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Most of the information in the first part of the article is general and applies to all mechs, however, Clan mechs have differences which are covered in their own section near the end.
Outfitting Constraints
There are several constraints to how much stuff (weapons, engines, armor, equipment, etc.) you can fit on a mech. Some of these are hard constraints--those inflexibly enforced by the game mechanics (such as weight). A few are soft constraints--these are constraints that aren’t explicitly enforced by the game but which have a significant impact on match play (heat efficiency is an example).
Hard Constraints
The first hard constraint is weight. All mech chassis have a fixed maximum weight, in tons, that they cannot exceed. This weight also classifies the mech into a weight class (Lights 20-35t, Medium 40-55t, Heavy 60-75t, and Assault 80-100t). All critical slot items and armor have an assigned weight, and the total weight of all installed items and armor cannot exceed the maximum weight for that chassis. There is no prohibition on being underweight, but this has no gameplay effect (e.g., an underweight mech moves no faster that a fully outfitted mech) so in practice being underweight should be avoided.
The second hard constraint are critical slots. These represent physical space within the mech where items can be installed. Except for armor and modules, all things installed on the mech fit into one of more critical slots, and each critical slot can can only contain one (or part of one) item.
Every mech has 78 critical slots, regardless of the size of the mech. These slots are divided into seven sections: the head (6 critical slots), center torso (12), right and left side torsos (12 each), right and left arms (12 each), and legs (6 each).
The third hard constraint are weapon and equipment hardpoints. There are five types of hardpoint: Ballistic, Missile, Energy, AMS, and ECM. Each of these five types of item can only be installed in a mech section with the correct hardpoint for that item. Each item takes up one available hardpoint of the relevant type when it is installed, regardless of the item size. Hardpoints are assigned to a specific mech section (though never the legs), and the type and number of hardpoints vary from mech to mech. It is possible to have multiple hardpoints of one or more types in a single mech section.
The fourth hard constraint is armor allocation. Every mech section has a cap on the amount of armor which can be installed to cover that section. This amount varies by mech weight (e.g., two 45 ton mechs have the same armor capacity). For the head, arms, and legs, this cap is a simple limit. However, the center, left, and right torsos work differently--while these sections have an armor cap, that cap is shared between the front and back of the mech. The armor assigned to the back of the mech reduces the amount available for the front and vice versa.
The fifth hard constraint is engine size. Each mech has a lower and upper limit on the size of engine that the mech can carry. The smallest engine size is 100 and the largest is 400. This limit applies equally to standard and XL engines. Larger engines let the mech move faster, increase torso twist speed, and may include bonus heatsink slots.
The sixth hard constraint is Jump Jet capacity. All mechs are assigned a value for the number of jump jets they can equip. In most cases this number is zero as most mechs cannot carry Jump Jets. For mech models that do, those mech may install a number of Jump Jets up to the limit of that chassis (or none, at the player’s discretion).
Those are the hard constraints enforced by the game. There are also what I call soft constraints--constraints that aren’t enforced by the game but which have a significant impact on mech performance and gameplay.
Soft Constraints
The first and most important soft constraint is heat efficiency, that is, the amount of heat a mech generates and how effectively the mech can cool off. Heat is a complex topic and has its own article. For the purposes of mech customization the player should be very mindful of how much heat is generated by their outfitting choices (primarily weapons) and make sure they have a plan to manage it. Briefly, the three main options are to generate heat and run away to cool (requires speed), add cooling capacity (requires critical slots), or have available weapons with low heat generation (such as Ballistics). In practice, all mech will use a combination of these strategies but certain mech designs are biased towards one or the other.
The second soft constraint is speed. Speed is simply a function of engine size--the larger the engine the faster the mech. The top speed of a particular mech is capped by its engine size constraints. Speed is very important in MWO for a number of reasons. A fast target is harder to hit than a slow one. Also, speed allows you to react to changing conditions, extricating yourself from trouble or moving where you are most needed.
The third soft constraint is ammunition. Missile and Ballistics weapons require ammo which when expended renders the weapon useless. Too little ammo and the associated weapon loses utility. Too much and space is wasted and the chances of ammo explosion increases (see the damage article for more information).
Minimum Fitting Requirements
There are certain items which a mech must contain to be considered valid for entry into a match.
First, there are critical slot items automatically included in all mechs. Examples are the cockpit, gyro, leg actuators, and so on. These items are fixed and cannot be moved or removed from the default locations. These default critical slot items consume critical slots and there is a hidden weight cost for the internal structure of the mech (equal to 10% of the max mech weight). So before any customization the mech has allocated 25-33% of its available weight and about 20 of the 78 critical slots to required items and internal structure. The actual numbers vary from mech to mech as the weights are different depending on weight class and not all mechs have all possible arm components.
Second, a mech must have an engine installed.
Third, a mech must have a total of 10 heatsinks. As is covered in detail in the article on heat, all engines have a number of built-in intrinsic heat sinks (this information is not available in game). If the installed engine has fewer than 10 intrinsic heat sinks the game will warn you and prevent you from using the mech.
