So, you want to build a train for BVE4?
Okay, up until now we've mostly only considered the visual aspects of
the
train, and by now you should have a more or less complete set of images
in your Train\<mytrain>\d3d directory (unelss you called it
something else!). We're now moving on to the physics.
There are several aspects which affect the way the train drives in
BVE4, and all of these are dealt with a in a file called train.dat which lives in the train's
directory.
Mackoy produced a train.dat editor which has been translated into
English and which is available from TSC, along with
some other useful bits and pieces. I recommend you donwload it -
it's not the best tool for all things but it is useful for acceleration
and motor sounds, of which more later. There's also a guide to
the train.dat files, available from here which
you can also download for reference although it does have various
errors in it.
To make a good, prototypical train for BVE4 requires accurate data
about the real thing. The problems start when you look at the
data you have to put into the train.dat file, and compare that with the
data you can actually get. For example, you can quite often find
figures for maximuim tractive effort, esepcially for a loco.
However, you don't want that in the train.dat, you want acceleration in
the rather unusual units Km/h/s. So, you need to get your
calculator out, and dust off those school science books.
This is made worse by the fact that BVE is really made to simulate
EMUs. As you've probably realised by now, in BVE, each train has
its own directory, so for example the class 56 with loaded HAAs is
distinct from the class 56 empty, or light engine. The actual
differences are all in the train.dat file, but to simluate a different
consist, you need a "different" train, although all the graphics and so
on are the same.
What this means is that you need to consider the exact train you're
creating. If it's a loco, what's it hauling? If it's a DMU,
is it a 2 car, 3 car, 7 car made form a 3 and a 4, and so on. You
then need some data about the weight and dimensions of the cars (and
the loco, if it's a loco) and then you can start the calculating...
I'll run through an example that I did recently for the class 66 loco,
hauling 22 empty HTA coal wagons, which was for a diagram on the
excellent ECML: Northumberland route. You can see the beginning
of the train.dat file below, make sure that the first line reads
BVE2000000 for a BVE4 train:
First, you want the train weight. In this case, we have:
Class 66 loco: 130T
HTA wagon, empty: 27T
So, the total train weight is 130+(27x22) = 724T.
The figures for maximuim Tractive Effort (T.E.) for the class 66 are:
Starting T.E.: 409kN
continuous T.E. 260kN, at 26Km/h
Now, the formula for acceleration, a, in terms of mass m and applied
force F is a=F/m.
Using the values above, initial acceleration is 0.56 m/s²,
and acceleration at 26Km/h is 0.36 m/s². However, BVE wants
the figures in Km/h/s, which means you need to multiply by 3.6, giving
you figures of 2.01 and 1.31 to put into the train editor. Note
that these are maximum figures, so they apply to the highest notch of
the power lever, in the case of the class 66 that's notch 8. The
other thing to note about the class 66 is that it's limited to 75
mph. The loco, on maximum power and on the level, would go quite
a bit faster than that with an unladen train. The limiter is one
thing that isn't in the train.dat, it's a function of the plugin file
and that will be discussed later.
Okay, so now it's time to get that train editor out, and this is what
it looks like; in this case, I have the class 66 example I'm using
loaded:
As you can see, quite a few things to look at.
Firstly, at the top left, you can see "rate" and "adhesion" - In the
train.dat file, these are in a section headed #PERFORMANCE. Now,
Adhesion is in fact a common railway term but in some way the units
don't seem to add up if you study real-life figures. The
train.dat guide suggests that 0.9 is fantastic grip and 0.1 is very
little grip. Generally, using too low a figure will mean a lot of
wheelslip. BVE has no simulation for a sander (which real trains
tend to have for slippery conditions) so you need to err a bit on the
high side. "Rate" is for braking and we'll come back to that.
Under that, on the left, is "Delay" (#DELAY in train.dat). These
figures, in seconds, are the delay between operating the contorl and
something happening. Generally, controls are not instant.
The first two are for power: delay between moving the lever and
power being applied, and between moving the lever and the power being
reduced. The next two are for Electric brake, application and
release, and the last 2 are for application of service brakes and
emergency brakes.
