DIY Autonomous Anti-Mouse Sentry Turret

Figure 1: Autonomous Anti-Mouse Sentry Turret

Ben Katz participated in the “Bad Ideas” competition (held in Massachusetts) with a DIY project named Autonomous Anti-mouse Sentry Turret. This contest is all about coming up with some innovative projects which involve the application of engineering tactics. Apparently Ben did the same by building, testing and calibrating a device in just three days. Like the name itself suggests, it’s much like a sentry gun that is meant to fire at objects which are similar to a mouse in size.

Before proceeding with further details, it is important to note that sentry gun is a weapon that is usually used by the military that can automatically aim and fire at the target with the help of sensors. These are also popular amongst the video gamers and have been featured in various popular games like Team Fortress.

Coming back to the device, it uses a modified version of the project sentry gun processing code with a similar mechanism. He started the project by gathering components like:

Servos
Webcam
Lazy Susan bearings
Airsoft gun
Transistors
Diode
DC motor
USB cable

First and foremost he built a pan-tilt assembly with aluminium scraps wherein the tilt axis was supported by servo’s output shaft while the panning was backed by Susan bearings and servo in the centre. He also made sure to remove all the undesired parts of the gun like trigger, handle and other decoratives before using it.

Later he used a DC motor to control the gun and wired some NPN transistors in a parallel arrangement. Then he put a diode across the motor output and heat-shrinked the whole setup. After that he fitted the webcam beneath the assembly and spliced its wires to those of a USB cable. Now it was the time for some code modification that he took from the sentry gun project.

To make it work for his anti-mouse turret, he removed the stock firing code. Moreover he added a line that would turn the fire pin high. For the limits, the lower one was set to a moving object by default while the upper one was set to a mouse-sized object. In this way it would be able to ignore bigger objects.

So this device is actually a mini sentry gun except for the fact that it uses the feedback from the web to fire at its target. First the webcam captures an object and if it complies with the set limits, crosshair responds accordingly. If there is no object, it stays thin but as the target arrives within the range, the crosshair thickens and the object is boxed in a red pattern. Once the target is detected, the DC motor helps the gun in firing shots at the object.