If you play Fallout 4, you may have discovered the shack called the Electrical Hobbyist's Club. It's surrounded by high levels of radiation. Chances are you will have to use a Hazmat suit to go into it. There's a nice laser rifle up here, so it's well worth checking this place out. As you loot the top floors, you will discover there's a cellar.
Watch your steps as you enter the cellar. First notice the bobby trap at the bottom of the steps. It will fire a rocket from a missile launcher if you set it off. Disarm it. That's the A button for XBOX players. Directly left is weight scale. That will set off the Legendary Assaulttron who will likely kill you since there's very little room to manuever down here. Worse yet, if you destroy it, the thing will set off an alleged nuclear explosion. I say alleged nuclear because I've just found a way to survive the explosion. Disarm the scale. Mr. Assaultron stays asleep.
But first, let's disarm the remaining traps. There's a trip wire in the terminal room. Directly to the left of the door to this room is a turret. I disarmed a trap to the right of the door. Ran back outside. To the left of Assaultron, is a hole in the wall. I took out my sniper and shot at the turret to destroy it.
Okay, let's get to the point. You want to destroy the Legendary Assaultron without killing yourself. Go back to the stairs. Take out your sniper and shoot at the thing until it's down to little health. It starts to catch on fire. Check V.A.T.S. to examine its health. Take out two fragmentation mines and put them around it. Go to the terminal room. Access the terminal. Activate the Assaultron. Go to the corner away from the hole in the wall. That's the corner next to the terminal. The Assaultron will move and set off the mines. It dies and explodes. You survive. At least, I did.
Loot the body. Since this is a Legendary Assaultron, there will likely be a nice reward. I got the Quickdraw Revolutionary Sword. It has 22 damage and its speed is medium. More importantly, it "Costs 25 percent less Action Points." I'm sure this is worthwhile to you players who prefer a melee build for your character.