Rather ancient carriages I have made, looking for critiques

[TrabantDeLuxe]

For those who don't check UKTS:




More of the same . Did a bit of texture work on the cab.

If you are confident that your maths and adhesion algorithm are both correct, then it could maybe be your coefficient of friction is too high? Engineering Toolbox states that a coefficient of friction for a dry, clean steel on steel contact could range between 0.5-0.8, but both the railhead and the tires of the wheels are likely to be contaminated, particularly with fluids such as moisture and oil, so a lower figure would be more realistic for railway simulation applications in my opinion. I would go for 0.3 for dry conditions.

Kind regards,
Chris

I'd like to come back to this. I've done some more research, and two things came to light. Firstly, I had grossly overestimated the adhesive weight of the locomotive. I couldn't find reliable data, so I compared the weight to adhesive weight ratio of other 4-4-0's. Doing this, I came to an adhesive weight of 30 000 kg. The actual adhesive weight of the engine turns out to be 26 800 kg. Second, the coefficient of friction you'll find in period literature is quite low. Igel states 1/4, and tests by Cpt. Galton, conducted in the 19th century, give values of 0.242 at starting, rapidly dropping to as low as 0.05 at 50 mph. With these figures, and sensible approximation of rotational effort by the pistons, slips are much more likely.

[DominusEdwardius]

actually at 50mph Galton found the Coeff of friction to be around 0.118

[AndiS]

I did not see the 1/4 in Igel. The most used figure was 1/7, written as 0.14 it was a standard value in MSTS .eng files.
That could have been a bit on the pessimistic side.

There were two things to discount from what would be a possible value:

1) At low speed, the individual chuffs result in uneven traction force over time. More scientifically put, for each half-rotation, there is a point where steam is admitted (quite suddenly), then it is cut off and expansion is what drives the piston. If that does not decrease, then you got too much back pressure on exhausting. Granted, the next cylinder will jump in, but still there is some up and down in the tractive effort.

2) At high speed on imperfect track, there will be some partial loss of contact between some wheels and the tracks, for some moments.

[TrabantDeLuxe]

@ Ed: I'm going to believe you at that one - it seems more in line with more modern research. I'm trying to find the book where I've gotten my numbers from, but can't remember for the life of me where I got them.

@Andi: The question of instantenous tractive effort is a complicated one. Some things from the top of my head:

• The net force acting upon the piston changes primarily with cut-off, and speed. It is not constant through-out the stroke of course.
• Then the torque exerted upon the axle(s) changes with the rotation of the wheels and the position of the piston.
• There's a significant impact of the inertia of the bits of motion going all over the place - this is noticable at a good clip.
• These bits of motion going up and down affect the instantaneous weight on the drivers somewhat.

If I remember correctly from what I've fiddled about with this, the first two points serve to make the TE vs rotation graph a bit sinusoidal, the latter point kind of dampens that effect. Exact calculations of instanteneous TE are difficult in realtime, but approximations are possible. At high speeds however, you'll have to think about the fact that there simply aren't enough updates per rotation - i.e. players with low fps could get lucky that their peak TE is actually never considered .

[DominusEdwardius]

on the G2 I use a constant torque calculation (so the pressure and resulting torque are calculated each update) and the net force from the four cylinders calculated and applied. I start blending that out from 6mph with a more typical average force until at about 15mph the force is completely dependent on the average estimate.

[cjbarnes5294]

Damn, what a spectacular work of art! Thank you for sharing some more shots of it!

Edit: very important question - are you enjoying it from a playing perspective? Hopefully you are because what you've done so far sounds stunning.

Kind regards,
Chris

[TrabantDeLuxe]

Thanks everyone.

Chris, I've got a bit of a confession on that front: I'm not much of a driver. I've tried scripting some features to make it behave a bit more interesting (wouldn't say realistic), so it does keep me occupied. About the fun part: It still hasn't got brakes, and the test route is a few miles long. The challenge to the six-year-old in me is of course to cause the biggest pile up I can.

[cjbarnes5294]

From the level of effort and thought that has displayably gone into the dynamics so far, I suspect you do yourself a disservice and it is already pretty realistic as well as interesting. The reason I asked is purely out of curiosity; I think it's interesting because I personally don't get as much enjoyment out of the engines that I've worked on as I do when I play with someone else's loco, which I often put down to being like cooking your own dinner - it never tastes as satisfying as when someone else makes it for you! I just wonder whether that is the case for other developers, knowing how much hard work and love everyone here puts into their own projects to make it as good as they can before they start to lose the will.

Kind regards,
Chris

[TrabantDeLuxe]

Let's say it this way: I have no practical experience of firing or driving a steam engine. Driving the prototype would be a bit of an issue, unless the chaps of the A1 are looking along. So whats left is the (often complex) theory, and (often contradictory) input from those who have driving and firing experience.

I kinda get the thing about driving your own engine. I know almost exactly how the engine will respond. I also know the little things in the script that adversely affect performance. So in a way, that lowers immersion to me. After all, you're the one who's created the suspension of disbelief. I should also add, that I know where things break down a bit, both on the simulation and modelling side.

[TrabantDeLuxe]

So a while back, I made this statement.

Nah, there are some issues with the exact shape. I've got to be 100% fair here and say that there's more of these issues with the model. The boiler for instance, is a good inch too wide. The entire model is, last time I checked, a couple of inches short. However, this being intended as a freeware model, I genuinely ask myself whether I'm obliged to anyone to go and correct these issues. And besides, source material is difficult to obtain, and sometimes contradictory. It's the painting versus technical drawing story.

I was just joking. I managed to get a good set of drawings in the mean time, so decided to at least redo the most important bits and pieces. Which turned out to be practically everything.


Somehow I've never been able to get viewport AA to work...