Balancing the Thruster Numbers

Hi Guys,

Just been taking a look at the stock value for thruster performance in order to update my own Prometheus XL mod and things are looking more than a little confused in ol' CubeBlocks! There doesn't seem to be any sort of consistency between any of the performance aspects of the thrusters; thrust, power requirements, mass and size.

At the moment it looks something like the below...



Let's start with the thrust provided by all 4. The small engines are nicely in line with each other with a mutual 6000 N per block each, so no problems there. The large thrusters however have 144,000 N for the small and 150,000 N for the large... which not only doesn't match but it actually gives the large thruster (which is deeper and can be stacked on an extra axis) a superior performance. Really thrusters should either be directly in line with each other, or suffer from penalties as they get deeper on the third axis, not gains (otherwise larger ships can in theory outperform smaller ships with equal percentages of their volume dedicated to propulsion).

Power wise again the small thrusters are more or less right on; the difference is in the small decimals, so no problem there I think. The large thrusters however are again confusing but possibly correct. The small is a lot more efficient at 1.68/block compared to 1.4/block. It's possible this is intentional as it does make sense for depth penalties (though it is really quite a harsh one for going from 2 deep to 4 deep!)

I'd be very, very interested in some feedback from the devs here - do you have a current calculation you use to determine stock performance? If so, can we see it please so that we can balance our mods to correctly match your intended balancing?

If these are just rough numbers they have been given, can I suggest the following changes:

Thrust set to 150,000 per block. Power consumption set to 1,500 N per block:

Large Grid Large Thruster: Thrust remains 3,600,000. Power usage increased by 2,400 N (2.4) for a total of 36.0.
Large Grid Small Thruster: Thrust increased by 12,000 for a total of 300,000 N. Power usage reduced by 360 (0.36) for a total of (3).

Again, while it seems odd the large thruster has better power performance, if this is intentional, letting us know the maths would be a huge help so we can keep our own work in-line.

Secondly, the power also seems to be all over the place. In a small grid, the large reactor is slightly more efficient but on the large grid it suffer from a BIG penalty (seems like far too much!) I have no opinion on whether smalls or larges should be more efficient, I can see arguments for both, but really they should be inline between the grids and maybe not quite as harsh!

At the moment, on the small grid, the large is 10% more efficient so...

Suggested Changes: Large Grid, Large Reactor = 445.5 instead of 300. (This gives a power/block of 16.5; 10% more efficient than the small).

This may also go a long way to giving people who's ships now don't come anywhere close to working a chance

 

when you say 'block' are you muliplying the large block dimensions by 5 to get the same measure of volume as the small grid? also, try working the numbers for only the block portion of the thruster. excluding the nozzle.

 

For a better comparison, you need to add mass and number of thruster components to your spreadsheet. Those numbers are more important than "per block" in my engineering experience. You could also use thrust/power, thrust/mass, and thrust/thruster component as your comparisons.

Personally I think the power consumption should be better on the large thrusters, but not in the proportion they currently are; maybe 20% better instead of 80% better. Thrust per mass feels like it scales incorrectly though; thrust per mass in physical engines generally goes up with size*, whereas currently thrust/mass is going down. Thrust per thruster component, I think should be constant - so large ship thrusters require far too many thruster components for their thrust output compared to small ships.

*This is because the components that make an engine are shells, not solid volumes. Thrust generally also goes with nozzle area. But there are some components that don't need to get bigger as you make the engine bigger, so those masses don't scale with size^2. When an engine gets too big though, parts do have to get thicker to handle the size, so "big enough" thruster-type engines do end up starting to weigh more. So I guess if the claim is that the large ship thrusters are already beyond this point, that would make sense.

** Related random fact: Thrust scales with the area of a nozzle, not the volume of the engine. So the important factor for engines should be size^2, not size^3. All else equal, I would expect large thrusters to have 4 times the thrust of small thrusters (not ~12) and large ship thrusters to have 25 times the thrust of small ship thrusters. This latter is pretty close - 24 times for the small thrusters and 25 times exactly for the large thrusters. But the thruster component count is off.

 

i have no like button here...? @McTraveller, 'like'
agreed, a pump is a pump, and most of the thrust comes down to the geometry of the thrust nozzle, but if thats the case, why are the large thruster bases so much more massive? thats why i suggested balancing by base volume. while im very interested in a component cost rebalanced, the issue at the moment is what thrust (and at what energy efficiency) do the thrusters now run at when compared to each other. for example, is there a benefit to using a large thruster over six small thrusters?

