It is an unfortunate but easily demonstrated fact that consoles in Star Trek Online often perform in ways that bear only a passing resemblance to what they claim to do in their descriptive tool-tips.
I will be discussing three different categories of consoles in this post: energy weapon damage boosting consoles, projectile weapon damage boosting consoles, and RCS accelerators.
Long story short, for those who don't want to read it all:
All three of these console types will give you less of a boost than what you would expect from their listed stats, and it has absolutely nothing to do with diminishing returns.
Energy Weapon consoles
Energy weapon damage consoles state in their description that they boost your damage by a certain percentage. This, I'm sorry to say, is simply false.
A +26% damage console will not increase your weapon damage by 26%. Not 26% of your modified value, not 26% of your weapon's base damage, not 26% of any number that is any way relevant to you or your ship.
What it will increase your damage by is 26 points, when your weapon is set to 50 power.
This holds true for all lower power consoles as well. The listed "percentage" is actually the flat numerical boost to damage that that console will give you at weapon power 50.
Like the base damage of the weapon, this is then modified by adjustments to your weapon power. At 100 power, energy weapons do double the damage of their base value. Accordingly, at 100 power, a +26% console is worth approximately 52 extra damage. There may be a variance of 1, due to behind-the-scenes rounding of numbers.
At 125 power, the power cap, energy weapons and their consoles do 150% of their listed values. So the greatest increase in damage that you can ever gain from a single energy damage console is approximately 65 damage,
Note that as the math behind these consoles never checks the base damage of your weapon, that the increase will be the same for all weapons of the correct damage type, regardless of their base damage. A Mk X, Mk XI, and Mk XII weapon will all have their damage increased by the same amount.
There are no diminishing returns on these consoles. A second console of equal value will increase your damage by the exact same amount as the first (allowing for rounding, which may lead to single point discrepancies). The same holds true for third and fourth consoles.
Projectile Weapon consoles
While discussing the above findings in Earth Spacedock, someone asked about projectile weapon consoles. As power levels don't play a role in their damage, they clearly cannot be using the same mechanism as the energy weapon consoles. Another player said they'd check, and returned to say that projectile weapon consoles worked as they claim to, boosting his damage by the appropriate percentage.
I opted to double check on my own vessel, having recently looted a rare Mk XI quantum torpedo console.
Unfortunately, I found that it did not increase my quantum torpedo damage by 26% of the base damage of my launchers. Well short of it, in fact.
So I decided to do some research. Not wanting to blow large chunks of EC on consoles I didn't need, I decided to work with the following items to test my math: a Mk VII common photon torpedo console (+15%), a Mk XI common photon torpedo launcher, and a Mk I Photon torpedo launcher. On a whim, while buying the Mk I launcher on the exchange, I also grabbed for 1 EC a Standard Issue photon torpedo launcher, the very base equipment your first ship comes with.
I installed the Mk I and Mk XI launchers on my ship, and then installed the console to see how much it modified the values by.
A Mk XI photon torpedo launcher has a base damage of 2842. A 15% increase would be an additional 426.3 damage. The Mk XI launcher instead gained 203 damage.
A Mk I photon torpedo launcher has a base damage of 1462. A 15% increase would be an additional 219.3 damage. The Mk I launcher instead gained.... 203 damage. The same amount as a Mk XI launcher.
Clearly the console is not modifying either weapon by 15% of their base damage value. They both gain the same amount, and that amount is less than what the math says a Mk I launcher would gain.
On a whim, I looked at the Standard Issue launcher (which, I should note, was not installed on my ship at any point). It has a base damage of 1352. A 15% increase would be an additional.... 202.8 damage.
So yes, projectile damage boosting consoles apparently are indeed percentage based, unlike their energy weapon counterparts. However, they do not boost your damage by a percentage of your current weapon's base damage. Instead, they boost it by a percentage of the absolute base value for that category of weapon, a common Standard Issue (lower than Mk I) version. Note that such launchers are not available in game, other than the photon torpedo launcher.
