PlayStation (major) Ac4400 Dynamic Brakes Behaving Incorrectly

There is a serious problem with the dynamic brake behaviour on the AC4400 on PS4.

The braking force decreases as speed increases and increases as speed decreases. This is contrary to what is supposed to happen.

This leads to it being impossible to hold a steady braking force at anything other than a very low speed with the dynamic brakes, because as the speed increases slightly, the braking force decreases and cause a further increase in speed. If the speed decreases slightly the braking force increases and the speed continues to fall. On the heavy grain train for instance there is the strange situation where you can hold the train at lower speed than 8mph with a large brake force being applied in notch 3 but on the same grade be unable to hold it at 20mph on notch 8, where the braking force quickly diminishes as the train gets faster beyond around 12mph.

With dynamic brake systems the maximum braking force is at around 24mph and reduces as the train gets slower. On the AC4400 on PS4 the opposite is true. It is very broken.

The dynamic brakes on the SD40, for example work as expected, with the amps, and therefore the braking force, rising as speed increases.

This needs to be investigated by DTG (and fixed) but I would also like to know if there is the same problem on PC and xbox and for other players to report if they are getting the same incorrect behaviour from the AC4400.

 

I'm pretty sure it's the same on PC

 

No

 

I haven't found this to be the case on PC. I have found it takes time for the force to build up (as expected same as when you apply the throttle), but I haven't experienced what the op is stating is happening on console.

 

...nice write-up on this issue, glad you filed something here on it. Even if this is an issue that just affects a single platform (let alone all platforms), that’s still a whole lot of players.

 

Thanks. After first encountering the issue, on my first run with a pair of AC4400 locos, I then put a lot of effort into investigating exactly what was happening and comparing it to the braking forces quoted in literature and I’ve confirmed that the relationship between braking force and speed is reversed in the simulation. The braking force is actually shown on the HUD and loco screen rather than amps (like older locos) so the figures were easy to compare.

 

I think I have captured the bug you're speaking of on Xbox. In the video i've embedded I have 2 AC4400CWs pulling a 5,000ton loaded coal train. You can see i'm currently descending down a 1.5% grade with full dynamic brakes applied. As the train picks up speed you can see that dynamic braking force steadily decreases causing the train to accelerate faster. I think that in reality it should be the opposite, as the wheels spin faster they should generate more electricity and dynamic braking force should increase.

 

1. Is this a DPU train?
2. Maybe, is this because that only dynamic braking with this heavy train is not enough?
3. Apply some air and watch the result then.
4. I think this is a klb balance in total vs other forces e.g. the gravity
5. It is impossible to dynamic-hold 5k tons with a pair of locos downhill to Cumberland.
6. The same thing is with a throttle - try to swap to notch 1 uphill with this train and observe the numbers

 

In this case I think the dynamic brakes are working as intended because you have a lot of braking force showing, and above 24mph the braking force will decrease in reality. On PS4 I was getting full braking force at 10mph and then it steadily fell away as the speed increased. I could try and capture a video of it to compare. I might not be able to it over the next few days, I haven’t got time to do it.

 

1. This is not a DPU Train, there are only 2 units at the front, none at the back.

2. The issue isn't that the train isn't slowing down, it's that the dynamic brakes don't seem to be operating as they should. The faster the train is going the greater the dynamic braking force should be applied because the wheels are spinning faster and thus generating more electricity. For demonstration i'll embed a video of me going down a 1.7% grade in an SD40-2 with full dynamic brakes applied. In this video i'm a pulling a 1,000ton manifest train so please let me reiterate: The purpose of the video is to display the braking force, not to show the train slowing down. In this video you can see that as the train loses speed, the dynamic braking force decreases, this because the wheels are spinning slower, and thus generating less electricity.



3. I don't think that anybody here is arguing that dynamic brakes alone should be enough to hold a 5000ton train going down a 1.5% grade. The point that's attempted to be made is that as the train speeds up, dynamic braking force should be increasing not decreasing.

