1. Faulty Reload/Weapon System
An ammo using weapon system suffers from having an inconvenient, overly complicated, or just poorly designed ammo feed system. Most of the time the weapon functions fine, but runs a minor chance of jamming or otherwise becoming inoperative. While clearing a jam is possible in the field, it takes the vehicle operator some time, from a few seconds to force a round to eject, to several minutes coaxing a missile through a feed tube without setting it off.
Weapon jamming can be an acquired flaw if a mech is operating in adverse conditions, especially in desert conditions where sand, or other contaminants can foul moving machine parts. Likewise, reconditioned and repaired weapons can suffer from this drawback. Many retrotech, salvaged, second line, mercenary, and otherwise non-top shelf level vehicles can suffer from this flaw.
2. Bad Reputation
Some war machines gain a bad reputation over time, and often this reputation is undeserved. For fill in the blank reason, the vehicle has a horrible reputation. Maybe the A model had a bad habit of exploding, or there was a plasma vent under the pilots seat, or the machine was famously used to execute blind school children. The machine is functional and fully sound, but no one wants to carry parts for it, no one wants to work on it, and no one wants to pilot it.
Bad Reputation is a social modifier, and the best pilots and crews are not going to operate these machines, unless there is nothing else for them to use. On a battlefield, these are likely to be the first machines targeted, least likely to receive support, and the most likely to be behind on their maintenance schedule.
3. Prone to Overheating
machines and heat don't typically get along. Heat generating components like reactors, energy weapons, capacitors, and the joints and actuators typically have cooling jackets, coolant systems and other mechanisms to help them dump waste heat. The mecha in question, one of these systems has a faulty or poorly designed coolant system. The specific system afflicted either generates more heat per use (weapons) or per turn (engine) or the non heat generating part (leg, hip, central rotator ring, etc) can be prone to seizing up from overheating and has to be broken loose by maintenance or an improvised field repair.
Machines that are prone to overheating are more taxing on their crews and pilots, and these operators fatigue much more quickly than other soldiers. A machine that has overheated will run the risk of having the overheating component fail due to safety systems (power plant, motor, energy weapon) or the component (joint, actuator, rotator ring, other moving part) will burn out its lubricant and seize.
4. Compact Crew Area
Few military vehicles are designed with the luxury and comfort of the pilot/crew in mind. Vehicles with the Compact Crew Area flaw have cockpits/cabins/crew areas that aren't just small, they are cramped. Moving around is difficult, and getting in an out of the vehicle can take some Houdini level contortionist skill.
The compact crew area is fatiguing to operators, and in the event of an accident, escaping the vehicle can be a problem, and in many instances, the lack of crew area often coincides with a lack of crew safety implements, leaving the vehicle in question likely a death trap for those unfortunate enough to operate it.
5. Poor Safety/Escape System
Almost all military vehicles have a way to bail out, and implements to ensure the safety and survival of the crew, from internal armoring, impact resistant systems, ejection seat, escape hatches, and so forth. The PSES flaw represents a vehicle with either grossly inadequate, excessively complicated or simply non-existent safety equipment.
Vehicles with this flaw almost always take their crews with them when they are destroyed in combat. As such, these vehicles can also suffer from the 'Bad Reputation' flaw, depending on how prevalent the issue is.
6. Poor Design
Poor design can lead to machines that are much more difficult to work on than they should be. This can be as simple as using completely different bolts and fittings from system to system to overly complicated arrangements and lay outs, such as requiring removing major components for minor repairs.
Military equipment can often be sourced from many different companies and suppliers, and use part with entirely different measurement standards, language barriers, or have gone through a large enough number of redesigns that it has become a mess of misplaced parts, poorly routed systems, and so forth. Logistic costs are increased, as are the amounts of time required for maintenance.
7. Poor Shielding/Electronics
Energy weapons, advanced and exotic power sources, strong radio transmitters, RADAR systems, and all sorts of other electronic gadgets make all sorts of electromagnetic noise. The majority of military vehicles are equipped with all sorts of things that muffle this noise, and protect sensitive components from it. That is, military vehicles other than the one in question. The machine suffers from feedback, and EM bleedover from one system or another, and this can range from annoying and inconvenient, to the problematic such as another system being knocked out by the offending system.
A common modification in mecha and wargaming is to add energy weapons to conventional machines. These machines weren't intended to carry high energy weapons, and firing these weapons subjects the vehicle in question to the EM backwash from the guns. This is also a common flaw for machines that have been kit-bashed or constructed from battlefield salvage.
