Change top speed behaviour of trains

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BurnHard
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Change top speed behaviour of trains

Post by BurnHard » Sat May 24, 2014 6:46 pm

At the moment, the top speed of trains depends of how many waggons you attach. There is no logical reason behind the massive speed penalty.

In fact, it should only affect the rate of acceleration. Longer trains should take longer to accelerate, BUT they should be able to reach high speeds as well. Top speed is limited by mechanical limits of the waggons/engine AND the drag (from air and friction from wheel/rail), both are more or less independent from the lengh of the train (yes not completely, but absolutely negligible compared to the HP of the engine and how much power is needed to accelerate)

Discuss :)

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Re: Change top speed behaviour of trains

Post by Teurlinx » Sat May 24, 2014 7:14 pm

You have a point, but the weight of a train also determines deceleration (braking). Maybe the top speed is capped for longer trains so they can - more or less - realistically stop for a signal.

More robust ties of train weight to acceleration & fuel consumption would be desirable, but it might also greatly complicate signal setups.

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Re: Change top speed behaviour of trains

Post by BurnHard » Sat May 24, 2014 7:45 pm

So it happens as in reality every waggon has brakes of its own :D So if 1 or 100 waggons the rate of deceleration (braking) is the same :)

In fact it's just a thing of balancing it the right way. Everyone is able to build short trains if he wants to and need the fast acelleration. But for really long segments, where slower acceleration pays of with long moments of high-speed travel, you want to work with longer trains.

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Re: Change top speed behaviour of trains

Post by Teurlinx » Sat May 24, 2014 8:42 pm

BurnHard wrote:So it happens as in reality every waggon has brakes of its own :D So if 1 or 100 waggons the rate of deceleration (braking) is the same :)
In fact it's just a thing of balancing it the right way. Everyone is able to build short trains if he wants to and need the fast acelleration. But for really long segments, where slower acceleration pays of with long moments of high-speed travel, you want to work with longer trains.[/quote]

Not every wagon has brakes. Especially in coal powered trains you'd not find many wagons with brakes. But even if they have, a heavier train will have a longer brake distance. Just compare average brake distance of a long coal train vs. a passenger train ;)

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Re: Change top speed behaviour of trains

Post by BurnHard » Sat May 24, 2014 10:54 pm

Teurlinx wrote:Not every wagon has brakes. Especially in coal powered trains you'd not find many wagons with brakes. But even if they have, a heavier train will have a longer brake distance. Just compare average brake distance of a long coal train vs. a passenger train ;)
Do they really have? Mass (weight) should not be the limiting factor in braking speed, but sure some trains may have their reason to have less brakes build in. Thankfully a 40 ton truck has the same breaking way than a 500kg car :)

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Re: Change top speed behaviour of trains

Post by Chthon » Sat May 24, 2014 11:09 pm

BurnHard wrote:
Teurlinx wrote:Not every wagon has brakes. Especially in coal powered trains you'd not find many wagons with brakes. But even if they have, a heavier train will have a longer brake distance. Just compare average brake distance of a long coal train vs. a passenger train ;)
Do they really have? Mass (weight) should not be the limiting factor in braking speed, but sure some trains may have their reason to have less brakes build in. Thankfully a 40 ton truck has the same breaking way than a 500kg car :)
Do you really think that? Having been taught to drive busses in the military, they require far more time to stop, and lower speeds to turn safely. This is due to the fact that they have the similar amount of maximum fricative force as a car. 18 wheelers have more by 4.5x, but carry far more weight as well. The result is that they can lock their wheels and lose friction much more easily than a car. In other words, you can have all the power to stop the turning of the wheels you want, but once you lose your grip on the road, you aren't stopping.

The same goes for trains. As a result, heavier cargo trains it was discovered needed more pairs of brakes in order to stop in a reasonable distance than passenger trains. As a result cargo cars usually have their own pair of brakes, while passenger cars usually do not. This also does not mean that cargo trains can stop faster, or even at the same rate as a passenger train. Passengers cars aren't packed to the gills. Passengers also weigh far less than liquids or solid cargo options. This results in heavier trains needing to slow down in populated areas in case they need to stop.

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Re: Change top speed behaviour of trains

Post by Teurlinx » Sat May 24, 2014 11:24 pm

Another example to illustrate this: speed limits for heavy vehicles are lower than those of lighter vehicles. You can see this on your highway as well as on railways.

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Re: Change top speed behaviour of trains

Post by BurnHard » Sun May 25, 2014 11:03 am

Lower speed limits have to do with the damage the moving mass can cause. Within small limits brakeways are the same:

http://youtu.be/UL7A6Fb8AGw?t=2m2s

and several other videos... Dont want wo say an older truck has the same decceleration than than a modern race car, but in normal (european??) traffic they are (even fully loaded) not worse than cars and have really good brakes.

http://youtu.be/1Db5JpglbKw?t=20s
http://youtu.be/k3fvROZgfoA?t=12s

Everything else is just bad material and old/bad construction/design of the trucks and wrong tire material.
Last edited by BurnHard on Sun May 25, 2014 11:20 am, edited 3 times in total.

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Re: Change top speed behaviour of trains

Post by Neotix » Sun May 25, 2014 11:07 am

It's because of engine power limitation. With more weight, motion resistances are rising so if you have constant engine power output, you can't reach the same speed.