That is all that is required by the game to enter a match--armor, weapons and equipment are optional (but recommended).
Engines
As mentioned above, all mechs must have an engine installed to be valid. Every engine has a size number, ranging from 100 to 400. The larger the number, the larger (and faster) the engine. Each variant of each chassis has a specific range of engine sizes it can equip. Engines are also subject to the larger fitting constraints of space and weight. All engines must be installed in a mech’s center torso, where they take 6 critical slots (XL engines also take up space in side torsos, as is explained below).
Engines come in two varieties, standard and XL. Except for some fitting and damage effects, standard and XL engines of the same size number have the same performance. The difference is that XL engines weigh less at the cost of additional critical slots, e.g., a mech with a standard 200 engine moves as fast as one with a 200XL engine, however the latter has more weight and less critical space available for additional items.
The effect of the engine on mech speed is a factor of the engine size and the mech’s maximum weight. For example, a 250 standard engine will propel a 40t mech more slowly than it will a 30t mech.
Engine size also affects torso twist speed.
All engines have between six and ten intrinsic heat sinks, depending on the engine size. These intrinsic heat sinks are not shown by the game but are counted towards the 10 heat sink minimum. Installing the Double Heat Sink upgrade also upgrades these intrinsic heat sinks. Engines larger than 270 also provide between one and six internal heat sink slots. These internal slots allow the installation of additional heat sinks without consuming critical slots on the mech. The weight of heat sinks installed in these slots is still counted. Both internal and intrinsic heat sinks do not take damage, but are destroyed with the engine (which destroys the mech).
XL engines take more critical slots than standard engines (but weigh less). In addition to the six center torso critical slots taken up by a standard engine, Inner Sphere XL engines take three additional critical slots in each side torso. Clan XL engines only take up two critical slots in each side torso.
At the moment, engines do not take damage from the critical hit system (see the damage article for more information of critical hits). Inner Sphere engines are destroyed when any section containing the engine is destroyed. This means XL engines are destroyed with the side torsos, decreasing the durability of XL-equipped mechs. Clan engines are destroyed when the center torso or both the side torsos are destroyed--a Clan mech can survive losing one side torso with an XL engine. Currently, losing a side torso reduces the heat efficiency of the Clan mech, but additional penalties for this damage type are planned.
Upgrades and Modules
Upgrades and Modules are additional ways a player can customize a mech that don’t involve adding items to critical slots. Each has its own menu in the games mechlab.
Upgrades are a set of paired options that change aspects of the armor or items installed on the mech. A player can choose one of the two options for each upgrade, and switching between them has a cost in C-Bills (even if the change is a downgrade).
Armor: Standard and Ferro-Fibrous
Armor comes in two varieties: standard and Ferro-Fibrous. Standard armor weighs 1/32 of a ton per armor point. Ferro-Fibrous armor is 12% lighter, at 1/36 ton per armor point. The protection of each is the same, that is, a ton of standard armor provides equal protection to a ton of Ferro-Fibrous armor (the Ferro-Fibrous armor just weighs less). The heavier the mech, the greater the benefit as larger mechs carry more armor.
Installing Ferro-Fibrous armor reduces the available critical slots on the mech by 14. These 14 ‘dynamic armor slots’ will automatically move to any free slot as items are installed, but the player is required to leave space for these 14 dynamic armor slots.
Dynamic armor slots do not have a further effect. They cannot be damaged or critically hit.
Internal Structure: Standard and Endo-Steel
Internal structure represents the framework, or bones, of the mech. Like Ferro-Fibrous, Endo-Steel structure saves weight at the cost of 14 floating ‘dynamic structure slots.’
All mechs have a hidden weight cost for the internal structure of the mech equal to 10% of the total maximum mech weight. For example, on a 50-ton Centurion the internal structure weighs 5 tons. Installing Endo-Steel reduces this internal structure to 5% of the mech maximum weight (so 2.5 tons for the Centurion). As mentioned above, Endo also consumes 14 critical slots on the mech. Dynamic structure slots do not have an additional game effect--they cannot be destroyed or critically hit.
Endo and Ferro-Fibrous can be taken on the same mech--this consumes 28 critical slots.
As a rule of thumb, Endo provides a greater weight savings than Ferro-Fibrous and should be taken first.
Heat Sinks: Standard or Double
Heat sinks are covered in detail in the article on Heat.
Missile Guidance: Standard or Artemis
The Artemis IV Fire Control System is covered in the article on Missiles.
Modules
(I’m not covering each type of module in detail, though that might be an article down the road)
Modules are upgrades that do not require critical slots and which have no weight. Each mech has four types of module slot: Consumables, Mech, Weapon, and (when the Mastery skill level is unlocked for the chassis) a Mech/Weapon slot. The number of each varies per chassis, but each will be at least 1 but no more than 3. 2 is the most common number.
Consumables are, as the name suggests, single-use modules that provide a benefit during a match, such as instant cooling or calling in an airstrike. They much be repurchased after use. Consumables do not require a skill to be unlocked in the skill tree, but there are skills that boost the effect of consumables.