I have not yet checked using multiple copies of the consoles, to see if that leads to diminishing returns. My prediction (which I will check later) is that each +15% console will increase photon torpedo damage by another 202.8 damage.
I will also, just to cover my bases, check a couple of other damage types and their consoles, to make sure this isn't an oddity that only affects photon torpedo launchers.
Currently very popular due to the release of the slow-turning Odyssey and BortaS ships. I'll reiterate my earlier findings to establish just how bad these consoles are on those ships. I should note that my tests predate Season 5, and it's possible the set-up has changed since then. However, there have been no patch notes indicating a change. To the best of my understanding, all turn rate increases from skills work from your base value, and would not affect the consoles in any way.
RCS Accelerators claim to increase your turn rate by a percentage value. The best in the game grant +34%.
They do actually grant that much of a boost, but not on your actual or base turn rate.
Instead, the formula for how much you gain is as follows: (Base Turn Rate - 3) * RCS Accelerator boost = Actual Gain in turn rate in degrees per second.
So the actual benefit is always lower than if it was a straight percentage based boost from your base turn rate. Even worse, the lower your base turn rate is to begin with, the greater the impact that the -3 modifier has on the final result.
The difference, for instance, on a Bird of Prey`s 23 base turn rate is as follows:
Straight percentage boost (34% console): 7.82 deg/sec
Actual boost: 6.8 deg/sec
Galaxy class base turn rate of 6
Straight percentage boost (34% console): 2.04 deg/sec
Actual boost: 1.02 deg/sec
Note, that as all player-facing numbers are rounded, some of my math will be off slightly due to behind-the-scenes rounding. However, I'm sure you'll find that my results are quite close to what you actually gain, unless there's been a significant and unmentioned change to these consoles.
The Odyssey class, according to dev posts about final stats, has a base turn rate of 5.5
Straight percentage boost (34% console): 1.87 deg/sec
Actual boost: 0.85 deg/sec
Now, I'm sure plenty of you would say that you can feel the difference in turn rate that such a console makes. Perhaps you're much more sensitive to minute changes in turn rate than I am, but I'm pretty sure a change of less than a degree per second is at the very limits of my ability to actually notice at all. It's certainly a small enough boost that I feel it's not worth spending one of my console slots on, when there are consoles which make far more significant changes to my ship available (though I have begun to doubt that any of the consoles does what it claims to, and will need to check some of my assumptions).
As far as stacking and diminishing returns go, there are no diminishing returns on RCS Accelerators. Allowing for differences due to rounding, you'll find that each RCS Accelerator of equal value adds the same amount of boost as the last.
Feel free to check any and all of my findings, and let my know if my results are off.
I'd like to see a dev comment on this and review the results that you put forth. Not because I think that you're wrong, but to see how they respond since they claimed that the damage consoles did work on percentages and diminishing returns.
Most consoles (the ones that boost skills) don't work the way you say. Consoles all to the skill bonus that get get. At rank 9 of a skill get have 99 skill bonus. If the full bonus value is used for an ability the boost you get is X * (1 + ( <skill bonus>/100 ) ). For for skill bonus of 99 it's X * 1.99. Almost double the base value. Consoles are just added onto the skill bonus. So if you have 2x +25% consoles you are adding +50 to your skills strength. So X * ( 1+ ( 99 + 50 )/100) = X * 2.49.
Weapons are a bit more complicated as they are a two other factors in the math according to Al Rivera on the Prioitu 1 Interview. First is he "Strength" of the weapon depending on the Mk (5 or 10). And the "Strength" of your ship depends on it's Tier. "Strength" is a hidden value of the weapons and ships. I assume it's reflected in the pop-up info of the weapons. The example Al used are Mk 10 Weapons have a "Stregnth" of 1. And Tier 5 ships have a "Strength" of 1. Skill Bonus and Consoles totals are other factors the ship and weapon strength values. So: base weapon damage * ( 1 + ( <weapon strength> + <ship strength> + <skill bonus> + <consoles total> ) / 100 ). Weapon power for Energy weapons is a straight multiplier to the adjusted damage based on eh scale you described.