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Re: Change top speed behaviour of trains

Post by Teurlinx » Sun May 25, 2014 12:10 pm

BurnHard wrote:Lower speed limits have to do with the damage the moving mass can cause. Within small limits brakeways are the same:

http://youtu.be/UL7A6Fb8AGw?t=2m2s

and several other videos... Dont want wo say an older truck has the same decceleration than than a modern race car, but in normal (european??) traffic they are (even fully loaded) not worse than cars and have really good brakes.

http://youtu.be/1Db5JpglbKw?t=20s
http://youtu.be/k3fvROZgfoA?t=12s

Everything else is just bad material and old/bad construction/design of the trucks and wrong tire material.
The question if speed limits for trucks are still up to date, or could go up with better brakes is an interesting one, but certainly off-topic. :lol:
Neotix wrote:It's because of engine power limitation. With more weight, motion resistances are rising so if you have constant engine power output, you can't reach the same speed.
(in-game:) This can't be how it works in Factorio atm though. Weight is not a factor. Full trains move equally fast as empty ones.

(in real life:) I admit that physics classes are some years behind me, but how is weight a factor in achieving a lower top speed? I think you are confusing acceleration and speed here. Acceleration scales with mass ( a = F/m), I don't see how velocity does. Top speed seems to have to do more with engine RPM, gearing, tire diameter, drag coefficient, gearing friction, etc.


v = (2 * P / c * D * A ) ^(1/3)

v = speed (m/s)
P = power (W)
c = drag coefficient (-)
D = air density (kg / m^3)
A = surface = height * width (m^2)

This doesn't take in account the rolling resistance which will be higher with higher mass, but the main factor seems to be higher air resistance. In practice I bet it's almost entirely explained by trucks having less power per mass and the gearing. A full truck should go as fast as an empty one - ignoring various minor resistances - it would just take longer to reach that speed.


Feel free to correct me though :geek:

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Re: Change top speed behaviour of trains

Post by JackGruff » Mon May 26, 2014 12:42 am

I don't see how weaker breaking trains would even have issues with signals, they just have to break sooner.

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Re: Change top speed behaviour of trains

Post by Teurlinx » Mon May 26, 2014 4:25 am

JackGruff wrote:I don't see how weaker breaking trains would even have issues with signals, they just have to break sooner.
The problem lies with the distance between signals. In other words the size of a block. Heavier trains will need larger blocks to be able to stop before a red signal. ;)

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Re: Change top speed behaviour of trains

Post by MF- » Mon May 26, 2014 8:44 am

Teurlinx wrote:
JackGruff wrote:I don't see how weaker breaking trains would even have issues with signals, they just have to break sooner.
The problem lies with the distance between signals. In other words the size of a block. Heavier trains will need larger blocks to be able to stop before a red signal. ;)
Exactly.
It could easily happen, that such train would have to start braking many signals before the actual red signal.
But you can't know you'd like to stop on the 5th signal from where you are now,
since there are other, potentially lighter, trains that change those signals.

So... perhaps the top speed on long segments could be increased easily, but that's probably too complex.

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Re: Change top speed behaviour of trains

Post by BurnHard » Mon May 26, 2014 8:52 am

MF- wrote:... But you can't know you'd like to stop on the 5th signal from where you are now,
since there are other, potentially lighter, trains that change those signals.
When all trains - independent of length - have approx the same brakespeed, this would be no problem at all. By the way, thats all just minor mathematical "problems" if the train has to stop before reaching top speed, well. then it just doesn't for that track segment (reaching top speed ^^).

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Re: Change top speed behaviour of trains

Post by ssilk » Mon May 26, 2014 10:14 am

Teurlinx wrote:
JackGruff wrote:I don't see how weaker breaking trains would even have issues with signals, they just have to break sooner.
The problem lies with the distance between signals. In other words the size of a block. Heavier trains will need larger blocks to be able to stop before a red signal. ;)
This is tricky. I watched this very long for very long track and it works like so:

The train seems to calculate it's braking distance. This distance is "added" in front of the train. It's just as if the train begins earlier. The signals in that area are "occupied", which means they will reserve the track. That means also, that some signals in front can become yellow. Not only the next. If a signal in front is red when this imagined train-top cross, the train immediately begins to stop. Even if the signal meanwhile get back to green again.

The braking is in reality similar to weight and lenght. I knew some locomotive driver and all told me, that braking a heavy train is much more difficult, than a light one. And long trains are also complex. It is just not like in a car. You need to fill a system of pipes with compressed air and you cannot just put all in at once, because that will make the wheels blocking and that is very bad. With filling the air into the braking system, the pressure in the air tank sinks and then you can slowly open the valve more and more. So, braking with a heavy train takes just more time, because of this type of regulation. Even automated it just takes this time, you cannot speed this up very much.

So forget about the physics: it's a regulation problem. If it would be possible to bring the optimal breaking power to all wheels in the same time, the train would stop nearly in the same distance.

http://en.wikipedia.org/wiki/Railway_air_brake
http://de.wikipedia.org/wiki/Druckluftb ... Eisenbahn)
Especially this and the graphics beside it:
http://de.wikipedia.org/wiki/Druckluftb ... chleuniger

So much to this.

My opinion about the acceleration of train is, that it should be very dependent on the load. Of course also the length, because every wagon has a weight. Petroleum gas is much lighter then crude oil...

In my opinion also curves should play a role. And when it runs through a train stop it should slow down a bit.

On the other hand, for a track, which is long enough and has no curves the train should become much faster then yet (double top speed?), but it takes some seconds (I think to 10 for a light and 20 for a heavy) to speed up so fast. The top speed of a heavy and light train should be somehow identical, but the heavy one will just take much longer to accelerate and brake, than the light.
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