R.O.C. in the train.dat is in the #MOVE section in train.dat, and these
figures are described as follows in Shaun Myers' guide:
#MOVE
120 = The amount
the train sways when accelerating.
120 = The amount
the train sways when travelling but not accelerating.
3000 = The amount the
train sways when the electric brake is applied.
3000 = The amount the
train sways when the electric brake are released.
300 = The amount
the train sways when the service brake is applied.
300 = The amount
the train sways when the emergency brake is applied.
This really
doesn't mean a lot, and that's mostly because it's probably a
mistranslation. The following interpretation is from Steve
"Trainsim" of TSC:
When we translated the Train Editor we worked out it was rate of change
of power build up/shut down and from brake release to apply and vice
versa. (Hence R.O.C in the editor).
The lower the figure - the slower the
reaction.
Traction+ is the time taken for power to build up after moving power
handle.
Traction- the time taken for power to drop a notch or to go to idle.
ElBrk+ time taken for brake pressure to go from release to full (IIRC
any brake except straight air)
ElBrk- time taken for brake pressure to go from fully applied to full
release.
BPr+ )Same as above for straight air perhaps?
BPr- )
Which makes some more sense; they combine with the "delay" figures - so
when you go from Neutral to full power, firstly there's a delay defined
in #DELAY for the power controller, and then the power builds from zero
to maximum as defined by the Trctn+ parameter in ROC. In the same
way, ElBrk+ defines how long it takes the brakes to build brake force.
Don't (yet) know what the units are, but they would appear to be
reciprocal time, since a smaller number makes a slower reaction.
Have a look at what other people have used. Puttgin silly-big
numbers like 1000 doesn't make it react a lot faster, so I guess it's
non-linear - if it were linear, 1000 would make the train hit full
power almost instantly!
Next, you have brake type. "straight air", as used on the class
66, is not what is commonly understood, in the UK at least, as
"straight air", since it applies the train brakes as well. It's a
non-self lapping brake, and has only 3 positions, bascially, these are
increase pressure, lap (hold pressure) and reduce pressure. This
kind of brake is uncommon on passenger trains now. The other 2
kinds of braking in BVE are "electro-pneumatic, sefl lapping" and
"electronically controlled pneumatic, self-lapping". Frankly,
they both look the same, you have a brake control with different
positions. In addition, there's the option of turning on
regenerative or rheostatic braking. Both of these apply electric
retardation to the train at higher speeds, and there's a control speed
where the electic braking is switched off as it ceases to be
effective. The difference between these two is explained in the
guide:
Regenerative/Rheostatic brake:
0 = Off
1 =
Rheostatic,
uses electric braking until control speed is reached then activates the
service
brake automatically,
2 =
Regenerative,
uses electric and service brakes until control speed is reached then
uses service
brake only.
although I can't
help thinking that in terms of meaning, they look the wrong way
round. Regenerating means that you're feeding power back into the
electric lines (as the class 390 pendolino does), and applies really
only to electric trains, and I wouldn't have though you'd want service
brakes as well.
After brake type, you have "Pres", #PRESSURE in the train.dat file,
these are fairly self-explanatory: maximum normal brake pressure,
maximum emergency pressure, minimum and maximum reservoir
pressures. The last 2 are used for switching on and off the
conmpressor sounds.
Next over is a panel called "Safe", which in the train.dat is
#DEVICE. Basically, for a UK train, you want it as the example:
ATS-P and ATC off, EB is the vigilance or deadman device. Not
sure if Brake
hold by itself does anything, but enable that and speed hold and the
first of your brake steps becomes "HB" which keeps the train at the
current speed when going downhill. Re-adh is traction control,
set it to the appropriate kind, (DMU, EMU, Loco - light is for such
things as tramcars), and error pass alarm should be "none". Load
compensation is supposed to vary the brake pressure depending on train
load - however, it probably only works on passenger trains as it seesm
to interact with the value for train load in the .sta command in the
route.
The controls section is better edited in a text editor in train.dat, in
my opinion - train editor tends to mess it up. You should also
check that it's right after using TrEditor. The sections are
self-explanatory, the section in train.dat is called #HANDLE and has 4
values: Note there's something about you can only vary the
"handles" part if you've got regen braking set - hence why it's greyed
out in the example above. However, it's easy to edit in a text
editor.
