You can find this quest at Free Heap, which is located a good ways north of Daytower, past a small island with some Snapmaws. Petra is having some trouble with bandits, who are sitting on a pile of power cells that she needs to do some work. These bandits are located to the east of Free Heap, so head out of the village and as you approach the bandit camp, you might see some nearby Scrappers. They are actually important to this quest, but not until after you finish with the bandits.

Watch out for the two bandits by the arch; try to separate them and kill them one by one, then get to higher ground. Getting to higher ground makes this place a lot easier, as you should be able to get clean shots some quite a few bandits. Make sure you use your Focus to tag them, so you know where the bandits are at all times. Clear the first area, then move up into the second area, where you need to clean up the rest of the bandits. When the coast is clear, you need to find the Power Cells now. Two are on ground level and very easy to get, but the third is on top of a building. On the north end, find the small gap between the big building and the smaller one to see some handholds, leading you to the Power Cell.

Your next objective is to get to the Scrapper Den, but you receive an ominous message from a bandit as you leave the bandit encampment. Luckily for you, the Scrapper Den is right next to the bandit encampment, and your goal is to retrieve some weapon parts. They are all found in Scrapper piles, but there are quite a number of the machines in the area. However, by now, you should know that a good Shadow Sharpshot Bow with purple damage mods can instantly kill a Scrapper with a good shot to either weakpoint.

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You need to find some Power Cells at the bandit camp (left), as well as Weapon Parts at the Scrapper Den (right).

Go around and loot the weapon parts, then return to Petra, who finishes building the Oseram Cannon. It’s a good thing she did, too, as bandits will start attacking Free Heap. To use the cannon, hold down L2 and then hold down R2 to start loading it. This is indicated as a meter next to the aiming reticule, so when it’s to your desired length, let go of R2 to fire. The bandits attack from three different paths, in waves at first, then all at once. After a couple of rounds, you’ll be told to destroy the bridge, so try and aim at the ground in between the two arches. When successful, the quest will finally be over.