Wouldn't it be ace if you could catch your housemate, coming home from a late night out? They tiptoe across the floor; then, from out of the darkness of the lounge, a red light, and a singsong voice: "I see you".
Engineering graduate Yvo de Haas -- Dragonator on Instructables, who has built gaming prop projects from both Portal and Fallout -- has designed a 3D-printable Portal Turret prop that can do just that. The device can track humans, aim and "fire" its guns -- but making a working turret isn't as easy as it might seem.
"The design was the hardest part of this project," de Haas wrote. "Not because there are no reference images or because the turret is that difficult in its design. It is because the turret does things that are not physically possible."
When he set about designing the turret, he wanted it to open and close its gun ports -- but he found that, with the ports closed, the guns left no room for anything else. There's also very little room inside for the electronics.
"After I built mine I did a last wave of improvements where I hollowed out the top of the turret," de Haas wrote. "There is some space there now to place electronics if you can manage to make them small enough."
Although the turret has servos and LEDs inside, it relies on a PC with a camera for motion tracking -- which it does by following a patch of colour rather than a body -- and it can be controlled by an external wired joystick.
The shell is 3D printed in 18 parts, and you'll need some knowledge of wiring and programming to put it together.
"The turret has been one of the more rewarding projects. It was a fairly small print with only 20 hours, it was quick to build and it has a surprising amount of functionality. It also has something that the GlaDOS lamp did not have, but was requested a lot afterwards: tracking," de Haas wrote.
"This time I had someone near me who was capable and willing to write the code to track a person. At this point I am capable of writing such a piece of code, but not in the short amount of time I had left before the deadline. Yes, both the firmware and software crash fairly often, but both do work."
If you want to take a crack at it yourself, you can find a detailed how-to on de Haas' Instructables page.