I've long been intrigued by battledroids infantry - squad-sized units that carried an MG or SRM-2. They received a +2 TH mod when attacked but died in a single hit. You could also stack ten of them in a hex :))
I've updated these rules for the modern game with a few "improvements" (they may not actually be improvements - I'm not very smart). I've largely replaced the current infantry rules here and force them to use Battle Armor scaled weapons to be a meaningful anti-armor asset. Also to reduce the equipment list.
Disclaimer: This exercise assumes that small arms and infantry support weapons do not damage mechs in meaningful ways apart from total luck. If you have a problem with that premise, I have good news - the official rules support your position. I am here to present an alternate reality.
General Rules
* Infantry units are organized and deployed by squad
* Each squad carries a single weapon from the Battle Armor equipment list (weight limited by unit type)
* All infantry types have a 360 degree firing arc
* Motorized infantry move like vehicles and must pay for facing changes. Motorized infantry does not skid or sideslip
* There are three varieties of infantry - Foot, Jump, and Motorized (subdivided as Tracked, Wheeled, Hover)
* TW Mechanized infantry doesn't exist - that can be represented by using extant support or combat vehicles.
* A single hit eliminates a squad - the men aren't necessarily killed, but a successful attack destroys the squad weapon capable of doing damage.
* All units are restricted to the terrain inherent to their movement type.
* All units receive a +1 TH mod as with Battle Armor, plus any bonuses received through movement
* Units may select an anti-personnel machine gun with a range of 1/2/3 that provides a -2 TH mod against other infantry units. It will not damage non-infantry.
Foot Infantry
Movement: 1mp
Squad weapon maximum weight: 75kg
Common Options: SRM-1, LRM-1, Light Machine Gun, Light TAG
Jump Infantry
Movement: 3mp
Squad weapon maximum weight: 50kg
Common Options: Firedrake Needler, Light TAG, Mine Dispenser
Motorized (Wheeled)
6/9 movement (cannot fire if using flanking movement)
Squad weapon maximum weight: 250kg
Common Options: LRM-4, SRM-4, Support PPC, Compact NARC, Light TAG
Motorized (Tracked)
5/8 movement (cannot fire if using flanking movement)
Squad weapon maximum weight: 400kg
Common Options: SRM-6, LRM-5, King David, Flamer
Motorized (Hover)
8/12 movement (cannot fire if using flanking movement)
Squad weapon maximum weight: 150kg
Common Options: SRM-2, LRM-2, Compact NARC, Light TAG
1-50kg weapons (Foot, Jump, Hover, Wheeled, Tracked)
Firedrake Needler
Light TAG
Mine Dispensor
Rocket Launcher 1
Rocket Launcher 2
51-75kg weapons (Foot, Hover, Wheeled, Tracked)
Grenade Launcher (Micro)
Machine Gun (Light)
MRM-1
LRM-1
Rocket Launcher 3
SRM-1
76-150kg weapons (Hover, Wheeled, Tracked)
Compact NARC
ECM (Single Hex)
Flamer
Gauss Rifle [David]
Gauss Rifle [Grand Mauler / Tsunami]
Grenade Launcher (Heavy)
LRM-2
Machine Gun
Machine Gun (Heavy)
MRM-2
Rocket Launcher 4
Rocket Launcher 5
SRM-2
151-250kg weapons (Wheeled, Tracked)
Active Probe (Light)
Angel ECM
BA C3
Magshot
LRM-3
LRM-4
MRM-3
MRM-4
Recoiless Rifle (Light)
Recoiless Rifle (Medium)
Small Laser
SRM-3
SRM-4
Support PPC
251-400kg weapons (Tracked)
ER Small Laser
Small Pulse Laser
Gauss Rifle [King David]
Heavy Flamer
LRM-5
Mortar (Heavy)
MRM-5
Plasma Rifle (Man-Portable)
Recoiless Rifle (Heavy)
SRM-5
SRM-6