A weapon upgrade is a permanent change to a weapon that automatically occurs upon gaining enough experience by collecting nanomites from defeated enemies in the Ratchet & Clank series. Collecting enough experience will cause a weapon to 'level up', often gaining more power, a higher fire rate or a higher maximum ammunition count. Eventually with enough levels a weapon will upgrade into an improved version, changing the design and significantly improving the way it acts in combat.
Ratchet & Clank (2002)
Ratchet & Clank (2002 game), being the first game in the series, features only a simplified version of weapon upgrading. It is not possible to earn experience and instead Ratchet can only upgrade his weapons in the Gold Weapons room. Gold weapons act as a predecessor to the weapon upgrades seen in later games, as they do not truly change the weapon's appearance besides changing their color to gold, though they do affect its functionality. Plus not all weapons had a gold version available, such as the Taunter, Walloper, or R.Y.N.O..
Typically the gold weapons room is found for the first time you visit Tobruk Crater, Novalis in challenge mode, as a new teleporter can take you there from your ship's landing pad. There is, however, a hidden version available in normal mode of the room on the Gemlik Base that sells only five out of the ten available weapons (in particular: Suck Cannon, Bomb Glove. Glove of Doom, Mine Glove, Decoy Glove). Said hidden room is located inside the tall tower at the end of the area, next to the landing strip Qwark uses to take off for his bossfight. Simply wall-jump to the top of the tower to reach the room.
Going Commando is the first game in which weapons could level up and automatically upgrade into an improved version. Defeated enemies automatically release nanomites which the weapon used to kill them will absorb. Enemies encountered late in the game drop more nanomites than those fought early on, whereas bosses will release the most instead compared to normal enemies. As such, weapons available later in the game will require more nanomites to upgrade as well. Once upgraded a weapon will physically change, gain improved stats and functionality. Each weapon could only level up once, except Gadgetron Corporation weapons, which could not absorb nanomites at all.
In challenge mode it is possible to purchase Mega upgrades for each fully upgraded MegaCorp weapon from MegaCorp vendors. Despite not being able to absorb nanomites to upgrade, there are also Mega upgrades for the Gadgetron weapons, except the RYNO II, that can be puchased from the vendors. Mega weapons are required to make outdated early-game weapons from normal mode once again available for competitive use in combat. Each mega weapon, except the Mega Gadgetron weapons, can then be upgraded once more through the action of absorbing nanomites, turning it into an Ultra weapon.
Up Your Arsenal
Up Your Arsenal furthers expands on the weapon upgrade system seen in Going Commando. Each weapon now starts at V1 and can be upgraded four times, from V1 to V2, V3, V4 and finally V5. Each weapon increases in damage with each upgrade, with some gaining a bigger ammo capacity and increased functionality resembling weapon modifications, such as the ability to lock-on, ricochet bullets or the equivalent of the shock mod. Lastly weapons could also change slightly visually though the V5 upgrade is when the major visual change occurs. At V5, as with Going Commando, it will gain even more ammo capacity and damage and furthermore change the weapon's functionality.
In challenge mode a Mega upgrade can be bought (if the V5 upgrade has been attained), upgrading the weapon to V6. From there it can further upgrade two more times to a Giga (V7) variation and the final Omega (V8) version. As before, each upgrade further increases the damage and ammo capacity though no longer imparts functionality changes.
In Deadlocked weapons start at V1 and can be upgraded all the way to V10 in a regular playthrough. Each upgrade increase the damage, though nothing else will change until the last one, which changes a weapon's name, design and improves its functionality. New to Deadlocked are alpha mods, stat-enhancing modifiers that can be equipped on alpha mod slots in each weapon. Weapons start out with one slot, and unlock more slots with each upgrade, each slot also comes pre-installed with a free alpha mod which can then be interchanged with other weapon's alpha mods.
In challenge mode a weapon's Mega (V11) version can be purchased (given the V10 version is available) and then upgraded all the way to V99, increasing damage along the way but without imparting new slots for alpha mods.
In Going Mobile each weapon starts at V1 and can be upgraded to V2 and lastly V3. Weapons started at V1 and could be upgraded twice to V3 through the use of nanomites. Each version increased the weapons ammo capacity and damage. They did not get any new functionalities and they did not change their names when they reached V3.
In Ratchet & Clank: Size Matters weapons could only be upgraded from v1 to v4 whereupon they upgraded to their more powerful version. In challenge mode, the Titan version could be bought, which reset the upgrade count to V1, allowing the weapon to be upgraded to V4 once more, though no new upgrade or notable change is acquired upon doing so.
Secret Agent Clank
Secret Agent Clank features an identical system to Size Matters. For Clank, Proto weapons could be bought, while for Ratchet, Titan weapons (returning from Size Matters) could be bought.
Tools of Destruction
Tools of Destruction retains a simple upgrade system, reminiscent of Up Your Arsenal. Weapons can be upgraded from V1 to V5, at which point they change into a more powerful version. Challenge mode allows the purchase of Omega (V6) versions of fully upgraded weapons, which then upgrade to V7, V8, V9 and finally VX (V10).
Quest for Booty
Quest for Booty copies part of the Tools of Destruction system. Weapons all start at V3 and end at V5 at which point they upgrade as normal. There is no omega version, as there is no challenge mode. The Alpha Disruptor is the only weapon that already comes fully upgraded upon being acquired.
A Crack in Time
All 4 One
Weapons don't upgrade from usage. Instead, upgrades for weapons could be purchased. There are three types of upgrades. Ammo, Power, and Elite. After purchasing a weapon, only the Ammo and Power upgrades could be purchased for it. After both upgrades are purchased, the Elite upgrade becomes available.
Full Frontal Assault
Weapons started at V1 and could be upgraded four times to V5 through the use of nanomites. Each time a weapon upgraded, its damage increased along with one other statistic, including, but not limited to rate of fire, range, or ammo capacity. At V3, the weapon would have a change in name and appearance.
Before the Nexus
Into the Nexus
Weapons started at V1 and could be upgraded two more times to V3 through the use of nanomites. Each time a weapon ugrades, it's damage increased along with other statistics, including, but not limited to rate of fire, range or ammo capacity. At V3, the weapon would have a change in name and appearance. In Challenge Mode, Omega versions of weapons (V4) could be purchased if the weapon was upgraded to V3. Omega weapons could be upgraded two more times to V6.