“With the Robotics Expert perk, you do an additional 25% damage to any robot. Also, sneaking up on a hostile robot undetected and deactivating it will put that robot into a permanent shutdown state.”— Fallout 3 in-game description
One can reprogram the mainframe in the mobile base crawler to have the security robots attack the Enclave instead of the Lone Wanderer. There is an additional dialogue with Stiggs where he tells about this when first entering the room.
Deactivating a robot awards 10 XP (Fallout: New Vegas only).
A deactivated robot cannot be targeted in V.A.T.S. However, the unit can still take damage, and destroying one will give the same experience and loot as normal. Every attack on a deactivated robot while sneaking will register as a "sneak attack critical," regardless of the player's location or level.
Making contact with a deactivated robot while sneaking may still alert other robots in the vicinity to the player's presence, just as if the robot were fully active.
When given the option to disable a sentry bot, it also gives the option to "talk" to the robot, as if one was interacting with a friendly robot, such as Wadsworth. However, one cannot engage the robot in conversation.
For deactivating a robot using the perk, it is sufficient to be crouched and behind it. As opposed to the perk's description, it is not necessary to be [HIDDEN], i.e. close up and unnoticed. The player character can in fact charge a hostile robot, crouch, circle strafe and disable it while it is circling about weapons blazing.
Automated turrets are scripted as robots and can be disabled with this perk. While in many cases they are out of reach, ceiling-mounted turrets can be disabled if the player is able to reach them by jumping while crouched.
When sneaking up on a robot with this perk, if "talk" is selected, it talks to the player character and does not attack. (e.g. a sentry bot, when the talk selection is selected, it will say "Do not interfere with security operations.")
Hacking a robot can be done in combat, but cannot be done at long distances.
When powering off a robot, the player character can still initiate a self-destruct immediately after without having to re-hack it. This will not reactivate the robot; it will stay where it is until it detonates.
Initiating a self-destruct will take some time. The robot will still continue to attack the player even as it begins the countdown to destruction; moreover, it will emit a small dosage of radiation. It is advised to shut down before initiating self-destruct.
Legendary protectrons will explode when killed; when combined with the self-destruct explosion, the player character should flee to a safe distance to avoid being killed.
Turrets and such cannot be hacked by this perk, and in fact require the appropriate Total Hack perk magazine to do so (via a terminal).
Robots such as sentry bots and assaultrons will act like a personal companion until they are killed. (The player character needs rank 3 of this perk to get full access to this.)
Hacked enemy robots will turn hostile towards any friendly settlements when following the Sole Survivor, but any hacked friendly robots will not attack them.
A robot that the Sole Survivor commands with the Rank 3 perk will follow and enter a different cell (i.e. entering an interior door) and will also fast travel.
To make a robot commanded with the Rank 3 perk stop following the Sole Survivor, just hack another robot.
Synths and all variants cannot be hacked with this perk, instead, one requires the Wasteland Whisperer (for Gen 1 & 2) and Intimidation (for Gen 3) perk to hijack them since they are classified as humanoid enemies.
It is not recommended to hack Percy in Diamond City and use the command option. This will cause him to follow the player character as a companion, potentially getting him killed. There is no way to make him go back to Diamond City permanently.
Rank 2 of Robotics Expert gives a 40% damage bonus against robots and synths, however, it is conditioned to stop working if you have rank 3.