This is a
missable achievement if you want to unlock it through game play. It is unlocked when you find two additional pods and upgrade all three of your pods to the maximum level. Pods can be upgraded at the Resistance Camp, maintenance in the bunker terminal, or the special shop in the Flooded City Colosseum. You start with Pod A and find Pod C in the desert and fish for Pod B in the Flooded City. If you miss the achievement in normal game play (or choose not to pursue it), you can purchase it in the special achievement shop that becomes available after your third playthrough. It costs 100,000G.
Note: Make a save before fully upgrading the last pod in case of a glitch. The reason that the achievement is missable in normal game play is that each of the three pods requires a
Powerup Part S (for small). There are only three in the game. Two of them are acquired as rewards from side quests--Robo Dojo--Red Belt and Anemone's past. The side quests are not missable because they can be done with chapter select if not during a regular playthrough. The third Powerup Part S, though, is a drop from the stubby gold machine in the City Ruins that appears with two large Goliath gold machines. The Powerup Part S drop will always occur. However, if it is not picked up immediately following successful conclusion of the battle, it will be lost. This battle will not recur during chapter select.
Other rare parts:
Each pod requires a
Powerup Part M (for Medium) for the second upgrade. There are only three in the game. One is in the Forest zone on a ledge above the deep drop down to the river. One is in the copied city in a hackable chest. During your second playthrough, after 9S is rescued from the copied city, go back to the copied city and hack the chest. You do not control 9S in the copied city during the story so it requires a special trip. When you make the special trip,
make note of where you exit the elevator in the Copied City. Because of the uniformity of the landscape, it may be hard to spot when you want to make your exit. The third one is in the Flooded City resource recovery unit--the Soul Box. If you don't pick these up during normal game play, you can go back and pick them up with chapter select.
Each pod requires a
Powerup Part L (for Large) for the third upgrade. When you are at a high enough level to damage the large bronze statue in the amusement part, do so. Then defeat it. It is easier to defeat through hacking rather than combat but a high level character can defeat it through combat alone.
The large robot rabbit will always drop a Powerup Part L when defeated. If you leave the region and return or save and load the save file, the rabbit will respawn. Powerup Part L is only used for pod upgrades so you only need three during the entire game.
Edited 26 July 2021:
Shutdown observes in the comments that the giant rabbit no longer always drops the Powerup Part L and suggests finding the others required in the tower and in Emil's house after doing his last quest.
Pods B and C each require 10
simple gadgets for the first upgrade, 5
elaborate gadgets for the second upgrade, and 3
complex gadgets for the third and final upgrade. They are all rare components and the complex gadget is very rare. If you need extra items, the simple and elaborate gadgets can be harvested in the infant's cradle in the Forest Castle. There is an access point nearby. Save at the access point, check the cradle, and save if you find a useful item. Keep reloading this save until you have enough simple and elaborate gadgets. Bear in mind that quests will give you most if not all of what you need. Quests will give you five of the complex gadgets you require. Since they are very hard to find or harvest, I recommend that you pick up an additional 4 to make matters easier. During your second playthrough, accept the weapon's dealer quest, pick up the 4 complex gadgets he requires but do not turn them in to conclude the quest. This assumes that you have bought all the weapons you need from weapons shops during your first playthrough.
The other required parts are not considered rare and should pose no difficulty. In a comment to another achievement, a player mentioned difficulty with Pure Water. Pure Water is not uncommon in the Flooded City. Make a save at the Flooded City access point and harvest the items until you get what you need.
If the achievement does not unlock when you upgrade the last pod to the final level, you have probably experienced a glitch. In the event of a glitch, clear the cache. To do so, turn off the console by holding the
button on the console for at least ten seconds and then unplug the console for at least 20 seconds. Load the save you made just before fully upgrading the final pod. Clearing the cache will most likely remedy the problem and the achievement should unlock when you fully upgrade the final pod.