Sentry Bot (Fallout 4)

A sentry bot is a type of robot found in the Commonwealth in Fallout 4.

Characteristics
The Commonwealth variants of the sentry bot are similar in overall appearance to the ones encountered in the Capital Wasteland and Mojave but are even larger (on par in height to a human wearing power armor and nearly twice as wide), appear to have a bulkier construction and are substantially more resilient. The typical weapons loadout of the sentry bot remains the same as seen in Fallout: New Vegas, with a missile launcher and minigun being the norm (except these miniguns appear to be unique 3 barreled variants chambered for the 5.56mm round). However, alternate weaponry configurations such as dual miniguns can also be observed. Annihilator sentry bots may also possess dual back-mounted mortar launchers, further enhancing their offensive capabilities.

On top of their already formidable ballistic and explosive weaponry, sentry bots now have powerful melee attacks and a self-destruct function with equivalent power to a mini nuke. Some variants appear to have four legs instead of three as seen in the previous versions. This may be due to the Commonwealth's rocky terrain requiring a greater amount of stability or its sheer bulk requiring a stronger propulsion mechanism to make it operable. They seem more durable than previous iterations of the sentry bot in other games, however despite being extremely bulky their mobility if anything has actually improved; they are capable of moving stunningly fast and traversing extremely rough terrain (even scaling rocky outcrops with little difficulty that the Sole Survivor would struggle to jump up on). In addition; a Sentry Bot's entire torso is capable of rotating independently of its legs, functioning akin to a turret and allowing it to move in one direction while shooting in a different direction (potentially against targets directly behind it).

A similar variant to the Commonwealth sentry bots can be found in Fallout: New Vegas at the REPCONN headquarters museum. Newer versions in Fallout 4 appear to use Mecanum wheels that allow it to strafe right and left without having to turn.

Gameplay attributes
Sentry bots are some of the rarest and the most difficult robots to defeat - fast, agile, heavily armed and resilient enough to absorb a direct hit from a mini nuke. After losing both main weapons they will initialize their self-destruct sequence and charge at the player character. Even with their ranged weaponry intact, sentry bots often charge into close combat to deliver powerful blows with their arms if one ventures too close, thus deterring attackers from any use of melee weapons. Since they explode on death with the force of a mini nuke, this tactic may prove even more dangerous to their opponent than their devastating long-range firepower. However, should a sentry bot engage the player for too long, they will eventually enter a cooldown period, blasting steam out of their back and exposing their dual fusion cores. Hitting exposed fusion cores is the best way to cause damage to them. Players having the Penetrator perk need not wait for cooldown, and can use VATS to target and destroy the fusion cores immediately. This makes this perk invaluable for fighting sentry bots.

Should one encounter a legendary sentry bot of any kind, keep in mind that all legendary robotic enemies explode upon death. This explosion does not override the sentry bot's in-built self-destruct, which means a legendary sentry bot will explode twice. Both explosions are equivalent to a mini nuke in power and occur with a short delay of a few seconds.

Sentry bots are a good if dangerous source of fusion cores, dropping at least two when they are destroyed, along with other valuable electronic components.

Low level players can defeat a sentry bot by hiding and running away until the sentry bot takes a few seconds to cool off, revealing its vulnerable fusion cores in its back. Firing any shot at them will instantly kill the sentry bot, however, the cool-down lasts only 2-3 seconds so one must act quickly. Even after destroying a sentry bot's fusion cores, it will still drop at least two of them. VATS can be helpful in targeting their fusion cores, due to the large amount of steam that sentry bots release when they enter their cooldown period concealing the cores, along with their small size.

Gunner sentry bot
These sentry bots are exactly like the original ones except the fact that they are responsive to Gunners and have a faded green tint, similar to a Mister Gutsy.

Siege breaker sentry bot
A higher and stronger variant of the normal sentry bot, these types can deal lots of damage towards their enemies.

Gunner siege breaker sentry bot
The same type of the siege breaker sentry bot, only it is only under Gunner command. They will attack anything that isn't a part of the Gunners.

