In the past few months, we have covered drones and robots being controlled using a heads-up display. L1Ranger has shared a guide that shows you how to how to control a Nerf Vulcan sentry gun using a Recon Snow2 HUD. For this project, you are also going to need UVEX G.GL9 Ski Goggles or something similar.
As you move your head, the gun also moves to keep up. The code and other info about this project are available on Instructables.