 

Dunno... but it does seem kind of arbitrary to me. I can't think of any reason why the base of the large thrusters would need to be 3x2 instead of 2x2. Someone with more creativity than me could probably come up with a plausible explanation.

 

i believe its a matter of one rule for reality, another for keen

 

For centerline symmetry on odd-width ships?

 

you are probably right. i propose a 3x3x6 large thruster with 9x the thrust of a small thruster.

 

@Tristavius

Can you modify your spreadsheet to represent thrust per volume? It would also be nice to plot thrust per mass and thrust per thruster component.

 

Interesting to see the other feedback; while I feel my original points still stands, you've all added a couple of important extras to the equation which need to be considered.

Why 'Per Block' as the primary factor? Quite simply, for me (and a lot of other builders I know), the size of something is probably the single largest factor determining it's balance compared to a part of the same type. This is of course a product of the creative crowd and as quite correctly raised, material costs are a huge factor for the survival lot. Having never so much as built an interior plate in 1300+ hours, I am most definitely not the person to provide input on such things but needless to say it should be looked at.

Thrust per mass (basically your classic TWR) would be the logical balance point in a lot of space games. In KSP for example, being as almost everything barring a small payload tends to be engines or fuel, there is nothing more important. In SE however, the tech has really advanced to a point where engines make up a relatively small mass on most ships (especially compared to the hull itself) and fuel, probably the largest limiting factor in real world space flight, has become an almost non-issue. While it is something that can be balanced, I don't think it's something we need to think too much about really. As mass is determined by components, fixing one will fix the other.

What I don't agree with though is looking at small grids and large grids as comparatives to each other. While in the real world there isn't that same magical grid distinction, for reasons of game play I think we need to make it here. To keep small ships actually being useful, they have to focus on the one thing they do better... speed and maneuverability. While the changes to the large grid feel kind of okay at the moment (finding a couple of extra blocks to become reactors isn't too hard), small ships feel very underwhelming now; I don't know about you guys but for me, every single block on a small ship already served a specific purpose... if there could have been another reactor, there would have been already. The end result is that suddenly my fighters have gone from 10x faster to maybe only 2x faster... feels a little wrong.

In the below post, we were discussing my TVSI-Tech Prometheus XL thruster, and how I chose to balance the increase on the 3rd axis to ensure that larger ships would always be a little slower than smaller ones, even as engines got 'deeper'. What's listed here no longer works under the new system; consider this a historical discussion but still relevant to what's being discussed.

https://forums.keenswh.com/threads/tristavian-shipyard-inc.6997264page-$1.html#post-1286807957

My own belief has always been that we need a full set of gradually 'deeper' engines but that as they get deeper, there should be small performance penalties on thrust provided and on power consumption (or at very least just on the power) to ensure different sized ships still 'feel' different.

Exactly! Trust me, from a modding perspective and the feedback you get, the very best thing you can ever do with a part is give it one odd and one even side. A thruster, being as it's third axis is dictated by needing to point in a certain direction really only has 2 axis to consider, so having 2x3 makes perfect sense to allow both odd and even width placement. Of course, a larger variety of similar sized thrusters would solve this problem as well... having a choice would allow for more configurations and a relaxing of this rule.

3x3x6 = 54. 1x1x2 = 2. The engine you propose is 27x bigger than a small thruster. Assuming the component and thus mass also follow the same 27x bigger then the stock balance would be 7,776,000 N rather than the proposed 2,592,000 N. I'm all for 'depth penalties' but that seems a little harsh.

This is an awkward one, and one I though about often for a while. In the end I came to the conclusion that the nozle probably needs to count - it does take up space and plenty of players indent them to some degree to provide protection, thus while they are arguably 'external', too maybe people use them 'internally' for them not to be considered. It's true though that from a mass point of view, the nozzle blocks maybe need to be considered as lighter. Also, quite a lot on the mod front don't have the KSWH style nozzle and for me, a big point of all this, is to finally have a Keen agreed standard for engine balancing; something that's caused more than a bit of debate in the modding community in the past.

As requested, I'll put together ALL the facts including mass, component costs and so on as well as some proposals on balancing the whole lot out.

 

Id like to point out, that we live in a 3d space and the thruster base is in fact 3x2x2, not merely 3x2.
Still, why is the large thruster 1/3 bigger proportionally compared to small thruster?