8. Exhaust/Engine Weak Point
The engine/power core tends to be one of the best and most heavily armored components of most military vehicles, taking out the engine is an effective method of destroying an enemy vehicle. Unfortunately most engines have byproducts that need to be disposed off, such as heat, waste gases, radiation, etc and the vents for the engine can be a weak point. Most vehicles negate this by having armored vents, baffled exhaust systems, and so forth to prevent a good shot from going up the proverbial tail pipe into the engine. The vehicle with this flaw functionally has a location that can be targeted by infantry and smaller units to attack. Making a called shot with a suitable weapon automatically inflicts a critical hit on the engine. Equal sized and larger vehicles cannot exploit this weakness.
Mecha, armor, warships, etc all have a smaller class of enemies that are trained to engage and destroy them, from anti-mech and anti-armor trained infantry, to fighters armed with anti-ship missiles, and so forth. So long as the attacking unit is smaller than the unit it is attacking, it can maked a Called Shot to hit the weak point, and if successful, this will either cripple the engine, or completely destroy it.
9. Exposed Weapon
The exposed weapon is rather self-explanatory, it is not protected by the armor sheath of the vehicle carrying it, and it has no integral armor protection of it's own. The weapon can be destroyed or disabled by a called shot against it. If the hit it successful, damage is applied to the exposed weapon, but not against the vehicle mounting it. This is common for shoulder mounted pod systems, hand held mecha style rifles, and other bolt on, often one shot weaponry. On non-mecha vehicles this can represent equipment mounted outside of the vehicle such as roof mounted rocket launchers, laser systems, etc that are not armored. Machine guns mounted on top of a vehicle often have a ballistic shield or guard in front of them, and do not count as exposed.
The weapon system can be the subject of a Called Shot, and if the shot connects, rather than inflicting damage, the exposed weapon is instead either disabled or destroyed. If there is a critical success on the called shot, any ammo in the weapon detonates, and inflicts its base damage on the unit, such as a cannon exploding in a mech's hands, or the roof mounted rocket launcher blowing the top off of a light armored vehicle.
10. Fragile Fuel Tank/Power Cell
Nothing ruins a vehicle's day quite like having it's fuel supply blow out in a gout of flame. The vehicle has inadequate shielding, poor positioning, or otherwise has a power cell/fuel tank that it easily hit by weapons and depending on what sort of fuel the vehicle uses, can range from a blast of burning fuel, sprays of caustic battery acid, or a pressure explosion.
The vehicle has it's fuel tank/cell as a critical hit location and can be targeted by a called shot. Common sense comes into play, and even the worst designed tank is not going to have a gas tank in the front, so hitting this weak point typically involves flanking maneuvers, or units trained in anti-vehicle warfare.
11. 4 Gallons to the Mile
Military hardware is seldom designed to be economical and thrifty, the big machines require large amounts of power to move, and require extensive amounts of logistical support. But there is a certain expectation of range and duration that a machine in the field is expected to have. The Power Hog doesn't come close to this expectation, and falls far far below it. The power hog requires higher than average power system maintenance, and its reactor has to be conditioned much more frequently. In mecha, the most common power hogs are the machines that rely heavily on energy based weapons, and ballistic weapons like rail guns that do use electricity.
At 80 tons and mounting nothing but lasers and large particle cannons, the Awesome class assault mech is a premiere power hog. It's power plant is compact and while it can handle the load of moving the machine and keeping the guns hot, it does so by running in a power band far higher than most mecha reactors.
12. It's Like Strapping Yourself to a Bucking Bronco
One of the innate advantages of the mech is it's innate natural ability to be piloted. It looks humanoid, it feels humanoid, and it moves humanoid. Most mech training isn't so much walking and moving, its getting used to being a giant and not causing collateral damage by incident or accident. Unlike these common machines, the hard to pilot mech has glitches or design features that make it's control difficult or non-intuitive. This can range from a very specific aspect of it's design, such as non-humanoid mecha like quads or four legged mecha, to poor design or questionable functionality, such as the the hunched and often top heavy walker/pod type mecha.
The Scorpion medium mech isn't popular with pilots. It is ugly, it's squat, and it's hard to control. The mech's legs, all four of them, stick out to the side like a lizard's. This makes the mech a very stable firing platform, but it's gait is unnatural, and in the hands of an unskilled pilot, often jarring and painful.
13. Walking War Treaty Violation
War is a fickle thing, what is perfectly acceptable in one war is suddenly against the rules of war the next time things heat up. Unlike mustard gas, notched bayonets, and bombing entire cites to ash with incendiaries, the mech in question is built around a method of war, or its main weapons have been deemed unforgivable in the theatre of war. Alternately, the machine could have other features that are now functionally illegal.
Real World Example: New Zealand has a no-nuclear rule, so ships that are powered by nuclear and atomic power sources cannot legally enter Kiwi waters. In a sci-fi setting, the mech is built around a controversial weapon or power core, such as a tiberium reactor, high energy weapons that puke waste radiation, or atomic, biological, or chemical weapons.
