This is fantastic!
I bring a Weighted Companion Cube to Burning Man, and of course have thought about a few sentry turrets too. However, in my case, the most they would do is shoot water, or blow bubbles, which would make the overall mechanism a lot lighter.
Oh - also, my cube is a steampunkified, so I could probably make my legs out of regular table legs in my version of this, but given how much machining you're doing, it's making me think there's no way; I don't have access full time to that kind of equipment.
What size of mill / lathe would be required? I'm really tempted to get a Harbor Freight mini mill.