Below are the dimensions we used:
4x 6”(inch) by 2”
1x 10.5” by 2.4”
1x 2.5” by 2.4”
1x 10” by 10”
1x 9” by 9”

Feet(6” by 2”):
Bend the 4 metal piece 90 degrees at the 2” mark and make  screw holes(at least 2) at the shorter end.
[Image 1]

Base(9” by 9”):
Make screw holes that match your feet’s at 4 corners of the metal piece to mount the feet and a hole in the center for the pivot(the hole size depend the bolt you’re using).
[Image 2]

Gun Support(10.5” by 2.4”):
Bend the metal piece 90 degrees at the 2” mark and the 6.5” mark to form a deformed U. Make screw holes(at least 2) at shorter end  and 4 holes at the other end to mount your servo.
[Image 3]

Turning Panel(10” by 10”):
Make screw holes that match the gun support’s at one corner of the metal piece and one hole in the center for the pivot(should be slightly larger than the pivot but smaller than your ball bearings).
[Image 4]

Servo Mount(2.5” by 2.4”):
Make a hole at one end to fit into the pivot and 4 holes at the other end to mount your servo.
[Image 5]

Step 2: Trigger of the Gun

Mount one of the servo to trigger the gun
We secure a small servo with a short servo arm onto toygun.

Step 3: Putting Everything Together part 1

Mount the gun onto a continuous rotation servo[Image 1].
Secure it onto the gun support[Image 2 & 3].
Secure another continuous rotation servo with wheels[Image 4] onto the servo mount[Image 5 & 6].

Step 4: Putting Everything Together Part 2

Read more: Building a Sentry Gun with Laser Trip Wire System and Arduino