[0.15.18] Trains with leading Fluid Wagon have low speed

[millisa]

Brief description:

A train that only has locomotives in the rear and have a fluid wagon in front will run substantially slower than a train with the positions reversed. Further - a 2 length trains that consists of a fluid wagon, with a single locomotive pushing it, will top out below 50km/h (on manual or automatic). Adding a non-fueled locomotive to the front of the train facing the same direction will allow the train to hit 200+ km/h and accelerate as expected.
The fluid wagon being empty/full appears to have little impact.

I noticed this is version 0.15.16 on osx, and was able to replicate it on windows 10.
This occurs in single player and when setting it up on a headless server.

Adding additional locomotives pushing in the same direction does not improve things (I tried with a half dozen pusher locomotives behind a single fluid wagon and don't recollect getting it over 50km/h).

Factorio Versions observed in: 0.15.16, 0.15.18 (all vanilla, no mods)
Factorio OS observed in: OSX, Windows 10

Slow in acceleration and top speed (1 locomotive pushing 1 empty fluid wagon):

GoofyTrain-Fluid-Slow

factoriobug-goofytrain.png (1.27 MiB) Viewed 3559 times

Accelerates as expected and top speed gets over 200kmh (1 locomotive pushing 1 empty fluid wagon and 1 unfueled locomotive in front):

GoofyTrain-Fluid-OK

factoriobug-goofytrain2.png (1.46 MiB) Viewed 3559 times

Possibly related to air resistance issue fixed in 0.14.10? (viewtopic.php?f=3&t=33522) "Fixed cargo wagon air resistance being smaller than that of the locomotive."

[kovarex]

The description is correct, but I don't see where is the bug. The fluid wagon has bigger air resistance.

[millisa]

I guess I wouldn't expect the air resistance to be much different by placing a non-functioning engine in front of the fluid wagon.
It is a difference of a 40km/h top speed for a train comprised of a single pusher loco and a fluid wagon, and a 200km/h top speed for the same train with a non-functioning locomotive in front. Placing an empty cargo wagon in front of the same train also allows it to reach 200km/h.

If it is working as intended, I guess I'd argue the air resistance figure may be too high. Regardless, thanks for the prompt attention/thought.

[kovarex]

The resistance is defined in the prototype, and only the front vehicle matters. The fluid wagon has almost 10 times compared to the locomotive, which might be little too much, but who knows.

[leoch]

I guess that's why my fluid train is so stupidly slow

I have a

Code: Select all

<EE EE> OOO OOO

train (push/pull engine, two fluid wagons), and its top speed in one direction is 42 km/h. I'm actually using a mod which makes the capacity smaller and weight equal to a regular wagon, so I expected it to be fairly fast!

Sounds like you're using a really basic air resistance model...

[leoch]

Actually, I find 42 km/h is the max speed in either direction. Moving one engine to each end fixes it (max speed > 100).

[TruePikachu]

According to a note in the prototypes, the air resistance is a factor of the speed that is subtracted each tick.

[leoch]

Hmm, but a '<EE EE> OOO OOO' train is slow in both directions, not just when going "backwards", so definitely a bug. Besides which, this much slowdown due to air resistance is ridiculous.

[mrvn]

Hmm, but a '<EE EE> OOO OOO' train is slow in both directions, not just when going "backwards", so definitely a bug. Besides which, this much slowdown due to air resistance is ridiculous.

Sure it is an '<EE EE> OOO OOO' train and not an 'OOO OOO <EE EE>' train? What I mean is that the front of the train could be at the back the way it is currently driving. Maybe you get the air resistance from the same wagon no matter what direction you drive?


As a side note: Why does a fluid wagon have so much more resistance than a normal wagon? Shouldn't they be the same? Or fluid even better because it is round while the normal wagon is a box.

[millisa]

From the 0.15.20 patch notes:

Reduced fluid wagon air resistance from 0.05 to 0.01

Thanks for the consideration!