Annihilator sentry bot
Tougher and stronger variant of the siege breaker sentry bot, these can deal lots of damage towards hostile enemies. Some of them are armed with missile lauchers too.

Gunner annihilator sentry bot
A Gunner variant of the annihilator sentry bot. These can be very powerful and are sometimes armed with missile launchers.

Sentry bot lament
The sentry bot lament is a sentry bot that has been modified by the Rust Devils to suit their needs. They may be found accompanying Rust Devil patrols throughout the Commonwealth.

Combat sentry prototype MkIV
An inactive combat sentry prototype MKIV can be found at the robotics disposal ground. Inside the shed near the entrance to the facility there is a terminal that has a holotape loaded. Initiating the holotape on the terminal activates the sentry bot outside, after which it immediately starts to patrol the area.

By ejecting the holotape from the terminal and using it in the player character's Pip-Boy the Sole Survivor can command the sentry bot to different locations in the Commonweatlh to clear of enemies, after which it will return to the junkyard. However, these locations are limited to nearby military sites. Once activated, the Sole Survivor can interact with it via the Robotics Expert perk to further the commands for it.

Locations

 * Northwest of Murkwater construction site and South of Suffolk County charter school is what appears to be a partially submerged power station, with only the pylon towers above water. If the player opens a door in the central pylon tower they will see a cinder block wall, with both a graffiti message that reads "YOU LOOK NICE TODAY!" and the same red skull decal used in Halloween decorations just beneath it. A sentry bot will spawn on the opposite side of the tiny building and start attacking the player. The surrounding towers are handy as cover. Probably like other sentry bots, this sentry bot is level-dependent, e.g. at player level 63 it is an Annihilator Mark II.
 * A sentry bot will attack the Sole Survivor after exiting the National Guard armory.
 * A non-hostile sentry bot is guarding the outside of Cabot House.
 * West of Somerville Place and East of Vault 95 is a sentry bot in a cage, guarding a locked storeroom. It will attack whoever picks the lock on the door or defend itself if attacked.
 * A sentry bot is guarding a shack west of Medford Memorial hospital.
 * A sentry bot will attack you at the top of the 35 Court building.
 * An inactive sentry bot is present in Hesters Consumer Robotics, which will immediately explode if attacked.
 * There's a chance of a sentry bot spawning near the highway between Easy City Downs and East Boston Police Station.
 * Two sentry bots attack the player after obtaining the Beryllium agitator in the Mass Fusion building.
 * It is unknown if it is a glitch or not but only one legendary sentry bot can be encountered instead of two normal variants. The second sentry bot will be destroyed inside the room where the legendary one came out of, with all its loot. This can sometimes occur with a non-legendary sentry bot as well.
 * An inactive sentry bot can be found in the Old Robotics section of the Institute. It can be activated with the robotics terminal. It will fight the synths that are on the assembly floor, but will also be hostile to the player.
 * At the Robotics disposal ground there is a sentry bot that is inactivated. It can be activated by using the Combat sentry proto MK IV holotape that is in a small building nearby.
 * Two can be found by and on the bridge south east of Lynn Pier Parking, there are also a assaultron and Mister Gutsy after passing the bridge.
 * Close to the South Boston military checkpoint, at a unmarked Red Rocket.
 * On the broken highway just west of Flight 1981 at a raider encampment.

Notable sentry bots

 * Ahab - encountered inside the Fort Hagen satellite array.
 * Ironsides - non-hostile protector of the USS Constitution in Last Voyage of the U.S.S. Constitution.
 * Combat sentry prototype Mk. IV
 * Gus - in a special encounter, non-hostile sentry bot that roams with the small merchant girl, Kat.
 * Sarge - encountered inside the armory of The Castle in the quest Old Guns.
 * A non-hostile sentry bot, outside Cabot House.

Automatron
With Automatron installed, the Sole Survivor can build their own sentry bots at any robot workbench. They can then be ordered to follow the Survivor like any other companion.