4. I would absolutely love to test your theory. In the following embedded video you will see me operating a AC4400CW pulling a 4000ton intermodal train up a variable grade hill (it's between 3-7% grade) with the throttle set to notch 1.



5. In the above video you can clearly see that the trains throttle is set the notch 1 the entire time. You can watch as the train slows to a halt and then starts rolling back the Klb reading stays solidly at 8Klb. I think that this proves pretty clearly that the Klb reading is the amount of force (acceleration or braking) that the locomotives traction motors are generating, and not a reading of balanced forces between the train and gravity. You can see the Klb reading in the HUD matches the reading on the Integrated Function Display. I would be suprised if a locomotive from the 90's was advanced enough to calculate the amount of force generated by the locomotive balanced with environmental factors like, grade, gravity, surface resistance, rolling resistance. More likely this is just a display of force exerted by the traction motors.

 

Don't know, maybe U are right. If there is a difference between AC and SD loco - U got IT for sure

I will play with it out of curiosity, because maybe I do feel something stabbing in my brain when using Dynamic Brake in AC? Usually it's probably Ok. on PC.

EDIT: train's behavior seems to be Ok. but I'll check the 'numbers'

 

I'm genuinely curious as to why you say that dynamic braking should generate less braking force as you accelerate past 24mph when to me it seems like in theory when dynamic braking reaches its maximum force at any given speed, that force should either stay the same or increase at higher speeds, not decrease.

 

You reach the maximum efficiency of the dynamic brake system. It’s in the table below under Standard range for 6 axle locomotives. Even with extended range dynamic brakes the braking force starts to fall at the higher speeds. For an example of how wrong the AC4400 is on PS4 I was getting over 90,000lbs of braking force in notch 3 at 5mph but something like 14,000lbs at 25mph on notch 8

 

What's the source? Tasty, I'm interested

 

It’s from a Norfolk Southern Engineers Training Handbook I found on the internet. Sorry I can’t provide a link, never thought to bookmark it.

 

...I found some other reliable info on the web that stated that dynamic brake effort *starts out* at min effort at 0mph and rises from there to max braking effort at 20mph or so. So yeah- if you’re seeing max dyn brake effort at lower speeds and lower dyn brake effort at higher speeds, then it looks like this is completely backwards vs. how these brakes operate in real life.

And I guess this only affects consoles right now- is that both consoles or just the PS4?

 

...on your point- I’m also not sure that the braking effort actually falls (or should) once it reaches its peak at 20mph or so. Based on the info I just dug up, I don’t see any mention of that happening. Separate from that, if Stu is getting a higher dyn brake effort at 5mph and a lower amount of dyn brake effort at 20mph, that would definitely seem to be a problem.

 

This problem is also a thing on pc, I just encountered it on the powering America part 2 scenario and was slightly confused

 

My PC observations:

Single AC loco train - proper behavior and numbers
MU AC train - hard to judge behavior and the wrong numbers, like U said

I'm curious to build DPU but without MU on either ends and to check.

 

where are the dynamic brakes on the ac4000 i know the is automatic brakes and independant brakes but i dont see dynamic ones

 

throttle lever integrated

 

As Stujoy correctly pointed out, this behavior is prototypical. P = F * v, for a constant brake power the force will decrease with higher speed (v). I don't know if the maximum brake force (or the klb rating) is correctly converted into braking force though, but to check that you would need to know the weight of the train and what klb value is necessary to hold the speed of the train at a specific grade (F = mg * grade/100).

 

It is not a bug or problem. The train works well. The dynamic brakes only operate on the locos engines. As soon as the complete train starts the downhill, the rollingstock (maybe 35 or 40) will start to push down the locomotives for this reason the dynamic brakes seems to lose efficency, you need to help the train with a bit of automathic brakes too. You need to stabilizate the train just practice. You your case the rain doesn't help for this reason you need to applicate much brake force. It depends from how many locomotive you have and in which configuration too. If you need more clarification i can help

 

Welcome to the thread. Please see my other comment above.

We've already reached the conclusion that the dynamic brakes are working correctly in my clip. The clip was showing the reduction of braking effort at higher speeds, the train not slowing down or maintaining speed was not the focus of the clip.

