Armor

Armor is usually the main line of defence of your robot, equal to hitpoints in most other games. Once it hits zero - you explode and lose your robot.

However, there are a lot of methods to try and keep yourself in one piece. One we won't cover here is using a Shield

Extensions
Extensions that affect armor tanking

Armor repairer
Armor repairers are active modules that repair your armor at the start of their cycle. Frequently used on most bots, in both PVE and PVP

Small
Small repairers are characterized by their relatively high efficiency (amount they repair per Accumulator Point) but low repair speed. Usually used on assault bots, but can be used on mechs as a supplementary repair method due to their low fitting requirements and low weight.

Medium
Medium repairers, conversely, repairs much more per cycle of operation but consumes much more energy as well, at a ratio considerably lower than small repairers.

Large
Large repairers are capable to repair around twice the medium's amount, but they're extremely demanding in terms of fitting. Only Destroyers can effectively use them; also there isn't any Flawed (T0) nor Niani (T3-) variants, but instead the Standard Prototype (T1P) is introduced.

Armor repairer tunings
Repair tuning boost the efficiency and repair speed of any equipped repairer, both normal and remote variations. Highly popular on Nuimqol bots and logistics.

Remote Armor repairer
Remote repairers share most of the characteristics with regular repairers but are a little less efficient and can only be used on other bots. There is no way to use them on yourself.

Armor Plates
Plates increase the armor pool of your robot by a flat value and provide defence against demobilization at the expense of having a fairly high weight. Any amount of plates can be fitted to a robot (assuming you have enough Fitting), and demobilization resistance bonus stacks up linearly.

LWF
Lightweight frames are nearly the exact opposite of plates, they increase the speed of your robot considerably, but reduce armor and make you more vulnerable to demobilization. Only one LWF can be fitted at any time, making T4 LWF usually the best choice if you can afford it.

ERP
ERP's are the Energy Reclaiming Plates; they doesn't give additional hitpoints nor resistance points; yet it has a curious property - it can reclaim a certain percent of incoming damage type into accumulator energy (in AP). Normally there are 3 types of ERP's; each of them are geared towards one damage type (Thermal, Kinetic, Seismic).

For their designed damage type; they're able to process 70% of the incoming damage into AP, while for other types (excluding Chemical), only 15%, making them useful only in niche situations.

There isn't any chemical-oriented ERP, but all ERP's have a fixed 30% reclaimation of the chemical damage.

Armor hardeners
Armor hardeners (also referred to as "resistance plates" sometimes) increase the resistance of your Armor against incoming damage by certain points. Dedicated plates (vs. Kinetic, Thermal, Seismic & Chemical) can boost your resistance by small percentage passively, or they can be activated to give a big percentage, but in turn it'll use Accumulator (like any activated module) for operation.

There are also the Universal Plates, which boosts resistance for all damage types passively, but in turn it's a purely passive module.

Armor NEXUS
Armor NEXUS boosts all squad members armor hitpoints for certain percent (which varies, depending on NEXUS module tier and revelant skill level) in area of at least 100m (can be raised with revelant skill) from the NEXUS operator (assuming that no other Armor NEXUS, or more than 3 NEXUSes are active in the operating area).

Keep in mind that added hitpoints are "damaged", so you have to use repairer to use the increased hitpoints.