Owing to their sheer power, constructing sentry bots requires huge amounts of rare crafting components on par with upgrading X-01 power armor, high levels of the Armorer, Science! and Blacksmith perks as well as at least one point in Gun Nut and Robotics Expert each, assuming one wishes to access all available customisation options. A fully upgraded sentry bot boasts a very large health pool, heavy armor, decent speed, the most powerful long-range weaponry of any custom-built robot type in the game (up to and including twin Fat Man mortars mounted on its back) in addition to a very strong melee attack even without specific close combat weapons attached to it's arms, extraordinarily high carry weight and is capable of clearing out entire hostile strongholds on its own, given the right circumstances. On top of which; as ridiculous as it may seem (due to their immense weight) Automatron Sentry Bots are capable of manning guard posts at settlements (with the guard tower's staircase being just wide enough to accommodate them). This grants a settlement with a decent amount of open space for the Sentry Bot to maneuver a level of protection far out of proportion to it's supposed defensive rating and can potentially provide further assistance to any settlers during a raid if it is fitted with a support system granting damage resistance or health regeneration to allies.

As powerful as they are, the sentry bots' performance as companions suffers from a couple of drawbacks:
 * Their chassis is prone to overheating which often leads to temporary shutdowns in the heat of battle.
 * Despite their high health and heavy armor they tend to take a lot of damage very quickly, even when fighting rather weak enemies like raiders, which is largely owed to their immense size making them easy targets.
 * Although sentry bots can be outfitted with the widest array of unstable weapons, doing so is ill-advised as these guns are extremely fragile. The unstable Fat Man mortars usually break after just one shot whereas unstable miniguns or gatling lasers rarely get off more than two to three bursts before exploding, so mixing in some stable ranged weaponry may be a prudent choice. The sentry bot will automatically repair the weapons once the battle is over, yet it still creates several problems:
 * Any sentry bot without usable weapons will immediately initiate its self-destruct sequence, just like all completely disarmed robots do. An automatron that got swarmed by melee enemies and detonates in their midst is devastatingly effective, but should the robot carry ranged weaponry, it will usually try and stay close to the Sole Survivor, thus posing the hazard of killing its master in the ensuing nuclear blast unless points have been invested in the Inspirational perk.
 * Automatrons whose guns exploded cannot be repaired with robot repair kits during combat, which means they will instead self-destruct, take some time to reactive, then will often lose their weapons again very quickly and repeat the cycle. In comparison, robots with stable weaponry are usually much more effective.
 * Assuming they are armed with weaponry typically associated with other Commonwealth Sentry Bots (Miniguns, Missile Launchers, cluster launchers and gatling lasers) the Automatron Sentry will have a rather poor level of combat effectiveness against humanoid targets at long range (especially if they are in cover) due to the low accuracy at distant targets and or very short firing range of it's weaponry. This can potentially be alleviated by using a Robobrain Head to increase ranged weapon's accuracy or even fitting a Sniper Laser weapon.
 * Custom sentry bots are just as large and wide as any other exemplar of their kind (assuming they are using the sentry torso and legs), so they are severely handicapped when fights move into close quarters, especially indoors. This doesn't keep them from trying to follow the Sole Survivor, but since they tend to get stuck in doors and similar obstacles, they do so by teleporting to the Survivor's side, which in turn results in them completely blocking doors and hallways extremely often.
 * Contrary to most hostile sentry bots encountered in the Commonwealth, sentry bot followers seem to have serious pathfinding issues to the point where it turns them into sitting ducks on a regular basis.

Bugs
At the robotics disposal ground, the prototype sentry bot MKIV does not move once powered on. There are a number of fixes:
 * Fast travel elsewhere and sleep.
 * Using the Robotics Expert perk to disable and then reactivate the sentry bot.
 * Enter the console and click on the sentry bot, type, then.
 * If activated and it still won't move, deactivate either by hacking or the holotape (may say data corrupted), hit or shoot it once, then activate it.

Gallery
Робот-охранник (Fallout 4)