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Eng Files for USA diesels Looking for data... Rate Topic: -----

#21 User is offline   Weter 

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Posted 15 August 2021 - 02:15 AM

And in case of starting from uphill?

#22 User is offline   steamer_ctn 

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Posted 15 August 2021 - 04:24 PM

View PostR H Steele, on 14 August 2021 - 10:12 PM, said:

That's interesting...never thought about it in that way. How could that assumption be tested, or perhaps someone familiar with the code would know?

My understanding is that in the real world starting TE (MaxForce) is not capped as such, it could reach a much higher value. The MaxForce value is the typical "design" value when wheel slip may start to occur, and hence in practical terms the locomotive cannot produce a greater value of starting tractive force (otherwise wheels start slipping, and the locomotive won't move).

OR caps the MaxForce to the value set by the user, however the performance of the locomotive is also dependent upon the adhesion of the locomotive. Hence if the MaxForce exceeds the Adhesive force (related to adhesion) then the locomotive will not be able to exert its full starting TE.

#23 User is offline   R H Steele 

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Posted 19 August 2021 - 02:10 PM

View PostTraindude, on 14 August 2021 - 05:06 PM, said:

Then I looked at the .inc files and it turns out the ORTSMaxTractiveForceCurves tables' minimum speed is only around 7-10 MPH. Thus it became necessary for me to add additional curve points for 5 MPH (2.24 m/s) and 2.5 MPH (1.12 m/s) to make starting easier.


The minimum speed for the ORTSMaxTractiveForceCurves I've constructed is set when Notch8 attains maximum Tractive Effort. Other power settings lower than 100% will also attain this MaxTE, however, it will be at a lower speed. The lowest speed of each notch is zero m/s, Hopefully the OR interpolator will generate the correct tractive effort for each notch for speeds that fall below the minimum speed down to zero.

Two possible problems: Does the OR interpolator work properly in this instance? (I'm assuming – yes ) ...and...That I've capped the maximum for each notch...I'm not entirely positive that presents no problems. Especially since steamer_ctn in post#22 provides this information:

View Poststeamer_ctn, on 15 August 2021 - 04:24 PM, said:

My understanding is that in the real world starting TE (MaxForce) is not capped as such, it could reach a much higher value. The MaxForce value is the typical "design" value when wheel slip may start to occur, and hence in practical terms the locomotive cannot produce a greater value of starting tractive force (otherwise wheels start slipping, and the locomotive won't move).

OR caps the MaxForce to the value set by the user, however the performance of the locomotive is also dependent upon the adhesion of the locomotive. Hence if the MaxForce exceeds the Adhesive force (related to adhesion) then the locomotive will not be able to exert its full starting TE.


I'm working on refining the curves and this is something I'm going to work on. Additional speed points below the minimum already given in the curves may be necessary ( especially if the OR interpolator does not apply to this case )...knowing more about the interaction between MaxForce and Adhesive Force will be helpful. Sources –- anyone?

View PostTraindude, on 14 August 2021 - 05:06 PM, said:

To make the calculation of the theoretical TE easier, I made an OpenOffice Calc spreadsheet. By simply entering the horsepower, speed and throttle notches, a TE table is automatically generated...


I'm assuming the spreadsheet example was for an EMD E8? If so, that brings up another question I have. The E8 is listed as 2250hp –- power delivered to traction motors. My understanding is that rail horsepower is used to calculate tractive effort.

One item that would help me is to have an example of the “light consist” that gave you problems starting --- locomotive/s, number of cars, and total car mass, grade...that would help me test. The starting problems could be from other factors that neither you or I have thought of. I would like to try and duplicate your experience so I could refine my testing.


#24 User is offline   pschlik 

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Posted 19 August 2021 - 02:49 PM

For reference, most freight locomotives can dramatically exceed their adhesion rating. I don't know how locomotive companies ever figured out exactly how much tractive effort is possible where adhesion is not a problem (since it basically always is a problem), but they know stuff like a GP39-2 could theoretically pull off 87,000 pounds of tractive effort despite the fact that you'd never get more than about 55,000 pounds out. This 87,000 pounds is the max you could get out of any 4 axle locomotive with the D77 motors (GP15, GP38, GP40, etc) as that is what occurs at the 1,500 amp limit of the motors.

https://i.imgur.com/BuoLkFk.png


The habit many OpenRails creators have of limiting the tractive effort curves to not exceed the adhesion rating of a locomotive is outright wrong and I abandoned that practice in my physics set months ago. I'm pretty sure this practice came about as a crude way to reduce wheel slip (since, ya know, wheel slip protection isn't simulated and every time it's proposed there are just excuses and workarounds proposed instead of actually solving the problem), which is fair enough, but we shouldn't go telling ourselves this is realistic.