 

Doesn't your table pretty much prove that Keen has not actually agreed on a standard for engine balancing?

The thruster itself is also only "half" the balancing problem. The other is the capability of the power source to run them The latest "balance" patch has actually made the power sources less balanced.

What about making the nozzle a separate module? And you can choose a nozzle profile, and thus thruster volume at a cost of performance? A very flat thruster = lower thrust but easier to inset into the hull. A huge nozzle = best performance but sticks out like a sore thumb.

 

I've put together the following suggested values for the Large thrusters (both present and future) which would, in my opinion, offer a balanced set of figures. It keeps the current settings much the same (while getting rid of some inconsistencies) and puts in place guidelines for imposing thrust/power penalties as thrusters get deeper on that all important 3rd X axis (how large it is on the other two is actually irrelevant penalty wise). I won't re-iterate the argument for doing so, it's been covered in plenty of places.

I'm going to list it in Thrust (N) per block and Power Usage (MW) per block; calculating values for additional sizes is then as simple as looking up the depth values then multiplying by the number of blocks.



This would give the current stock thrusters the following...

Large Grid, Small Thruster: 150,000*2 = 300,000 N thrust 1.5*2 = 3.0 MW power usage
Large Grid, Large Thruster: 142,500*24 = 3,420,000 N thrust 1.575*24 = 37.8 MW power usage

My own XL Thruster out of interest would come out as...

TVSI-Tech XL: 127,500*96 = 12,240,000 N thrust 1.725*96 = 165.6 MW power usage

I'm also working on a way to offset one against the other to allow people to, for example, build a higher than normal thrust engine but offset the improved thrust against a higher power usage requirement and vice versa, thus people aren't entirely stuck to these values.



There are still remaining issues which need to be covered, mostly material cost, damage capacity and mass (which are all anyway linked as all three are dictated by the components). As states in a previous post, I think these should simply be linear per-block; we just need to work out some good values.

For example we could go with the Small Thruster values (using wiki here so they may be outdated) and use...

40 Thruster Components/Block
4 Large Steel Tubes/Block
30 Construction Components/Block
12 Steel Plates/Block (It's actually 25 / 2 so either round up to 13 or down to 12).

 

Definitely; I think they have put in some loose, rounded values for the moment to get the thrusters into the ballpark arena for planets, but I don't think they've yet put thought into balancing them against each other, let alone setting a guidelines standard for keeping larger, modded stuff 'stock'.

And yes, you are absolutely correct, power also needs to be balanced (though personally I quite like the new settings). One problem at a time though, and I'm picking on thrusters first as I have already put a lot of thought into this over the last few months, even before the changes

 

@Tristavius: I don't think "per block" is the right metric for thrusters; it just seems very arbitrary. I also disagree with the length of the nozzle being "that all important 3rd axis." A longer thruster with just about any known or theoretical technology isn't ever going to be a viable engineering option for higher thrust. You are always better off picking a thruster with more area, because it's always about how much "stuff" you can push against.

You just can't cram more material out the back of a fixed-diameter nozzle, and even with ion thrusters that can increase the energy of the exhaust flow in proportion to the length, thrust only goes with the square root of the length, so it gets very inefficient very quickly to build a thruster with too long an acceleration chamber.

I'm all for tradeoffs, but I'd like them to be at least as steep as they are in reality. So doubling length of an ion thruster (all else equal) takes twice the power but gives 41% more thrust (so about 70% the "thrust per block" you mentioned. Making a thruster 20 blocks long would cost 20 times the energy, but only give you 4.47 times the thrust (or less). Yes you could do this, but you'd be way better just taking up 4.47 times the area and taking 4.47 times the energy. No good engineer would ever choose to make a longer thruster over a "fatter" thruster.

 

Almost all real life rrocket have fairly large aspect ratios (ie they are longer than they are wide) because you need nozzle length to properly compress the supersonic flow out of the diverging section. Other than nuclear pulse propulsion we don't have any technology to make high trust space engines.

SE's thrusters are unrealistic with their 1:2 and 2:3 aspect ratios.

Something I've argued for a lot is that we need chemical, or nuclear thermal rockets that generate more thrust but are longer (ie cost more internal volume).

It's no longer a question of purely thrust to volume, but that the thruster itself needs different/more infrastructure.

