I don't understand why nobody has put auto-shotguns on an tripod with an aiming system, like a mini-CIWS.
I've seen Russian soldiers successfully shoot down drones using shotguns, the problem is that the smaller ones can be too fast and nimble for humans to reliably target. Even if you can shoot down 2 of 3, the third one will get you.
Combine the YOLO algorithm with a high-frame-rate camera, a two-axis servo, a heavy tripod, and a shotgun... and you're defended!
This could be mounted on the back of a tank or humvee also.
Something like you describe really does sound like an ideal terminal stage defense system, with 20 or 35mm autocannon covering longer ranges.
Purely theory crafting, I think the final piece would be small, standalone AESA radar units perhaps the size of a man-carryable generator that can be distributed across a given area and networked to likewise distributed shooters, spreading out the targets, adding redundancy to the system, and reducing the odds of your dugout-with-air-defense-asset getting hit by an anti-radiation munition that homed in on a known emitter.
The reason that you don't need radar for this is that the small suicide drones use cameras (vision) to attack. If you can't see them, they can't see you! Contrast this to general aviation where planes can be kilometers up, behind cloud-cover and can attack you with radar-guided missiles.
Radar probably won't have high enough resolution and won't be able to differentiate between drones and birds. Not to mention that most drones are carbon fibre or plastic and won't have much of a radar return to begin with.
Conversely, vision systems could be trained to ID drones reliably, and could use data such as the high-frequency "beat" of the propellers to detect drones from just a few pixels of sensor data.
Shotguns have a very limited effective range. Round pellets have a low ballistic coefficient and lose energy quickly. Using larger bore shotguns only delivers marginal range improvements. Automated shotguns might end up being one aspect of SHORAD, but based on recent developments it looks like they'll end up being less important than jammers plus autocannons (short term) and lasers (longer term).
I think many are trying something along these lines. The devil is in the details.
The shotgun needs to be reloaded. The system needs to be reasonably reliable and durable. Feels like the range of the shotgun is also a problem. The system needs to have some sort of friend vs. foe identification, possibly not shoot at birds or other random objects. The camera needs to be able to deal with looking at the sun and low light, day and night, likely needs to be able to scan. Pretty soon you get to: https://en.wikipedia.org/wiki/Phalanx_CIWS
My point was once you start adapting to all the requirements you inevitably end up with a more complex system. Another thing that happens in a war is that the enemy will adapt to what you're doing.
The principles are fine (well, not sure camera is the right only sensor but aside). The actual engineering of a working system you can use in real life is complicated and that's what many are working on.
A Phalanx_CWIS is overkill. Also, I suspected that the system received continuous upgrades throughout the decades.
Likewise, the Abrams tanks are cold war era tanks, but they are continuously upgraded that a modern Abrams tank isn't really a 1980 tank. Modernization is likely to remove some weight and make Abrams more survivable against drones, in response to the Russo-Ukrainian war;
I've seen Russian soldiers successfully shoot down drones using shotguns, the problem is that the smaller ones can be too fast and nimble for humans to reliably target. Even if you can shoot down 2 of 3, the third one will get you.
Combine the YOLO algorithm with a high-frame-rate camera, a two-axis servo, a heavy tripod, and a shotgun... and you're defended!
This could be mounted on the back of a tank or humvee also.