Mech modules are items that provide a boon or special ability to the mech, for example, a longer targeting range or the ability to detect nearby mechs when you are standing still. Before a mech module can be installed, an associated skill must be unlocked in the Pilot Skill Tree. The associated module can then be bought for C-Bills and installed on any mech.
Weapon modules, like Mech modules, each have a skill that must be unlocked on the Pilot tree before they can be used. Weapon modules provide (currently) either a range or cooldown/rate-of-fire boost to a specific weapon type. This boost is very specific, e.g., there is a skill+module for LRM5s, and a separate one for LRM10s.
The Mech/Weapon slot is a bonus module slot unlocked when you have reached Mastery level on that chassis skill tree. It can be used to install either Mech or Weapon modules.
Clan Omnimech Customization
All Clan mechs currently in MWO are Omnimechs. Omnimechs share most of the same fitting constraints as non-Omnimechs but outfitting works somewhat differently. For the purposes of this section I am going to treat “Clan mech” as equivalent to “Omnimech”.
Clan mechs differ from Inner Sphere (IS) mechs in that several critical slot items which are customizable in an IS mech are fixed in an Omnimech. The most important of these is the engine--Omnimech engines are fixed in size and are always the XL type. An omnimech may also have fixed heat sinks or (rarely) weapons.
Most upgrades (Ferro-Fibrous armor, Endo-Steel structure, Double heat sinks) are fixed and cannot be changed. The exception is Artemis. Clan versions of these upgrades are smaller than their IS versions and take fewer critical slots (Ferro and Endo consume 7 versus 14 critical slots, Clan DHS take 2 vs. 3 crit slots). Clan Ferro-Fibrous is lighter than the IS version, at 1/38 tons per armor point (versus 1/36 for IS). Clan Endo-Steel and Ferro-Fibrous do not 'float' like the IS versions. They are fixed to specific critical slots on the mech.
C.A.S.E does not exist as a critical slot item on Clan mechs. Instead, all eligible sections of the mech have C.A.S.E. as a weightless, slotless upgrade.
The biggest difference between Clan Omnimechs and IS mechs is the Omnipod mechanic. On on Clan mech, the mech’s internal subsections (head, torsos, legs, arms) are not fixed and can be removed and installed on another mech of the same chassis as the donor. These swappable subsections are called Omnipods. The only fixed omnipod is the center torso--that omnipod defines the variant type of the mech and cannot be removed. Omnipods can only be exchanged between variants of the same mech chassis and can only be fitted to their original location (i.e., a left arm omnipod cannot be exchanged for a right arm pod and an Adder Omnipod cannot be fitted to a Kit Fox).
An Omnimech must have Omnipods fitted to all available locations to be valid for use in a match.
All qualities associated with an Omnipod are carried with it to its new location on a different variant. The most obvious examples are hard points--with Omnipods it is possible to somewhat customize the number of location of hardpoints on the mech, something IS mechs cannot do. Fixed equipment, such as heat sinks are also carried with the pod to the new location.
Certain traits, which on an IS mech are assigned to the mech as a whole, are divided among a Omnimech’s Omnipods. An example is the number of Jump Jets a mech can equip. On an IS mech, that number is a simple count for that chassis variant. On an Omnimech, that total number is divided and distributed to a number of Omnipods. For example, a Timber Wolf S can equip up to 4 Jump Jets. Two of this capacity is assigned to the right torso Omnipod and two to the left. If one of these side torso Omnipods were moved to a different variant, that variant would gain +2 Jump Jet capacity. The Omnimech’s quirks are also divided among a number of pods and carried with the pod when swapped.
Once the omnipods have been fitted to a variant, outfitting works much the same as on an IS mech.
General principles of mech customization
An ideal mech should take the largest engine, maximum armor, the heaviest weapons and enough heat sinks to fire those weapons continuously. This is not possible, of course, and deciding where to compromise is the heart of the mech customization part of the game.
The tips below are only meant as an overview for new players, not a guide to optimizing a particular class.
- Speed is life: It is tempting to compromise on engine size to fit more weapons on a mech, but in MWO speed means survivability and thus getting to use your weapons longer.
- Always use maximum armor: Many mechs by default have less than the maximum armor. You should always maximize armor on the mech and then trim back if you need a little extra tonnage.
- XL or not?: XL Engines make the mech more vulnerable to destruction, but offer an attractive increase in free tonnage. While there are no absolute rules, it’s generally safer to take an XL on a light mech and not on an Assault, where for Mediums and Heavies the decision is taken based on expected role (brawler vs. support) and hitboxes.
- Jump Jets and ECM should almost always be taken on mechs when they are available.
- Heat efficiency is generally more useful than up-front damage.
- It’s generally better for a mech to do one thing well than many things poorly. Smaller mechs are forced to be specialists but even assault mechs can benefit from picking one or two roles to excel at.
- The converse of the last tip is that battles are fought at all ranges. Consider the effectiveness of your design if you are dropped on a small map, dense with cover, or a large map with little cover.
This is one of a series of articles on concepts in MWO. If you found this article helpful, you may wish to read the other articles listed in this post.
Edited by Gauvan, 02 December 2014 - 12:53 PM.