 

I know how dynamic brakes work and they work as they should on all the other locomotives. On the AC4400 on PS4 the relationship between wheel rotation speed and amps generated is reversed, giving maximum amps (and therefore braking force, as shown on the HUD) at very low speeds and hardly any amps at moderate speeds. The video in the thread doesn’t show the problem as it isn’t from PS4. I can’t put a video up of the issue at the moment. It is a real bug though.

The problem now is that the bug is unlikely to be fixed as not enough people will report it (because dynamic brakes are hard to understand when they are working let alone when they are broken) and it’s the number of people who complain not the severity of the issue that counts.

 

I'm a bit late to the thread but you stated that the dynamic brakes should generate more force with higher velocity. This would imply that the available power is increased with speed (P = F * v, if both increase then so must P). I'm not an electrical engineer but I have some understanding of E&M: If you (in theory) increase the force enough for a constant speed or increase the speed for a constant force you will at some point have equal power in the dynamic brakes as in the traction motors. Because these are basically one and the same (the traction motors turn into generators when the dynamic brakes are used, the power generated is dissipated as heat in resistors) you cannot simply increase the power from the dynamic brakes arbitrarily. You would need to upgrade the equipment to achieve this. In fact, in practice the dynamic brake power is usually lower than the traction power.

Basically the dynamic brake force curve is linear from zero up to about 1 mph then it is constant until F * v = P and then it decreases as 1/v.

You seem to know this already so I must ask what the supposed bug is about? I am somewhat confused by this thread because Stujoy who made the thread seems to think that the dynamic brakes work correctly??

 

I’m confused as to what you are saying. The bug isn’t shown in the video above, there is no video here showing the bug. I started the thread and explained the bug in that first post. The power for braking in the dynamic brakes comes from the traction motors, so it is impossible for there to be more braking force generated at very low speeds than there is at higher speeds. The bug is that the dynamic brakes are creating huge braking forces at very low speeds and very little at the speed at which they should be the highest, 24mph.

There is a chart I posted above that shows the available braking force at various speeds. Imagine that chart with the braking force column turned upside down, that’s what’s happening when the bug occurs.

 

Unless the "higher speed" is something like 60mph, then it could be reasonable that the brake force is lower than at 5mph (in the case of extended range dynamic brakes).

Nit picking aside, "For an example of how wrong the AC4400 is on PS4 I was getting over 90,000lbs of braking force in notch 3 at 5mph but something like 14,000lbs at 25mph on notch 8" definitely sounds incorrect, and I agree with you that this seems like a bug. I was confused because reading the thread and especially your comment with the tables, it looked like you were describing prototypical behavior, I now see that you were describing the video *not of your system* as being correct.

The AC4400 is an AC locomotive so it should have high brake force down to quite a low speed (maybe max force at around 5mph or maybe even lower if it is like the SD80Mace), but it should not drop off to ~ 15% of maximum at 25mph, that would imply a braking power of only ~ 1000 hp. More reasonable would be something like 70'000-80'000 lbf. Also, if you were getting 90 klbf at notch 3 then that would give the maximum brake force as 240 klbf or twice that of the tractive effort.

 

I'm a real engeneer and i drive trains in real life but in italy. However out trains are really similar to the german ones. My suspect is that the game HUD simply show what the train display say. I think that it means how many traction force (reverse or normal) the train applicate in that moment. I have tried the sand patch grade again theese days and driven some heavy cargo on the downhill with the 4400 and until 1.0% of grads they works perfectly. However for more grade you need to help them with automatic brake, so i can say that they works good. (It was a ~7000t with coal and just 2 locos in front). What you say is perfect this is how the dynamic brakes works (depends from the train too) but you can see what i mean with the br 185 in the german route. At 80 kmh you can apply a 100% of power but you can see on the hud (and in the train display) that the indicator decrease during the time, not because the train applicate less power but because the traction force decrease at high speed (or near the loco speed limit) so i think that this is the answer because i know the common base of the amarican locos but i don't think honestly that a 4400 horsepower loco with a full throttle just say "50" or "60" and the gp38 that has an half of power arrive to "800" on the hud. So i really think that it just say the traction force that the engine are appling in that moment and it says in "%" too. We need to find a real engeener from csx to know it. However i can confirm that the brakes works perfectly. ( sorry for my bad english, i'm italian but i'm trying to speek and write better)

