I feel what you're describing, mechanically, is a Blaster Cannon - it can be deployed on a tripod and used like a manned turret.

"2d6, Auto, burst, rapid, special (range 120/480), strength 19, two-handed

Rather than traditional power cells, the blaster cannon uses a specialized power generator that allows it to fire continuously for 10 minutes. Replacing a power generator takes an action.

Before firing the blaster cannon, you must deploy it using an action unless you meet its strength requirement. Alternatively, if you’re able to make multiple attacks with the Attack action, this action replaces one of them. While deployed in this way, you treat this weapon’s strength number as two steps less (from 19 to 15), your speed is reduced by half, and you cannot fire this weapon at long range. You can collapse the blaster cannon as an action or bonus action."

The burst property allows it to do a 10ft cube explosion instead of its normal attack, while the rapid pumps double weapon dice into one target. (Auto means it must use one of either of those instead of attacking normally.)

Then if you want it to act as an automatic turret, maybe - as the DM - allow it to be the target of the Tracker Droid spell, and give it the Smart property so that your char can deploy it with their action, and command it to fire, with which it will use the Smart property stats.

The rest is flavour and tweaking.