Trains go too fast

arum

USLW Creator/ TCS
I have put up 15 mph invisible speed limit signs but the locos still go about 20 at some points. Then the train slows and then go back up to 20 or higher. This is when its under AI control, and I cannot find out what is causing it. There is a long single straight section or track where the engine will run at the speed limit, but it seems that when the train crosses junctions it will go faster then the speed limit even if there is a limit sign right on the other side of the junction. I'm sorry if this isn't clear, it's late at night here and I'm tired from trying to get this to work...
 
Very well described: You are not the only one with this problem. I know of several members complaining of this. It has been posted but so far no solutions. Anybody... with an answer?
 
AI (which is, in effect, DCC control) has limitations when controlling train speeds - generally, though not in all cases, a locomotive advances to the speed limit much more quickly than it should (or, could, in the 'real' world) and grinds to something of a shuddering halt in a distance much less than it would really be able to.

I have found that many locomotives under AI control tend to 'surge' when observing speed limits of 40kph or less - accelerating and then deaccelerating between (say) 45kph and 25kph (more or less). Some content creators have managed to devise engine models with physics which do not demonstrate these characteristics, but by no means the majority.

If using AI alone then I do not think there is a fix. Most content creators seem to concentrate on producing models that respond best to direct cab control. which is appropriate, when you think about it, because this is how locomotives are really driven.

I have overcome the surging only by increasing the line limit so as to obviate the characteristic.
 
I have found it better to use more speed signs and bring the train down slowly so the jump is not so great,
 
The problem is that the train is not observing the 15 mph speed limit, but goin as fast as it wants. I think it has someting to do with the junctions. On a straight (non junction) piece of track it will follow the speed limit, but as soon as it crosses a junction its speed will go up past 15 mph.
 
Being fairly new I'm going to go out on a limb about this, but here goes:

I would imagine the trains (under AI control) use a control algorithm to control the speeds, similar to proportional-integral-derivative (PID) process control. This allows a process variable to be controlled to an exact setpoint value.

If you change the setpoint, the algorithm will determine what needs to be done to attain the new setpoint. If you've just entered a 60 limit from a 15 limit, the algorithm will open the throttle wide until it starts getting close to 60mph and then notch it down again. However, it is very likely to overshoot and for the speed to go over 60 before settling back to it.

I also don't know if the constants within the algorithm change for different locomotives or train weights. You might expect the proportional band to be wider for a more powerful locomotive or for the derivative term to be greater for a heavier train. I don't know if TRS2006 takes account of this.

It's possible if you are taking a train through a series of varying speed limits you are changing the setpoint speed more rapidly than the train can react to it, thus confusing the response from the algorithm. This might result in unexpected results, especially if the PID constants are not correct to start with.

warrior
 
That seems like a good explanation except that the speed limit if 15 constantly, so there should be no change in the speed at all. (in the sense of 15 to 60 and such)
 
I'd just like to say tHat I have tested out different things, such as changing the switchstands, and my trains continue to go too fast. I have a constant speed limit of 15 mph over the entire route, with it as low as 10 in some areas. Out of the various tests, the speed go over 15 the highest when it is coming close to, crossing, and just after a junction. Soon after crossing the junction the speed will go back down to the limit....until another junction comes. I believe my signalling is good but I'm stumped on how to remedy this problem with the speeds.

Just to recap,my trains go over the speed limit, a constant 15 mph, whenever it is crossing a junction, and will then return to proper speed. Thanks very much for any help!
 
What happens if you manually set the junction against the AI train, so the AI driver gets hold of the junction and switches it as it approaches? Do you still get the same problem?

warrior
 
Yes, the problem persists doing what you said. I'll just live with it for now. Nothing seems to make it change.
 
wow warrior that look like advanced stuff you got there.
yea most likely thats what happining but im not entirely sure myself.....
 
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