 

I think, in many respects the HUD is a simplification and the result of several parameters, the brakes seem to behave correctly and I would not dare to question the statements of a man from the industry - delucadomenico2009 - while observing the displayed values of 'MFD' in non-lead MU loco does not fill me with optimism during downgrade. In my opinion, these values are incorrect.

I'm terribly jealous right now haha

BR

 

Honesly it really depends how DTG have developped it. However normally the dynamic brakes are used to manage the speed during the run, so normally you just need to know that the are applicate and the train is braking, so probably for this reason the train display just inform you about how many traction force the locos are appling and if the train start to brake or not. As the 4400 is a "modern" loco maybe it says just the "%" not how much power is applicate. However during the downhill is better to apply a huge force of the dynamic, if the train continue to not stop and the rollingstock push down the locos you need to "play" with the automatic brakes to help the locos to stabilize the train as that type of brakes are applied to the complete train. I don't know the correct word in english, but normally we call it "elastic effect" and you can see it expetially on very longer train.

 

Nice to see professional drivers answering! Do you have any thoughts on the clasp brake physics and my other feedback from the thread I made earlier: https://forums.dovetailgames.com/threads/several-bugs-and-incorrect-braking-physics.27117/
Maybe you are more used to trains with disc brakes where the brake force is nearly constant with regard to speed.

For everyone: It seems like people are judging the physics TSW2 on different platforms in here while Stujoy was talking about PS4.

How do you observe displays in the non-lead loco? Do simply walk in-between or is there a way to teleport?

 

[Ctrl][+] // teleport

EDIT

On PC

These numbers look inverted, but paradoxically they do not balance each other. As some have already noticed - the anomalies only affect AC loco.

UPDATE

As for mine, maybe it's even OK, maybe it's the power of suggestion or maybe something is up. I started to get dumbfounded in the conclusions of the TOO MANY trials, but always doubted if I use MU.

...PS

Something is wrong with AC in TSW 2. This is my impression.

 

I was hoping not to have to try and put a video up of this bug in action. I’m going to have to because some stuff filling up the thread is about other things that are not what the issue is. I knew this would happen. For various reasons I cannot make a video and get it up on this thread at the moment.

Some theory. The braking force that needs to prevent a train from accelerating is the same at any speed because it is only counteracting a proportion of the acceleration due to gravity. What does change with speed is the braking force the dynamic brakes create (with the lever set in one position), as the traction motors are generating the current that the system relies on. If there is enough braking force available within the system (at that lever position) to prevent a train from accelerating, when the train reaches the speed needed to create that braking force, the train will stop accelerating and maintain a steady speed. This is what indeed is happening on all other trains with dynamic brakes and you can verify this by seeing the same amps reading for the same train on the same grade at all different speeds (different settings of the brake are required but the braking force will be the same). You can see the amps slowly rise and then stop rising when the necessary braking force is generated. You only need to adjust the dynamic brake lever position if the grade changes.

This does not happen with the AC4400. You can be very close to having the correct braking force but the braking force shown will start to fall as the train gets faster. Put the brake in a higher notch and the same process will either happen again or you will get enough braking force and as the train slows down the braking force will start rising rapidly and the train will slow down at greater and greater rates of deceleration as the braking force rises, so you have to notch down again. If the train has slowed sufficiently, notching down will still result in far too much braking force and the train can slow to a crawl.

What is actually happening (the bug) is that the braking force is decreasing as the train gets faster (as if the traction motors are producing less current the faster they spin - impossible). At very low speeds an abnormally high amount of braking force is being generated (even in low notch positions of the lever) because of this inverted relationship between traction motor speed and braking force. At normal operating speeds the braking force is lower than it should be (even in the highest notch available) and continues to decrease as the train speed increases.