In general, I just don't really like the mechanic that everything in SE boils down to reactor/battery power, with the bulk of reactor power going into electricity to power engines. There are better ways to use nuclear power for thrust in 2015, nevermind 2077.

 

I'll grant you the aspect ratios may be a little off - but the ideal physical aspect ratio is just a constant, not something that you would change to get a different thrust profile. I don't think the aspect ratio of the thrusters in SE is really a gameplay thing.

I agree with you here; I'd love to have more ability to tweak the characteristics of blocks. If I don't need the full torque range of a rotor, I want to be able to put in fewer motors. If I have a very small craft, I want to be able to skimp on the number of computers I have to put in the cockpit. If I want lower range on my antenna, I want to be able to put fewer antennae components in it.

If I don't have nickel around, I want to be able to make motors that are less efficient just using iron; they provide less torque or require more power. Stuff like that.

 

Actually the ideal physical aspect ratio is not a constant, and varies from design to design, but they are mostly in the same ballpark.

I'd also definitely like tweakable blocks. Small grid gyros are often overkill for micro-ships. I think the only thing holding it back is that is a lot of block data to manage.

 

I generally have an implicit "all else equal" in my mind when I say things - maybe I need to make it more explicit.

 

Does anyone else think a 2x boost to large grid thrust would have been better than 3x? I think that would help the small and large grid acceleration balance. The small grid seems a bit slow now, but if it were buffed, the acceleration would be too fast for the max speed IMO. I think the answer is to nerf the large grid to about 2/3 to 3/4 of what it is now.

 

Actually I think its just about right.

The large block untility ships I built now actually MOVE (with no changes) rather than crawling around painfully slow. So I can build a small block ship with 1 thruster in each direction and a large block ship with 1 thruster in each direction and they perform the same. Rather than having the small block ship move so fast I endup crashing into things, and have the large block ship move so slow, it was almost faster to carry everything by hand.
Yes the power consumption is more, but the large block reactors produced so much excess power it seemed wasteful. Now with 1 small reactor and 1 thruster in each direction its adequate.

 

Mass, mass, mass...

Performance should always be about acceleration. F=ma or better stated as a=F/m. The block size is going to be a constant due to the size of the models. What's more important is the ratio of force to the mass of the block. This is not only important for the thrusters that are firing but also to the additional thrusters in the other 5 directions that are idle while this is happening. Each thruster you add, increases the mass of the ship making each thruster that much more inefficient in terms of acceleration.

 

I would favor pulling it down even further than that; I never had a problem with how large thrusters felt in terms of gameplay, it was their resource cost that bothered me. Anemic thrust on a starter ship was fine, but shelling out many times the thruster components to repair damage to it than a small-grid tug that could haul it around would cost never made sense. Plus, I'm still fervently hoping they add those upgrade modules in; I really want to be able to take the same ship, with the same number of thrusters, and muck around in the engineering section to coax more power or more "fuel economy" out of it.

Thing is, we're really going to have to wait for planets to actually be introduced before we can say anything definitive at this point. I feel large-grid thrusters are far too powerful, but for all I know the current values are what's necessary to give any large ship that isn't completely coated in thrusters a prayer to get off planets. Granted, it doesn't sound like that at present, but I haven't tested the planets myself, not being that brave with code.

This is pretty much right on the money, though like I said, I would like to achieve that depth by means of upgrades rather than exclusively by adding more thruster variations. That said, we do need some bigger thrusters (hint hint, @Tristavius ).

 

I support clawing back large grids to 2x pre balance period values, but also reducing their component costs.

 

This is now an "old" thread, but I didn't want to lose this conversation. Since things haven't really been updated regarding (ion) thruster balance and I've been frustrated in my alternate designs, I've done some simple math and have now come up with a proposal for rebalancing ion thrusters. Ship architects will enjoy the generally improved thrust to weight ratios (fitting with square-cubed law) and reduced material requirements, but will likely balk at the higher energy requirements. Notably, the higher thrust to weight ratios for the large thrusters come at the expense of higher power requirements (more thrust per nozzle area means higher exit velocity, which means more energy per unit exhaust; hence higher power requirements).

The principle I used was to make the thrusters behave in a consistent manner - not so much anything related to gameplay or resource cost, but purely on operational parameters. Specifically:

• Structural component requirements based on surface area of the blocks
• Thrust proportional to number of thruster components
• Power proportional to "exhaust velocity", where "exhaust velocity" is proportional to the square root of (thrust divided by nozzle area)

The proposal is: