Magic Propulsion! - A Study of KSP Collision and Reaction Wheel Physics

Recommended Posts

A note to start off: This is quite a long post with stuff that might be boring for some of you. If you just want to know the conclusion, skip to the end.

So this all started while I was reading through this thread in the game-play questions. Being a bit of a turbohead myself, I figured I could help out at least a little bit with the aerodynamic efficiency of the propellers, even if electric engine types weren’t really my thing.

As I read through, I encountered @Geschosskopf who believed from his extensive experience with Kraken and Ladder drives, as well as his (excellent as you will find out) spidey senses for potato physics that stock propellers must exploit physics somehow, his hypothesis being that they were taking advantage of some kind of artifact of the game’s collision physics that ignored Newton's 2nd and 3rd laws. The idea being that the propeller was dragging the plane along without “feeling” the plane. The very good reasons for this idea are summed up in the following argument.

“How many RTGs do you put on a shaft?  4-6 at most, maybe less?  Each RTG makes 0.8 EC/sec.  The accepted conversion rate to real units is 1 EC = 1 kJ, so 1 EC/sec = 1 kW ~ 1 hp.  Thus, you're only putting 3.2-4.8 hp into the shaft, which is the about what you get from a small lawnmower engine.  How are you even going to taxi, let alone fly, a multi-ton aircraft with that little power?” - Geschosskopf

I knew ladder drives and kraken drives took advantage of some strange physics, but I couldn’t wrap my mind around the idea that the physics of collisions between basic craft (like the propeller shaft and the plane) could be messing with things, because that would imply some very wonky effects would be seen any time two crafts were in contact. That being said, I may have been a bit biased since I regularly work on stock turboshaft helicopters.

We struck up a lively debate in a private chat, which took place over the course of 3 days. His arguments usually went into the workings of the game, looking at how it (probably) models collision, trying to insure that the collision meshes two parts on different vessels are not clipping into each-other, and moving them a bit if they are.  Meanwhile mine usually stayed more on the player side of things, using thought experiments such as a caged jet (this will be followed up on later) to show why it didn't make sense that the propeller was pulling the plane in ignorance of Newton's 2nd and 3rd laws.

Eventually I decided to actually run a few KSP experiments to determine the viability of the wonky physics idea, and otherwise determine what was going on.

The first experiment was with a Mallard carrying an orange tank. The Mallard had the orange tank inside the cargo bay mounted on a decoupler, with cubic struts and I-beams positioned around it so as to act as a cradle for the orange tank, preventing it from moving when decoupled. The configuration can be seen here.

The idea being that, if collision physics work properly, the plane should take off at exactly the same speed if the orange tank remains attached to the plane as if I decouple the orange tank and let the cradle of cubic struts keep it from moving. If the collision physics are wonky like Geschosskopf theorized, then the plane should take off at a lower speed when the orange tank is decoupled, because the game will think the plane is only lifting itself, and will only teleport the tank along to prevent clipping.

I made the first run with the orange tank still directly attached to the aircraft. I was a little late with the screenshot, but it took off at 76.1m/s.

I made the second run with the orange tank decoupled and held in the cradle. I made this screenshot on-time to see the takeoff once again at 76.1m/s. Exactly the same as the previous takeoff.

Sequential trials produced almost identical results, thus appearing to imply that the collision physics worked properly, obeying Newton’s 2nd and 3rd laws. But I wanted to be extra sure, so I devised a second experiment.

The second experiment I called the “Caged Jet Experiment”. The idea was to simulate the pushing of a stock propeller on an airframe using a jet engine. Just in the same way a prop-shaft is restrained to the airframe of a stock plane or helicopter by a bearing, a jet engine would be restrained to the airframe of a Mallard by a “cage” once again composed of cubic struts. The idea being that a jet engine would stand in for a propeller shaft. If the collision effects ignore Newton’s 2nd and 3rd laws in the way Geoschosskopf theorized, then a jet held in a cage should make the plane move much faster than one directly attached to the plane, because the jet engine doesn’t realize that it is pushing the big heavy plane.

I didn’t take many pictures of this one because I didn’t have an autopilot installed to allow me to hold a certain altitude precisely, so as to be able to quantitatively measure the performance of the plane.  However I testify that it performed nearly if not exactly the same when the engines were decoupled and trapped in the cages as when they were still directly connected to the plane.  The only difference was that with the decoupled engines, I could not reduce throttle for landing afterwards.  Good thing the Mallard was a seaplane!

Another experiment I proposed, but did not perform, was to attach a 5 ton trailer to a 3 ton rover using a stock pin-in-hole joint. If the collision physics work correctly, the setup should behave exactly like what it is. A rover pulling a heavy trailer, with all the associated performance losses.  However if the collision physics are wonky, the rover should still have the same performance as if it were driving on its own, and pull the trailer along as if it is nothing.  I’m guessing the people I see on here building semi trucks every now and then that a truck most definitely is affected by carrying a trailer behind it.

So, the collision physics didn’t seem to be the root of the problem, so another idea came up. That was that KSP didn’t know how to properly get the thrust of a stock propeller, however this was quickly disproved by the point that a propeller is quite literally a number of wings moving a circle. KSP doesn’t have to do anything to find the thrust of a propeller or lift of a rotor that it doesn’t have to do to find the lift of a plane going into a slip-turn.

So then there was my hypothesis that the 1EC = 1kJ standard was incorrect. I devised an experiment to try to prove or disprove this.

So how it went in my head was that I would measure the torque output of a reaction wheel in relation to the angular velocity. Using these values I could determine the power output by the equation power = torque x angular velocity (P = τω). By comparing this to the electricity drawn (EC/s) by the reaction wheel, I could find the energy content of a unit of electricity.

For the experiment I created a kOS script which can read the angular velocity, and use that to determine various other statistics. I also created a special vessel with which to perform the experiment

There is a probe core, a fuel tank, a reaction wheel (the 0.625m type, which has a constant electric charge draw of 0.25 EC/s), and two spider engines on the sides directed so as to create torque. The engines are a known constant source of torque, calculated to be 7740 newton-meters.

So what the script does is activate the engines, and then take a reading of the angular velocity and labels it Ang_vel0 at a time desginated T0. It then waits a short period, and measures the angular velocity and labels it Ang_vel1 and takes the time as T1.

It can now calculate the angular acceleration as (Ang_Vel1 - Ang_Vel0)/(T1 - T0).

It can then calculate the moment of inertia of the craft in the roll axis using α = τ/I => I = τ/α.  Moment of Inertia = Torque / Angular Acceleration

Note that I use the infinite propellant cheat during this experiment to make sure the moment of inertia doesn't change as the engines fire.

Anyways, so the script shuts off the engines again, since it needs no disturbances for the next part of the experiment. I use timewarp to bring the spin back to a halt, so as to have no influence from the previous bit that determined the moment of inertia.

The script now locks the ship's roll control to full clockwise (would work counterclockwise just as well, that's just what I picked), and uses the same procedure of finding angular acceleration using = (Ang_Vel1 - Ang_Vel0)/(T1 - T0). It displays this value as well as the angular velocity**

Since it now already knows the moment of inertia, it runs it the other way to find what torque the reaction wheel is producing.  τ = I*α        It displays this value**

Now with the torque and the angular velocity, it can calculate power via P = τ*ω   It displays this value**

**All these are updated over time, allowing changes to be observed

By plugging all the displayed values into a spreadsheet, I was able to create charts displaying various items such as torque curves.

Spoiler

To my intrigue, at near-zero angular velocity, the 1EC = 1kJ conversion rate was true (so in the graph I put EC/s as W for watts), but as angular velocity increased, the reaction wheel appeared to be developing more and more power from the same constant power input.  I and probably a lot of people here knew reaction wheels were broken due to lack of conservation of momentum, but this demonstrates just how badly they are broken.  At just 9 radians per second, the reaction wheel is multiplying the power input by a factor of 150. Thus you can give an electric plane spitfire performance with the electric power equivalent of dinky little lawnmower.

I have yet to perform the experiment up higher angular velocities, however it would be interesting to see how the trends continue. I want to add some more tests into the experiment as, now that I think about it, I'm wondering if torque is actually constant, and the apparent change is due to the spider engines stretching away from the tank due to centrifugal forces, thus changing the moment of inertia slightly. Perhaps I can devise a method of testing that does not require any off-axis parts.*

Current conclusion: Stock propellers in of themselves are not exploitative, however electric props take advantage of broken reaction wheel physics to generate power a couple orders of magnitude greater than what is put in!  So neither Geschosskopf nor I were entirely correct!

*Update: After further testing using a reaction wheel and a tank with no radial engines, I have found that the torque output of reaction wheels is constant. Using this I plan to calculate the MOI of numerous parts, which could be useful for the construction of mechanical contraptions.

Thanks for reading! Also thank you Geschosskopf for the fun debate and the push to question the workings of the game. This all was quite interesting to work out.

For anyone interested in examining the script I used you can find it below. The order of the display of values and their labels have been modified slightly to be more user-friendly, but all the math is the same. Not that the variable labeled "Torque" is used twice in the script. In the first section it is a fixed value, designating the torque from the two engines. In the second section it is overwritten and is the calculated torque output of the reaction wheel.

Spoiler
```//This script was created to try to determine the EC to power conversion done by reaction wheels

Stage.
Set Torque to 7740. //The torque from the two ant engines was determined to be this (Nm)

Lock throttle to 1.0.
Wait 0.5.

Clearscreen.
Set T0 to time:seconds.
Set Ang_Vel_0 to ship:angularvel:mag.
Wait 0.001.
Set Ang_Accel to (ship:angularvel:mag - Ang_Vel_0) / (time:seconds - T0).

Set MOI to Torque/Ang_Accel. //Finds moment of inertia using a known constant torque source: engines
Lock throttle to 0.
Print "Moment of inertia: " + round(MOI, 2) + " kg*m^2".

Wait 10. //Make sure to timewarp briefly now to halt rotation. Not entirely necessary but I feel it's more scientific

Set ship:control:roll to 1.0.
Until (Abort)
{
Set T0 to time:seconds.
Set Ang_Vel_0 to ship:angularvel:mag.
Wait 0.001.
Set Ang_Accel to (ship:angularvel:mag - Ang_Vel_0) / (time:seconds - T0).	//a = dw/dt
Lock Torque to MOI*Ang_Accel. 							//a = T/I --> T = Ia
Lock Power to Torque*ship:angularvel:mag. 					//P = T*w
Clearscreen.
Print "Angular Velocity: " + round(ship:angularvel:mag, 2) + " rad/sec".
Print "Torque: " + round(Torque, 2) + "Nm".
Print "Power Output: " + round(abs(Power), 2) + " W".
Print "Implied kJ/EC: " + round((abs(Power)/0.25)/1000, 2) + " kJ/EC".
}.```

Edited by EpicSpaceTroll139
Update
Share on other sites

Did you have to shoot down the stock prop plane? We'll hold you responsible if Squad ruins it. As for OP reaction wheels, I don't really care if they are OP. Cut them back and craft that use reaction wheels will suffer greatly.

Share on other sites

46 minutes ago, The Dunatian said:

Did you have to shoot down the stock prop plane? We'll hold you responsible if Squad ruins it. As for OP reaction wheels, I don't really care if they are OP. Cut them back and craft that use reaction wheels will suffer greatly.

Well, it should be intuitively obvious that stock props powered only by a couple of RTGs are still somehow delivering the in-game EFFECT of several thousand horsepower, which is silly on its face.  Thus, stock props based on reaction wheels are very clearly exploits.  They're very ingenious and fun to play with, but they're taking advantage of a loophole in how the game applies physics to reaction wheels.

Look, I love playing with such things, and ladder drives and kraken drives as much as the next person.  And I would hate to see such things removed from KSP.  So the point here isn't to advocate "fixing" such things, simply to point out what an exploit electric stock props are.

And reaction wheels aren't really "broken", simply incomplete.  The issue is, the game ignores the energy side of things, but this is because the energy side of things really doesn't matter when reaction wheels are put to their intended use, which is steering long, massive rockets with high moments of inertia.  When doing that, the RPM of the rocket is quite low, both because the torque is weak and also because high rotational speed is usually not desired by the player trying to put the nose on navball marker.  Note @EpicSpaceTroll139's 3rd graph, of power developed vs. angular velocity.  The faster you spin a shaft, the more power it requires.  However, calculations show that as long as the rocket's angular velocity under torque is no more than about 1/2 RPM, there's NO "magic" power being generated.  1/2 RPM is within the range of what most folks use in space when rotating rockets, and in step with the power drawn by the reaction wheel, so there's no point in worrying about the power required / produced at higher RPMs.  Doing that calculation would just needlessly increase the load on the CPU, so no harm, no foul.

It's only when you do silly things that take reaction wheels out of context that this lack of attention to energy becomes an issue.  Freed from the moment of inertia of the long, massive rocket, reaction wheels accelerate quickly until they hit the arbitrary max set by the game to keep itself from crashing.  That's why stock props based on free-spinning reaction wheels are exploits--the game simply lacks the math to keep reaction wheels from spinning so fast.

Edited by Geschosskopf
Share on other sites

54 minutes ago, The Dunatian said:

Did you have to shoot down the stock prop plane? We'll hold you responsible if Squad ruins it. As for OP reaction wheels, I don't really care if they are OP. Cut them back and craft that use reaction wheels will suffer greatly.

It's only electric stock props that exploit the broken reaction wheel. Stock turboprops are completely fine as far as the physics go.

I really doubt that Squad will fix the reaction wheels, as it would mean that pretty much all spacecrafts would need RCS to deal with reaction wheel saturation, and thus very people would even bother using the reaction wheels. Either that or they would repeatedly use timewarp to get rid of rotation after unsaturating the reaction wheel. The reaction wheels would also need to have large power draws to get reasonable turn rates. Seems pretty needless for a game that's supposed to be fun, and just to prevent the odd person from making a stock electric plane that exploits physics a bit.

Edited by EpicSpaceTroll139
Share on other sites

5 hours ago, EpicSpaceTroll139 said:

I really doubt that Squad will fix the reaction wheels, as it would mean that pretty much all spacecrafts would need RCS to deal with reaction wheel saturation, and thus very people would even bother using the reaction wheels....

As mentioned above, I wouldn't call reaction wheels "broken".  In the context of their intended use, they do their torque-related math without errors and there's no need for anything more complex because the angular velocities they cause on ships of the scale they were designed for are not big enough to require more power than the reaction wheels actually draw.  Thus, in their intended role as steering mechanisms, the only possible grounds for complaint is the magnitude of the torque they provide.  But really and truly, this torque is pretty lame in comparison to other things in KSP.

The size 0, 1, and 2 reaction wheels provide torques of 5, 15, and 30 kNm, respectively.  These values are measured at the rocket's CoM.  Thus, if you replace the reaction wheels with some sort of engine mounted 10m from the CoM, such engines would have thrusts of only 0.5, 1.5, and 3 kN, respectively, to provide the same amount of torque.  The Spider and Ant LFO engines, and the Place-Anywhere RCS port, all produce 2 kN of thrust, while the 4-way RCS port produces 1kN.  IOW, the torque of a single reaction wheel OF ANY SIZE is in the same ballpark as the weakest engines in the game, and single RCS thrusters, with 10 full meters of leverage.

Share on other sites

@EpicSpaceTroll139... There's no "love" button like on Facebook.

I want to marry you.

Share on other sites

2 minutes ago, Azimech said:

@EpicSpaceTroll139... There's no "love" button like on Facebook.

Hehe I believe for like a day or so after the bigish forum update there was one. Too bad they got rid of it!

Share on other sites

@Geschosskopf I do like your dedication. I talked about this topic in the main "turboheads" topic because I didn't agree with it but didn't give myself the time to give an accurate response. EpicSpaceTroll139 did and not only that, used math in the discussion. The only thing I do is visualize physics due to experience and intuition.

We're on a road together, some of us hope KSP will become more realistic as the years go by, or with a new product. These discussions help in achieving this. Therefore I want to thank both of you for the effort.

Share on other sites

26 minutes ago, Azimech said:

We're on a road together, some of us hope KSP will become more realistic as the years go by, or with a new product. These discussions help in achieving this. Therefore I want to thank both of you for the effort.

Glad to be of service   And it was a lot of fun digging into this subject with @EpicSpaceTroll139.  We're in agreement on what''s going on with electric stock props---KSP simply didn't anticipate the need to worry about reaction wheels being used as engines, so there's no accounting for the power they'd actually require to spin fast enough to move planes.  I can't say that was a bad design decision.  Seriously, the things are not and never were intended to be engines, so why bother?  Not treating them as engines streamlines the code for their intended purpose, so all is good until somebody finds the loophole.

That's a separate issue,. however, from reaction wheels being overpowered (i.e., have too much torque) in their intended use of steering rockets.  That complaint has been around since way back in the 0.whatever days, long before reaction wheel props became a thing.  My question is, if reaction wheels are no more powerful than RCS, and are thus tied for last place on the KSP machismo scale, what's there really to complain about?  If you think they're still too strong, you can always use RCS instead and problem solved.  Which is what you'd be doing anyway if reaction wheel torque gets downsized.

I find the whole argument about "realism" in KSP, and how folks get so caught up in it, rather silly.  So many folks define "realism" as "just like Earth", which is simply wrong in the context of stock KSP.  A cursory examination of the stock KSP solar system makes it patently obvious that our universe and the KSP universe differ significantly down to the level of the fundamental forces.  How else can you have a habitable planet with an average density greater than osmium?  How else can the moons of Jool be in stable orbits?  IOW, trying to impose Earthly values on things in stock KSP is less correct than leaving them as they are, because nothing on Kerbin, down the very elements of the periodic table, can be anywhere near the same as on Earth.

Share on other sites

I teach high school physics for a living, and I must say that I love reading a careful examination of a weird phenomena in any set of natural laws. That these laws are different from the ones that drive my car is just an interesting addition. Good work, we ought to have a journal for things like this.

Share on other sites

5 hours ago, Geschosskopf said:

Glad to be of service   And it was a lot of fun digging into this subject with @EpicSpaceTroll139.  We're in agreement on what''s going on with electric stock props---KSP simply didn't anticipate the need to worry about reaction wheels being used as engines, so there's no accounting for the power they'd actually require to spin fast enough to move planes.  I can't say that was a bad design decision.  Seriously, the things are not and never were intended to be engines, so why bother?  Not treating them as engines streamlines the code for their intended purpose, so all is good until somebody finds the loophole.

That's a separate issue,. however, from reaction wheels being overpowered (i.e., have too much torque) in their intended use of steering rockets.  That complaint has been around since way back in the 0.whatever days, long before reaction wheel props became a thing.  My question is, if reaction wheels are no more powerful than RCS, and are thus tied for last place on the KSP machismo scale, what's there really to complain about?  If you think they're still too strong, you can always use RCS instead and problem solved.  Which is what you'd be doing anyway if reaction wheel torque gets downsized.

I find the whole argument about "realism" in KSP, and how folks get so caught up in it, rather silly.  So many folks define "realism" as "just like Earth", which is simply wrong in the context of stock KSP.  A cursory examination of the stock KSP solar system makes it patently obvious that our universe and the KSP universe differ significantly down to the level of the fundamental forces.  How else can you have a habitable planet with an average density greater than osmium?  How else can the moons of Jool be in stable orbits?  IOW, trying to impose Earthly values on things in stock KSP is less correct than leaving them as they are, because nothing on Kerbin, down the very elements of the periodic table, can be anywhere near the same as on Earth.

One thing is for sure, I tend to avoid using reaction wheels when building an engine. In fact the appearance of propeller planes using reaction wheels and/or tip jets/rockets was the reason for me to invent the turboprop engine years ago. Now this is a completely different concept, actually being incredibly inefficient and a lot harder to get right. A lot of fun as well. Recently I also started to build "real" electric motors, another challenge and a lot less powerful.

But even my piston engines are not really realistic. I can only hope we'll have powerful enough computers one day to run fluid dynamics. If that ever arrives in KSP, my girlfriend would probably leave me because I'd be designing engines like a maniac.