This is a process I went through to pin down exactly what is happening because I could not get the dynamic brakes to work properly under normal operations. The observations of the relationship of the wheel speed to braking force were not originally made during a normal run, even though it was happening and affects every run with two AC4400 as the locos.

All my tests have been done with the same train on the same grade, with only the speed and dynamic brake settings changing.

One thing is definite. On my PS4 the dynamic brakes on the AC4400 are behaving the way I described, which is not correct. I have thoroughly tested this issue and it is a bug.

 

I have read you thread and great job about it. I haven't check the thing about the weight of freight german train so i need to check better. About the physich i say that this is a game and it simulate very well a lot of thing that really happened in real life. However the number that you says are correct but in real life there are many variables to keep in mind, the max speed of the wagon, how is loaded the wagon, what kind of cargo you are traveling (exemple there is a lot of different between water - milk - gas - oil), how the train has been composite (exemple mixed freight train with the same destination used to set the hight weight wagon near the locomotive to have a better traction), than expetially on freght train every wagon has his story (exemple the same coal wagon could have a different performance and it could depends from the revision too) and you need to calculate if the track is dry or not and the gradient, if you put sand or not. I think that the most important thing that game doesn't calculate is the wind. Stop a 30 full loaded wagon in downgrade with a strong wind behind you could take 500m or more to stop plus the normal braking area of the train. Than it depends if the train is in curve or not, during a curve the actrition from the railway are a bit more stronger and it helps the train to stop. And there are a lot of things to say too. However thare are 2 important things to say. The game doesn't say how many space there is between the wagons (exemple if there is 5cm or 10cm of space. More space you have, more is easy to menage the train during a run but it increas the braking area because when the loco brakes the wagon number 40 still continue its run until it "touch" the wagon number 39 and this takes time and if you are running at 100kmh with 10cm of space with a train with 40 wagons, after a full train brake the wagon number 40 takes 3 or more seconds until it starts to brake. This is what i mean for "elastic effect". Now the second things is that in italy for exemple when the train is ready to depart we got a "train table" that says with weight, number and space, also the type of train (exemple in german O M or U) and the maximum permitted speed of the train (dependig from the slower wagon) and normally breaking area of the train from 120kmh to 0kmh. This is an indicator but during the way you need to "feel" the train and normally is better to menage speed to be safe. Is better take 5 minutes of delay that do a crash or a derailment. And another thing is that the game says a wrong think too. It says to not stress a lot of the train. It is incorrect, all components of every train are test until a breaking point that normally is much highter than the operating service so if you are not sure to stop the train before a signal, just the brake until the max to stop it, we do it in real life too if needed. Than another think that i really hate of the game is that sometimes the check point is too close to a red signal, normally is used to stop ~50 or more metres from the signal first to have a better view and second to be sure to stop the train before the signal expetially for freight train. So at the end, i think that the game physich is good as all mechanics a good balance between stressfully and funny. I know that it isn't perfect and it can be improved but it is good start to learn how works a train. Than you need to count that this is athe game and you play by standing in a place, so run at 80kmh when you approach a signal seems really fast but in real life is much slower the feels. Hope that this could help and no, in italy we have a lot of differnt locos and commuter to drive, so we have to know how works every type of brakes and how many we can stress it and we have locos that actually are in service that comes from 70s and 90s

 

I did my last PC trial and this is how it looks in summary:

2xSD40-2:
the indications in the cabins of both locomotives are correct
HUD OK
game physics as I imagined / like theory

2xAC4400CW:
trail-loco indications are INVERTED
HUD - shows the ZERO Klb value all the time and these dynamic bars seem to work, somehow
game physics - seems OK?

BUT: the ZERO on the HUD and inverted trail-loco values make me a bit worried - paradoxically, the train slows down, although UI says the second locomotive is pushing and the forces balance each other

The PC punch line: something is very wrong with the indications and UI, but the train seems to be slowing down as it should... maybe

I am no longer disturbing your cheerful and short arguments on...

I have asked so many times: don't buy a console!

 

Could you give me the number of service? Want to try it myself

 

I have a deep google-translate English but maybe it's called 'slack action'.

UPDATE

I suggest You use an editor (the fastest way) but it's the same everywhere

 

One thing I didn’t do and over the last few days I haven’t had the inclination to, is to try and get a train with a single AC4400 and a shorter rake of wagons up to the summit to test how a single loco behaves. I need to figure out a way to do that. Other than keeping an eye on this thread, I haven’t gone near an AC4400 since I first posted this issue, for fear of a nervous ‘dynamic’ breakdown. I’ll get round to it one day. With the likelihood of it being fixed so low, I don’t want to spend much time on it, for a while at least.

 

Which part of the route you normally test it? So i can set the editor

 

I think I've already done all the possible variants, with and without wagons, flat and downhill...
Throw maybe two naked ACs at Cumberland Yard - I did recently

 

Just trying now. 2 ac4400 with 50 coal wagon charged. 6800t.

 

I have no doubts about the problems with UI, MFD, but if you confirm - the train is behaving correctly - maybe I will fall asleep today...

UPDATE:

And I am quite sure, the problem appearing on PS4 described by stujoy is another story, much worse than daj Losie irrelevant bugs on PC

 

I would really recommend you to create a video if at all possible, it will make it easier for people on PS4 to see if they can reproduce the findings and also will give anyone all the data needed to come to their own conclusions.

I've already given my thoughts to the principles behind what should happen (which is the most I can do without seeing at what speeds force is reducing etc) so I won't clog up the thread more than to say that you *should* except the force to fall *at some point* (you cannot expect the force to be 100 klbf at 100mph etc) and I suspect that you may also see falling current due to back-EMF analogous effects for generators. I'm not saying this in disagreement of what you posted here, but rather as a general statement.

 

Ok just tied. First i can confirm that the train display shows the tractive effort and not how many power the locos are appling. Second with the configuration 2 ac4400 with 50 coal wagon fully charged 6800t after the sand patch tunnel to cumberland the downgrade reach up to 1.9%. Now at 40mph if you applicate N8 a full dynamic brake the train display and the game HUD will show ~ -50 klb of tractive effort. During the way the train continue to accellerate with a medium of 1.5% of downgrade and the tractive effort of the dynamic brakes will continue to decrease, not because i'm changing the power but because the coal wagons are pushing down the locomotive on the downhill. Simply you need to applicate the automatic brake too to help the locos. Simply the train is too heavy for just 2 locos for this reason you see that the dynamic brakes decrease, because, with an infinite downgrade at 1.5% the wagons will push the locomotive up to a breaking point of the dynamic brakes and the will show a -0 klb that means that at X velocity a N8 dynamic brake power simply doesn't apply a minimum ammount of tractive effort to try to stop the train, so the locos will works as they are set in neutral. The train works perfectly. Simply just need a lot of control to menage speed to decellerate the train or to keep your velocity. It is just too heavy. Normally in this case at least a banking loco is needed, or just another one in front.

 

Sounds logic. In my case ZERO was a permanent state even in no-wagons trials, but this is less important. Downgrade behavior seems to be OK for me too and the only weird THING in US-TSW-trains is an initial braking which should be 84 PSI not 80 or maybe not. Thank You for your effort PC 'bug' is a nuance, I think.

I read this thread more than once and I am sure I understand now, what stujoy is talking about.

 

Just to clarify i tried it on ps4 where was supposed to be bugged. I think that to make it more easy to understand the hud says how much resistance make the locos to the rest of wagons. For this reason i continue to say that the name dynamic brakes is incorrect and it create just confusion. For exemple in italy like in german it is called electric brakes and honestly we use it rarely at the full power

 

Well this issue made it onto the roadmap. Let's see what happens.

 

Yes, I’m happy about that because it is something that when the devs examine it they will see the issue, even if I have had difficulty in accurately describing what’s going on. In the meantime, I’ve been enjoying the SD40 on some runs.