#HANDLE
0 = Control type.
8 = Number of power steps.
6 = Number of brake steps.
0 = Number of steps required to reduce power
The first one is
0 for 2 handles, 1 for 1 handle. Normally, you'll leave the last
one on 0 - if you set it to (say) 2, then you have to back off more
than 2 steps before the power reduces. Don't see the point in
that, myself.
The last 2 parts are cab and cons. Cab (#COCKPIT in train.dat) is
the location of the driving position, in the normal XYZ co=ordinates, X
measured from the centre of the running rail and Z from the front of
the train.
Cons is the train consist, called #CAR in
train.dat. The top two figures are the weight and
number of powered cars, the bottom pair are the unpowered cars.
"Motor" means whether the leading car is a motor car or
not. All cars have the same length, so you may
need a correction if you're simiualting a train of short
wagons, say. In the case of the 66 and the 22 coal wagons, the
HTAs are 17.8m long, so not as long as the loco. 22
of these have a combined length of 392m, so to correct the
train length we divide this by the loco length and take the nearest
round number, in this case, 19 cars of 20.1m.
The train length is relevant to things like how soon after passing a
speed limit board you can increase speed.
That's all now except for the acceleration and braking. If you
click "Accel. curve", you'll get the accleration window, which
looks like this:
This one is for the 66 coal empties again, and I've selected notch 8,
which is the highest one. If you're only using 6 power nothces,
then you'd select 6. The figures on the right come from the
acceleration figures worked out earlier. The 4th and 5th figures
determine the "tail end" of the curve: 110 km/h is where it stops being
a curve and starts to decline and 3 is the rate at which it declines
from then on. 4 is the maximum (steepest drop-off) and 1 gives a
long tail. In the case of the 66 it has a limiter at 75mph (about
120kph) and so it's more or less irrelevant. On trains without a
limiter, you can use this part of the acceleration curve to control the
maximum speed on the level: suppose the train is flat-out at 90 mph
(144 kph), you arrange for the highest notch acceleration to tail off
to nothing at a bit over 140. The lesser notch curves are
arranged to give less acceleration and less top speed - within reason,
you can do more or less what you want with them but it makes sense to
have them more or less looking the same as the full-power one.
There's limited scope for messing around with these curves as the
algorithm is built into BVE. However, there is some scope:
Below is a set which I created for a light engine version of 37901, in
consultation with a Man Who Knows how the loco performs in real life -
it's been reported that it's not far off.
This set are not based on calculation but on trial and error and on
information about how the train behaves - 37901 takes off slowly from
rest but once rolling the acceleration picks up and peaks around 40 mph.
The final thing to set in train.dat (apart form the sounds, which are
going to be covered later) is the braking. This one is very
diffcult to get enough data about. Loco data some times has brake
force in tonnes, but that may not include the train brakes - with
continuous-braked trains the maximum brake force depends on many
things, so a heavy train will sometimes out-brake a light engine, just
because it has a much higher number of brakes. Indeed, when
towing dead engines around, you often see a few coaches included in the
consist to increase the brake force available.
There are 2 options on the matter of how much brake you build in.
One is to talk to drivers who've driven "your" train and see if they
can give you an idea of how long it takes to stop from a given speed -
more or less any such data can be used - suppose you find out that the
4-car train you're modelling, if you apply service brake notch 1 out of
3 (commonly known as B1) from 30 at the end of the platform it comes to
rest nicely on the 3/4 car marker board. You then try a value for
"Rate" (the first value in #PERFORMANCE in train.dat), take the train
for a drive and see if it stops the way it should. If it's not
stopping fast enough, make "Rate" a bit higher, if it's too violent,
make it lower.
The other way to do it is to hunt around the BVE world 'til you find a
train similar to yours, and copy the value used on that. As with
everything, if it's a long way off, people will soon tell you, and you
can always release an update to address such issues.
That's about it for train.dat. Part 8
will consider the config files which actually make the train work in
BVE4.