In the end it's all about the choices we make. I no longer play the game, I'm just designing stuff. So realism has a different meaning for me. I wouldn't want Squad to change the game so others would suffer.

But let's hope for a future product in a different universe, one with all the physics and materials like we have on Earth.

Share on other sites

14 hours ago, EpicSpaceTroll139 said:

I really doubt that Squad will fix the reaction wheels, as it would mean that pretty much all spacecrafts would need RCS to deal with reaction wheel saturation, and thus very people would even bother using the reaction wheels. Either that or they would repeatedly use timewarp to get rid of rotation after unsaturating the reaction wheel. The reaction wheels would also need to have large power draws to get reasonable turn rates. Seems pretty needless for a game that's supposed to be fun, and just to prevent the odd person from making a stock electric plane that exploits physics a bit.

I've wondered about this since I first tried the demo -- in terms of "making it work", RCS is far simpler than reaction wheels, and coupling an inertial sensor suite (gyros and accelerometers) and simple controller (Apollo-level stuff) would allow things like "hold heading"  with pretty much the behavior we see now when SAS is coupled to active RCS.  Simple RCS was present in the X15 spaceplane, and Mercury capsule (Mercury used cold-gas systems; X15 had peroxide thrusters; hydrazine RCS was introduced in, IIRC, Gemini).  This was years before reaction wheels were practical for flight hardware.  Not really related to the thread subject, but it seems to me the Mk. 1 Command Pod ought to have a low-efficiency RCS, and reaction wheels should be up the tech tree at the level where the non-integrated ones appear.

Share on other sites

3 hours ago, Azimech said:

But let's hope for a future product in a different universe, one with all the physics and materials like we have on Earth.

But be careful what you wish for.  I came to KSP after decades of playing Orbiter and its various predecessors.  So why would I ditch something that's an actual simulation, with all the "just like Earth" stuff in its proper context, to play something so silly as KSP?  The main reason is that Orbiter, and all "realistic" spaceflight in general, is depressing.  Sure, I learned a lot.  Sure, I enjoyed the challenge dealing with the actual problems of real spaceflight.  But all that did was drive home the fact that we're stuck on this rock and will NEVER leave it, any any MEANINGFUL way, without UFO technology.  This was rather disillusioning for somebody who grew up watching the Space Race on TV and had the belief that he'd be living on a Jovian moon by now.

Thus, I enjoy KSP primarily because it's NOT "just like Earth".  I can live out all my childhood dreams of moving hundreds, even thousands, of kerbs to the far side of the solar system, and do it all within the rules established for the KSP universe.  Besides, it's a nice change to have to become familiar with a new set of physical laws.  And the scenery always changes.  If I get tired of the stock system, I can use a different one or modify the existing one.

So yeah, rather than ruin KSP by imposing incorrect Earthly values on it, I'd much rather keep it as it is.  If Squad wants to make a realistic space game, I'd prefer if they started from scratch.  And I probably wouldn't get it, simply because I've been there, done that already, and don't find it as FUN as KSP.

Share on other sites

I just hope someone doesnt use this 'information' to belittle someone in their choice of craft propulsion.. It is a game and all of it is effectively magic.

Share on other sites

1 minute ago, Majorjim! said:

I just hope someone doesnt use this 'information' to belittle someone in their choice of craft propulsion.. It is a game and all of it is effectively magic.

Agreed. Using this program should be fun for everyone.

Share on other sites

6 minutes ago, Majorjim! said:

I just hope someone doesnt use this 'information' to belittle someone in their choice of craft propulsion.

If we did that, it'd have to include the "magic" jet engines too. There are mods to nerf these things if anyone feels the need for more realism, play however you like.

Personally, I'd like to see a real stock rotator. It's an incredibly obvious thing missing from the game.
Reaction wheel powered motors, hinges and bearings made from parts not meant for it, they are ingenious and the effort involved in making them gets my respect... But I wish we didn't have to do this to get something as simple as rotating parts. The community has wanted them forever.

Share on other sites

7 minutes ago, steve_v said:

If we did that, it'd have to include the "magic" jet engines too. There are mods to nerf these things if anyone feels the need for more realism, play however you like.