14. Inaccurate Weapon
There are weapons that for whatever reason are inaccurate, it can be a function where the weapon doesn't have to be accurate, such as missiles designed to carry atomic warheads, or short range weapons, or by design are just not accurate. In mecha this can be an oversight of the weapon, or it's placement in the mech. A gun buried in a mech torso is going to be limited in it's functional accuracy compared to something mounted in the arm. Cheaply made, arcanotech, exotic, and other weapons can also suffer from this flaw. Cheap ammo in rail guns deform when fired, lightning lances are not accurate, flamethrowers are not precision weapons.
15. Large Size
Military hardware is generally designed to be compact to make it harder to hit. Sometimes this isn't possible, or for whatever reason the mecha in question is large, has prominent features and it otherwise easy to hit. This is and should be a common flaw for assault mecha and other superheavy vehicles. Most vehicles with this flaw tend to be very well armored.
16. No Cooling Jacket
A common flaw of energy weapons and rapid fire weapons is the potential for the weapon to overheat. Most weapons have cooling jackets, or some other method of dumping this waste heat. In the Cosmic Era, there are dimension heatsinks, laser heat dissipators, and conventional radiators. A mecha with this flaw has a weapon that isn't connected to this cooling system, and has the potential to overheat and either lock up or explode. This is a common flaw for non-mounted weapons such as mecha rifles and other carried weapons.
17. No Ejection System
Space in mecha is limited, and to save weight, space, and sometimes even cost, the mech doesn't have any sort of ejection system other than opening the hatch and jumping out. This generally makes the mech a walking coffin, and most pilots will intensely dislike riding in such machines.
Light and scout mecha, and almost all civilian and industrial mecha are not going to have ejection systems. Some cheap made mecha, and assault mecha lack ejection systems as anything powerful enough to destroy these machines isn't going to leave the pilot alive.
18. Non-Standard Parts
Every nation is going to have it's standards of manufacture and source and supply chains. The mecha or vehicle in question is outside that supply chain, being a foreign import, or an amalgam of equipment from different sources cobbled together to function. The effect is that logistic costs for supporting the machine are 25% higher than normal due to the non-standard tools and parts.
A common flaw of cars in the late 80s and early 90s was the confluence of American and Japanese car manufacturers, combining resources and technology. The resultant cars had both metric and imperial parts and required full sets of both size tools to work on.
19. Limited Mobility
One of the biggest advantages of mecha over other ground vehicles is mobility. A mech with limited mobility is a liability, and typically represents either a machine that is ponderously slow, such as artillery vehicles, poorly suited to a specific environment, like a land supremacy mech in the water, or has a strange design quirk such as having three legs. Modified civilian and commercial mecha often have this flaw as they are seldom built fot r speed and agility.
A forklift is a slower ponderous vehicle.
20. Grandpa's Guitars! (obsolete)
For being cutting machines, in most settings mecha have been in use for years. Over those years there are going to have been many small upgrades and new technologies integrated into the mech. The obsolete mech is a throwback to an earlier era of armored warfare and its systems are out of date, the chassis is showing fatigue, and parts are getting scarce. While the machine can have a good reputation, it is still functionally a dated machine, and is treated accordingly. Logistics are 10% more expensive, and pilots are unhappy when assigned to the machine.
The B-52 Stratofortress is more than 60 years old, and the only parts available for the aircraft are being cannibalized off othe stockpile of retired aircraft. While the systems and electronics are being constantly upgraded, the airframe and the engines are still the same 60 year old pieces of equipment, and while aircraft are faster, more efficient, and more stealthy, the Stratofortress is a relic of an era of the Bigger, the Better.
21. But it Sold Well on Paper
There are a variety of machines that for a variety of reasons, just don't perform well. The poor performance of the machine has been noted and while there are steps being taken to address the flaws, there are just so many of the machines in service that replacing them is just not possible at the current time. Maintenance costs are increased 10%, and deprived of logistic support the machines suffer a small increase in their chance of breaking down and having mechanical failures.
The Humvee, or Hummer is a mechanically complicated machine that performs poorly in the roles assigned to it. The excess complication makes it prone to breaking down, and the vehicle is being used for roles it was never intended for.
22. Poor Sealing
The Vehicle in question has poor performance in hostile environments and is prone to springing leaks. This can be a marine/litoral/submarine vehicle with water leaks, or a high altitude/space vehicle that cannot hold atmosphere. While the majority of the vehicles with this flaw are safe, there are enough that have these slow leaks, or a preference for failing seals that the machine has a reputation for it.
Marine vehicles can lose mobility, have system failures due to flooding or just sink. Space vehicles can have compromised life support issues and overheating/freezing issues with loss of atmosphere in a component.
