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Cruise control Rate Topic: -----

#51 User is offline   Weter 

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Posted 17 July 2021 - 03:20 AM

And speaking more simply, imagine a single-speed bicycle, four-geared car, and advanced automatic transmission-equipped vehicle.
The motor has quite narrow ability to change its torque according to speed (which is called characteristic). The more suitable for traction purpose is characteristic, described by hyperbola law, which allows to direct all the power of motor to tractive force at zero speed, or gain high speeds, trading the most of tractive effort, as most of power will de used to increase and maintain motor's speed of rotation. This is exactly, what is needed for transport application, as it allows to bring heavy loads to movement, to accelerate efficiently, as friction resistance decreases after movement begins, and, what is essential, to automatically maintain the balance of constant power, converting the part of it to speed, and the rest part to force, with ratio, depending on current conditions (uphill-downhill, wind direction, etc.)
So special constructions of motors and generators were chosen, whose characteristic looks like hyperbola, for use in transport applications.
The only problem is in very narrow ranges of this ability, for given motor. So it was extended by changing of gear ratio in mechanic transmissions, or electric supply characteristics in case of electric transmission, depending on actual vehicle's speed. The notched controllers did that by "switching from curve to curve" and modern ones, which are able to compute and apply variable characteristics of feeding voltage, allow to have the single synthesized curve for whole speed range.

#52 User is offline   Weter 

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Posted 17 July 2021 - 03:44 AM

http://ceae.ru/files/pic_6_25.jpg
Curves for some of 15 controller's notch at diesel locomotive.
And whole averaged traction curve of M62
https://sinref.ru/000_uchebniki/05300_transport_jd_teplovozi/160_teplovoz_m62_1972/000/004.jpg
You can see "forbidden" area at the upper-left corner and automatic-transition of two-step field-weakening in the middle.
http://ok-t.ru/studopedia/baza19/1477720447717.files/image021.jpg
Here is curves set for freight DC-electric loco for you to compare.
As earlier, there are limitations, tied with prevention of engines over-heat, spoiled commutation, wheel slip beginning.
Heavier the loco-upper the adhesion limitations. More the voltage-higher the speed. So we can see series (С), mixed (СП) and parallel (П) motors arrangement-corresponding curve sub-sets.
The article, explaining things in details

#53 User is offline   steamer_ctn 

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Posted 17 July 2021 - 02:54 PM

 Csantucci, on 16 July 2021 - 11:25 PM, said:

it's not so. If you look at the code for the InterpolatorDiesel2D or perform a test, you will see that for speed and force all units of measure generally accepted by OR can be used in these curves, and among them there are kmh and kN.

Thanks for that. After reviewing the code, I agree with you that appropriate UoM can be assigned to the table values.

However that raises another potential issue that I would appreciate your input on to confirm my interpretation of the code after reviewing it.

Firstly on pg 144 of the latest manual it states, "The ORTSMaxTractiveForceCurves are formed by blocks of pairs of parameters representing speed in metres per second and tractive force in Newtons". In the code example above this statement it also shows dimensionless (ie no UoM) values, and thus I suspect most people have interpreted this to mean that the dimensionless values are in metres per second and Newtons.

Secondly when reading this table OR uses the SpeedDefaultMPH as the STFReader constraint for reading the speed column. This constraint appears to assume that for dimensionless values that the user has entered the table values in mph, and hence then internally multiplies it by 0.44704 to convert it to the internal standard of m/s. Hence all users who have used dimensionless values in the ENG file on the understanding (from the manual) that they were supposed to be in m/s have introduced an error into their setups. This error will result in a reduction in force at the desired speed.

So at the moment my thoughts would be that it should use the Speed STFReader constraint instead.

I haven't had time to test this yet, and my comments are purely based upon a quick code review.

Can you see any problems with my interpretation? If you agree I will run some tests and look to a solution.

Are you aware of any reason why SpeedDefaultMPH has been used instead of Speed as the STFReader constraint?

#54 User is offline   R H Steele 

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Posted 17 July 2021 - 03:07 PM

I for one, read the manual very carefully, and posed some questions...the result was that I interpreted the ORTSMaxTractiveCurves to use UoM of m/s and newtons...furthermore, that these UoM need not be expressed in the table and were the default that OR uses...a bug if this is not the case. It might explain some discussions in the threads ( and behavior I've witnessed ) of trains when using the curve set.
Very Interesting, thanks for spotting this Peter .. certainly deserves further examination...hope it is easily corrected if true...we'll see.

...as an aside, referring to all other tables used in the OR diesel engine definition I have not used UoM, relying upon the interpretation that OR has been coded to use the defaults for that table.

#55 User is offline   Csantucci 

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Posted 18 July 2021 - 12:13 AM

Hi Peter,
when I checked the code yesterday, I was surprised to see that it assumes as speed default mph, as you also spotted; I guess that this has been done following the MSTS approach, where the speeds for the dynamic brake block are all assumed to be expressed in mph as default.
Therefore what the manual states seems to be wrong and should be corrected. It's too late now to correct the defaults for that tables in the code, because there are already many locomotives that use such tables.

#56 User is offline   Weter 

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Posted 18 July 2021 - 12:21 AM

Oops.
Then, only manual with correct instructions will help everybody.

#57 User is offline   steamer_ctn 

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Posted 18 July 2021 - 12:42 AM

Hi Carlo,

 Csantucci, on 18 July 2021 - 12:13 AM, said:

when I checked the code yesterday, I was surprised to see that it assumes as speed default mph, as you also spotted; I guess that this has been done following the MSTS approach, where the speeds for the dynamic brake block are all assumed to be expressed in mph as default.
Therefore what the manual states seems to be wrong and should be corrected. It's too late now to correct the defaults for that tables in the code, because there are already many locomotives that use such tables.

Thanks for the confirmation.

I will start a new thread in the near future with a view to correcting the issue.

#58 User is offline   Laci1959 

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Posted 18 July 2021 - 12:51 AM

 Csantucci, on 18 July 2021 - 12:13 AM, said:

Hi Peter,
when I checked the code yesterday, I was surprised to see that it assumes as speed default mph, as you also spotted; I guess that this has been done following the MSTS approach, where the speeds for the dynamic brake block are all assumed to be expressed in mph as default.
Therefore what the manual states seems to be wrong and should be corrected. It's too late now to correct the defaults for that tables in the code, because there are already many locomotives that use such tables.

Hello.
The European documentation always gives km / h and kN. The current format saves spreadsheets from unnecessary conversions. Creating a spreadsheet in kilometers is not easy anyway.

Regards Laci 1959

#59 User is offline   Weter 

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Posted 18 July 2021 - 01:14 AM

Or we should base on SI UoM for everything.

#60 User is offline   steamer_ctn 

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Posted 18 July 2021 - 01:45 AM

 Weter, on 18 July 2021 - 12:21 AM, said:

Oops.
Then, only manual with correct instructions will help everybody.

Who do you have in mind to provide correct instructions?

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