Personally, I'd like to see a real stock rotator. It's an incredibly obvious thing missing from the game.
Reaction wheel powered motors, hinges and bearings made from parts not meant for it, they are ingenious and the effort involved in making them gets my respect... But I wish we didn't have to do this to get something as simple as rotating parts. The community has wanted them forever.

I myself no longer care, I just build my own. But there are two things I would like as well:

1. The ability to have them attached to the original craft instead of being a separate entity and

2. The ability to decide if the colliders are respected or not, for every specific part.

Share on other sites

On further reflection it occurs to me that reaction wheels are scary and dangerous and I'm going to try and avoid them.

Yeah, I just had another space stations shake itself to pieces because I forgot to turn torque wheels off.

Screw these things. It doesn't matter how "magic" they are - the Kraken collects on its debts.

Edited by dvp
Share on other sites

On 10/01/2017 at 10:25 AM, Azimech said:

1. The ability to have them attached to the original craft instead of being a separate entity and

This will only come from a stock rotating part.. I too will just build my own bearings moving parts ect as you know the issue is as you say the seperate craft farce and the fact they don't really work properly, timewarp for example and part count for another. It's all well and good just making a 'single' craft with moving parts we want many seperate craft working together to acomplish a goal, ie setting up and runnning a colony either on Kerbin or pro mode, on another world. Think @katateochi's old constellation video but using stock parts. That's playing!

Share on other sites

On 10/1/2017 at 3:01 AM, Majorjim! said:

I just hope someone doesnt use this 'information' to belittle someone in their choice of craft propulsion.. It is a game and all of it is effectively magic.

There's nothing to belittle about stock electric props.  They're quite ingenious to start with, plus are fun.  I guess the purpose of this thread is just to make sure everybody knows stock electric props are exploits, so don't mistakenly use out of ignorance in a game where they're trying to be as realistic as KSP otherwise allows.  THAT could not only lead to belittlement, but also ruin the user's game.

Electric props in KSP are generally "magic" anyway, even those that are part of serious mods.  None of them come close to requiring thousands of EC/sec to give the propulsive effect of thousands of horsepower.  Then there's the rover wheels.  Ever notice how the EC they draw falls off the faster they go?  That leads to the exact same huge input in power out vs. power in that stock electric props have.  If you push an unpowered rover with a jet engine and do the math based on the jet's thrust, the horsepower is within the bounds of reason.

I guess the underlying issue is that the 1 EC/sec = 1 kW ~ 1 hp standard is good for non-moving parts (batteries and the like) but the EC requirements for moving parts (rover wheels, reaction wheels, drills, etc.) is very low compared to doing the same thing by burning LFO.  So I suppose at the bottom line, you have to look at all electrical moving parts as exploits, although to varying degrees.

Share on other sites

17 hours ago, dvp said:

On further reflection it occurs to me that reaction wheels are scary and dangerous and I'm going to try and avoid them.

They're one of the worst offenders in the game, being non-saturable and stupidly powerful...

Well, except for the solar system. The solar system is pretty damn scary. I'd have to say that's where all this nonsense started.

Edited by regex
Share on other sites

Just now, Geschosskopf said:

guess the purpose of this thread is just to make sure everybody knows stock electric props are exploits,

This sentence highlights my point exactly. It is no more an 'exploit' than making a turboprop or even just using the engines as squad designed them to be used. it's a game.

Share on other sites

53 minutes ago, Majorjim! said:

This sentence highlights my point exactly. It is no more an 'exploit' than making a turboprop or even just using the engines as squad designed them to be used. it's a game.

Yeah, it's not really an exploit so much as taking advantage of a failed point of realism in the game.

Share on other sites

Just now, regex said:

Yeah, it's not really an exploit so much as taking advantage of a failed point of realism in the game.

Why do you even play KSP?  The entire concept is unrealistic.. Perhaps you would be happier playing orbiter or something of the like.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

×   Pasted as rich text.   Paste as plain text instead

Only 75 emoji are allowed.