23. Poor Communications
For a variety of reasons, the vehicle doesn't communicate well, and it is easy for units to drop out of LAN combat networks, lose radio comm, etc. Some common reasons include poor antenna design, faulty radio system components, a habit of a communication line getting sheared by moving components, etc.
Mech pilots with this unit know to carry a back up mode of communication or know mech sign language. In combat, a unit cut off from information is going to be less effective and more vulnerable. On the plus side, units with bad comm systems are less likely to be hacked or taken down by electronics warfare.
24. Poor Computer
Mecha are controlled predominantly by Limited artificial intelligences, LAI computers. These machines control the movement of the vehicle, aiming the weapons, and are the limbic and sub-consciousness of the machine where the pilot is the will and ego. Not all LAIs are created equal, and the mech in question happens to have one of those less than stellar LAI unit. The LAI could have a poor response time, of move the machine with a constant lurching gait, or have the artificial personality of the Microsoft paperclip.
A -1 to -3 penalty to certain tasks would work, or an irritating personality profile. A determined LAI that talks to itself like Rain Man, or a constantly panicky LAI that seems on the verge of a nervous breakdown, etc.
25. Poor Targeting
Sometimes shooting this is hard, and typically fast moving distant objects are harder to hit than things up close. A variation on the poor computer flaw, the poor targeting flaw is a targeting computer/system that isn't very good for hitting a certain type of target. In a mech, the targeting system will lock onto a target, and then sort out which direction it is moving, how fast it is moving, correlate that data to the velocity of the weapon system, and calculate out the most likely trajectory to get the projectile/beam to meet the target. This can be as simple as the machine trying to lead a target with an energy weapon (always shooting well in front of a target) or always assigning a movement factor even to stationary objects (leading a vehicle that is stationary) or just being balls to hit anything but the broadside of a barn.
This should be a rare flaw, and if encountered should be on kit-bashed mecha, trainer machines, hard used machines that are in desperate need of overhauling and system debugging.
26. Poor Workmanship
Like the Yugo, some mechs and vehicles are just made piss poor. While the big stuff works (until it doesn't) the small parts rattle loose, switches and buttons are quirky in their function, and a good deal of percussive maintenance and verbal abuse from the pilot is required to keep the machine running.
Poor Workmanship flaw grants the machine an automatic critical hit, but rather than be destroyed, the component indicated is simply not working until it is examined, and given maintenance. This can be actuators and joints seizing up, electronic systems needing to be power cycled, weapons glitches, or even the entire LAI or power core needing to be power cycled. Nothing like striding across a battlefield with a Check Engine light blinking on the console.
A common theme in mecha design are mechs with gigantic cannons mounted asymmetrically on the chassis. These objects throw the center of mass of a mech off, as do having giant missile pods and other weapons mounted high on the torso. While walking this is no issue, but when running, firing on the move, and other piloting dexterity skills, these machines require much more deliberate skill to keep upright and not on their backs or flat on their faces.
A good standard is a -2 to piloting rolls when handling something like this (For those in know: I'm looking at the Hollander, the Hunchback, and the Longbow). For personal experience, pick up a 40 lb feed sack and go running with it.
28. Known Weak Point
Video Game bosses have flashing weak points, but mecha don't. The mech with the Known Weak Point might as well have a neon sign or flashing lights around it's weak point because everyone knows where it is, and everyone goes right for it. This is a common flaw for older machines that have been in use for a long time. When it was new, and hadn't seen heavy combat, that achilles heel wasn't known.
Called shots usually get a pretty high difficulty modifier, but against the Known Weak Point, the difficulty is lower, and if the called shot is made, it is an automatic critical hit against the known weak spot, no rolling to see what might be hit. Thermal exhausts guarantee an engine hit, weak points in armor are a certain thing for knocking out a limb, or blowing up a weapon.
29. Poor Armor
Not all armor is created the same. Sometimes the composite sandwiching has a habit of separating, or the metal used has stress and fatigue issues and just can't take a beating like similar armor. This flaw can come from either dated machines, experimental armor that failed, or just crappy quality armor.
Reduce the damage rating of the armor by a step (if using a defensive rating) or certain types of weapons do more damage, or all weapons do 1 point of extra damage (if using armor dot method). Maintenance on the armor is likewise increased 10% in cost.
It is easy for a combat vehicle to end up overweight. Supplemental armor can be added, and weapons are upgraded, and there are hardpoints and backpack systems and eventually the chassis designed to hold 40 tons of mech and 15 tons of equipment is straining under 10 to 50% more weight than it was intended to bear. Such machines suffer from chassis failure, wearing out components much more quickly and requiring more extensive maintenance to keep them up and running, Top speeds are likewise reduced by the excess weight of the machine.
Overweight mechs have their speed reduced 25%, and take double damage from critical hits against superstructure and chassis elements.