#25 User is offline   engmod 

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Posted 19 August 2021 - 03:49 PM

View Poststeamer_ctn, on 15 August 2021 - 04:24 PM, said:

My understanding is that in the real world starting TE (MaxForce) is not capped as such, it could reach a much higher value. The MaxForce value is the typical "design" value when wheel slip may start to occur, and hence in practical terms the locomotive cannot produce a greater value of starting tractive force (otherwise wheels start slipping, and the locomotive won't move).


This is true for the first generation diesels as they had no control of current.

The second generation with electronic controls ( sd40-2 and later ) did limit the starting current. I don't know when GE started electronic control.

#26 User is offline   Traindude 

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Posted 21 August 2021 - 12:10 AM

View PostR H Steele, on 19 August 2021 - 02:10 PM, said:



I'm assuming the spreadsheet example was for an EMD E8? If so, that brings up another question I have. The E8 is listed as 2250hp –- power delivered to traction motors. My understanding is that rail horsepower is used to calculate tractive effort.


I am using the "rated" 2250hp as a basis for my spreadsheet. So the formula for the E8, as described in the specification card would be:

(308*(2250hp*(throttle notch/8)))/mph

View PostR H Steele, on 19 August 2021 - 02:10 PM, said:

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One item that would help me is to have an example of the “light consist” that gave you problems starting --- locomotive/s, number of cars, and total car mass, grade...that would help me test. The starting problems could be from other factors that neither you or I have thought of. I would like to try and duplicate your experience so I could refine my testing.


In this case, I was using first a single "A" unit (148.4205 short tons), and then an "A-B" set (292.7076 short tons combined) of Richard Cowen's repaint kits and 5 of midneguy's Burlington heavyweight passenger cars--one RPO (69.9 short tons) and 4 coaches (76.2 short tons each). The total tonnage of the passenger cars is therefore 374.7 short tons. All .eng and .wag files were modified from their original versions for experimental purposes. This is all on a flat grade on CTN's test route, specifically the "Level Path Over Water Trough" path (SW corner to NE Corner).

Without my modifications of the added low speed steps, the train would not move when I moved the throttle from idle to notch 1. It was only when I advanced the throttle from notch 1 to notch 2 did the consist start to move--and that's at the start of the run!

My modified .eng and .wag files, as well as the .con files, are available via PM.

#27 User is offline   darwins 

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Posted 21 August 2021 - 05:53 AM

I am noticing a difference here between the US throttle and the older type of British throttle. With the British throttle moving from OFF to ON or 0 to 1 is not increasing the rpm very much if at all. It gives power with the engine running at idle speed or just above - which is usually just enough to move the loco up to 5 mph or so - ideal for moving around a yard or shed or gently buffering up to a train. On the other hand the US throttle is giving 1/8 full power on the first notch. For a modern freight loco with a diesel engine of 3000bhp that delivers more power to the traction motors than one our shunting locos (switchers) has as total installed horsepower!! How do you manage to carry out light engine movements in yards, shunt wagons or couple up to trains without crashing in to them?

#28 User is offline   pschlik 

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Posted 21 August 2021 - 11:28 AM

View Postdarwins, on 21 August 2021 - 05:53 AM, said:

On the other hand the US throttle is giving 1/8 full power on the first notch.


And there's another assumption everyone seems to make that's outright wrong. Notch 1 is not 1/8th power, notch 2 isn't 2/8th power, etc. It's not directly proportional by any means, for the exact reason that applying 12.5% power in notch 1 would be far more than anyone would want for a light engine.

In general, the power grows under-proportional per notch...climbing very little at lower notches but increasing significantly in higher notches, while the starting tractive effort (ie: the motor current limit) increases over-proportional with each notch...climbing most in low notches but leveling off in high notches.

#29 User is offline   darwins 

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Posted 21 August 2021 - 11:39 AM

Quote

And there's another assumption everyone seems to make that's outright wrong. Notch 1 is not 1/8th power, notch 2 isn't 2/8th power, etc. It's not directly proportional by any means, for the exact reason that applying 12.5% power in notch 1 would be far more than anyone would want for a light engine.


I am very relieved to hear that.

Could you give me some idea of the approximate % of full power that the 8 US throttle notches might correspond to?

#30 User is offline   pschlik 

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Posted 21 August 2021 - 04:54 PM

View Postdarwins, on 21 August 2021 - 11:39 AM, said:

I am very relieved to hear that.

Could you give me some idea of the approximate % of full power that the 8 US throttle notches might correspond to?


Varies a lot per engine, but for something modern you might be looking at like 6% power in notch 1, 13% in notch 2, 28% in 3, 39% for 4, 52% in 5 (note how we didn't even reach half power until after notch 4), 69% in notch 6, and 84% in notch 7. Older locomotives may have the power curve even more biased towards the higher notches, and this curve would be pretty relaxed in comparison. The point being, there is no one size fits all for notch-by-notch power output.

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