Internal Structure

Overview
The Internal Structure of a BattleMech forms the skeletal structure of the 'Mech to which all components are mounted.

The Standard Internal Structure of a 'Mech weighs 10% of its max. tonnage (i.e. on a 100 ton Atlas the internal structure weighs 10 tons).
 * Standard Internal Structure

It is the least bulky structure and does not take up any critical hit slots. It is also the least expensive and converting a 'Mech to it costs the 'Mechs maximum tonnage x 5,000 (on an Atlas, it would cost 500,000 ).

The Endo-Steel Internal Structure of a 'Mech weighs only 5% of its max. tonnage (i.e. on a 100 ton Atlas, it would only take up 5 tons), or half as much as Standard Internal Structure, but it requires 14 Critical Slots on Inner Sphere 'Mechs and 7 slots on Clan 'Mechs.
 * Endo-Steel Internal Structure

However, converting to Endo-Steel costs the 'Mechs max. tonnage x 10,000 (on an Atlas, it would cost 1,000,000.

Internal Structure Health
Depending on the 'Mechs tonnage, each of its locations has a certain amount of internal health, equal to 1/2 of the maximum amount of armor that can be mounted in that component. The one exception is the Head, which receives 18 internal hit points. (Note: The total health of the head component is somewhat disputed as some users claim to be able to "headshot" or "one-shot" 'Mechs with only a 35 point alpha strike. The maximum suggested here is 36, and could be less depending on the amount of armor allocated to the Head component.)

Number of equipable internal hit points with different 'Mech weights:

Note:
 * Each arm and leg has the given amount of internal hit points.
 * Each torso does not split internal hit points front/rear is they do for armor allocation.


 * Regarding Standard vs. Endo-Steel:
 * A 'Mechs maximum amount of internal health is independent of the type of internal structure equipped.
 * Different types of internal structure result in a different weight (tons) with equal health.
 * The trade-in for weight saving comes in the consumption of Critical Slots.

Taking Damage
When a battlemech's armour has been destroyed the battlemech starts to take damage to its internal structure, weapons systems and other equipment. When the internal structure of a battlemech's head, center torso or both legs are destroyed, the battlemech is destroyed. If an XL engine is fitted to the battlemech, the destruction of a side torso will also destroy the battlemech.

Savings
Compared to the weight saving of Armor, switching to an advanced internal structure provides a greater saving, i.e.:
 * Commando (25 t): Armor (Standard : Ferro Fibrous) 8.06 : 7.47 t vs. Structure (Standard : Endo Steel) 2.5 : 1.5 t = armor 0.59 t vs. structure 1 t
 * Cicada (40 t): Armor 12.56 : 11.65 t vs. structure 4 : 2 t = armor 0.91 t vs. structure 2 t
 * Hunchback or Centurion (50 t): Armor 15.57 : 14.44 t vs. structure 5 : 2.5 t = armor 1.13 t vs. structure 2.5 t
 * Cataphract (70 t): Armor 20.56 : 19.11 t vs. structure 7 : 3.5 t = armor 1.45 t vs. structure 3.5 t
 * Atlas (100 t): Armor 29.19 : 27.13 t vs. structure 10 : 5 t = armor 2.06 t vs. structure 5 t

Upgrading the Structure
To switch between Standard and Endo-Steel Internal Structure, use the Upgrades tab in the Mech Lab and choose structure.
 * Switching to Endo-Steel requires that you have enough money and Critical Spaces available on your 'Mech.
 * Switching to Standard Structure requires that you have enough money and tonnage available.