There are a lot of people building their own sort of this thing.
Apparently it doesn't take much more than a power supply, a couple little motors for x/y control, and a power car door lock. camera is optional.
And for legal reasons, some may like to involve a raspberry pi that does some kind of counting to keep it in semi auto mode only. hooking the fire control group to a cam wheel that keeps turning while you have your joystick trigger pulled would be considered full auto.
for inspiration, just google insurgent remote control guns. there are some good examples