Alright, since I recall Bushi telling me spoilers should happen more often, I'll spoil it then for lulz.
There are 3 sentry guns: Machine Gun, Rifle and Rocket types. One sentry per player I think.
They can be upgradable up to 3 levels by using a welder, not a wrench
They can be controlled by a "controller" item which lets you maneuver/manual pilot the sentry.
Each level makes the sentry stronger.
The last item is the RC Bomb. It's basically a rc car with a C4 with it that can be controlled and when you right click it explodes. It's a bot too.