How to Get Sergeant RL-3 in "Fallout 3"by K.C. Moore ; Updated September 22, 2017
The Capital Wastelands of "Fallout 3" tends to be a lonely and dangerous place for the lone traveler. Fortunately, the game features non-playable characters that can be recruited to join your main character on his journeys, offering an extra level of protection. Sergeant RL-3 is a robot companion and one of several characters that can join you on your quest. Sergeant RL-3 is a Mr. Gutsy model of robot, which means he has the same built-in Flamer and Plasma Gun weapons as other Mr. Gutsy robots that you encounter in the game.
Search the wastelands for a man named Tinker Joe. He is found in the areas around the RobCo Factory and between the factory and Tenpenny Tower. If you have already traveled to these locations, use fast travel to immediately take you to the RobCo Factory.
Talk to Tinker Joe to see if you can purchase Sergeant RL-3 from him. You will only be allowed to do so if your Karma is at neutral. Check your Karma rating on your Pip Boy before attempting to recruit Sergeant RL-3. Neutral Karma means your character has performed an equal amount of both good and bad deeds.
Purchase Sergeant RL-3 from Tinker Joe for 1000 caps. He now automatically follows you around until you dismiss him.
If you ever become separated from Sergeant RL-3, he will be waiting for you in Canterbury Commons. After you have recruited Sergeant RL-3 you can raise or lower your Karma rating without losing him.
If you attack or kill either Tinker Joe or Sergeant RL-3 before recruiting him, you will not be given another opportunity to do so.