I start with some assumptions: steady-state, no unit either in traction-motor slow-speed or overspeed risk, etc.
As noted in some detail over on MR, the MU systems need to be compatible, and to a lesser extent the gear ratios should not be wildly disparate (not so much because they 'want to go at different speeds' as because the horsepower in MU-commanded notch may not produce comparable TE). To an extent the speed with which locomotives load or unload affects their behavior in a consist: faster-loading ones may jostle their lazier neighbors (as has been remarked on both here and in Trains Magazine.
Sometimes the question arises 'how do the engines "know" which ones pull which share of the load'. (Also 'why does it always look like one of two steam locomotives doubleheading always look like it's doing more of the work -- and is this true for diesel-electrics?')
Think of it by starting this way: The rear unit has the entire consist's resistance pulling on its rear coupler. There is usually no way in Hades that unit alone could pull that ... let alone push a unit ahead of it too. The second unit forward, therefore, has at its coupler the full consist resistance (now including the mass of the trailing locomotive) LESS whatever that locomotive, running in commanded notch with corresponding excitation, is providing in wheel rim torque/dbhp to LESSEN the resistance. And so forth up to the lead unit.
Now, the unit controls don't make this calculation (although if they had strain gages on the drawbars and the right computer or PLC installation, they could). Instead their load regulators adjust excitation to keep the engines at constant rpm, which is separately adjusted with variable fuel. Fairly rapidly this equilibrates the load among the units so that no one of them is running at 'full gate' trying to pick up more than its share, and I believe this will be true even if its 'share' is numerically higher or lower than its neighbors (e.g. a DD35 sandwich)
JPS1 Yesterday I saw two Dash 9s and a SD40-2 pulling a freight train past my favorite train watching spot. What issues, if any, arise when locomotives from different manufacturers operate together?
In this case, absolutely none! These units don't know who made the one ahead or behind.
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BigJim JPS1 Yesterday I saw two Dash 9s and a SD40-2 pulling a freight train past my favorite train watching spot. What issues, if any, arise when locomotives from different manufacturers operate together? In this case, absolutely none! These units don't know who made the one ahead or behind.
The volts and amps of each engine have no idea of the volts and amps of any of the other engines in the consist - each locomotive is working to its own maximum capability for the throttle notch that the engineer has selected.
Never too old to have a happy childhood!
And the resultant speed up the grade or acceleration results from their combined tractive effort and horsepower with the division not necesarily proportional to the different rated tractive efforts and horsepowers.
(Only if wheel sizes and gear ratios are the same, then possibly proportional depending on governor settings and contorl system timings)
BaltACDThe volts and amps of each engine have no idea of the volts and amps of any of the other engines in the consist - each locomotive is working to its own maximum capability for the throttle notch that the engineer has selected.
Don't some of the newer engines have that smart consisting or EM stuff, and do know what the other engines are doing? I know when I ran some of the GEVOs or ACes, I beleive they had displays that showed what other engines were doing, if they also had compatible software. It's been a few years since I've had that high tech stuff.
Jeff?
The opinions expressed here represent my own and not those of my employer, any other railroad, company, or person.
zugmannDon't some of the newer engines have that smart consisting or EM stuff, and do know what the other engines are doing?
The point is that most of that stuff is also handled between computers, or communication via the 'back office', not directly meant to be manipulated by the people, or person, or occasional flying 'superconductor' or riding supervisor when autonomous trains set in. My guess is that your actual control over much of that is limited by the interface in the first place, and by access permissions and 'not being distracted by electronics while maintaining vigilance' (or some other mealymouthed excuse) should you try making informed use of the dataflow and controls.
Of course in an emergency it would be of great use to be able to reach out, diagnose, and develop workarounds for failing units you need...
OvermodMy guess is that your actual control over much of that is limited by the interface in the first place, and by access permissions and 'not being distracted by electronics while maintaining vigilance (or some other mealymouthed excuse) should you try making informed use of the dataflow and controls.
If you only knew at times...
zugmannIf you only knew at times...
Not that I officially know anything of the kind, of course, or leave any back doors or stuff open after, well, you know, someone spills the beans too much not to notice. Heaven forbid.
zugmann Overmod My guess is that your actual control over much of that is limited by the interface in the first place, and by access permissions and 'not being distracted by electronics while maintaining vigilance (or some other mealymouthed excuse) should you try making informed use of the dataflow and controls. If you only knew at times...
Overmod My guess is that your actual control over much of that is limited by the interface in the first place, and by access permissions and 'not being distracted by electronics while maintaining vigilance (or some other mealymouthed excuse) should you try making informed use of the dataflow and controls.
Here's an example.
We used to be told to use Trip Optimizer as much as possible (CN doesn't use any of the other systems), and WiTronix would 'phone home' if we were not using it. When in Trip Op we are exempt from obeying throttle restrictions, as the program is supposed to be smart enough to calculate how to save the most fuel.
Eventually someone figured out that if you opened the Trip Op screen and "intialized" it, no alarms would be generated. But you would still be free to manually control the throttle, without being hindered by those pesky throttle restrictions.
Eventually the Company figured out what was going on, and now we are told not to use Trip Op, and obey the throttle restrictions religiously.
Greetings from Alberta
-an Articulate Malcontent
SD70Dude zugmann Overmod My guess is that your actual control over much of that is limited by the interface in the first place, and by access permissions and 'not being distracted by electronics while maintaining vigilance (or some other mealymouthed excuse) should you try making informed use of the dataflow and controls. If you only knew at times... Here's an example. We used to be told to use Trip Optimizer as much as possible (CN doesn't use any of the other systems), and WiTronix would 'phone home' if we were not using it. When in Trip Op we are exempt from obeying throttle restrictions, as the program is supposed to be smart enough to calculate how to save the most fuel. Eventually someone figured out that if you opened the Trip Op screen and "intialized" it, no alarms would be generated. But you would still be free to manually control the throttle, without being hindered by those pesky throttle restrictions. Eventually the Company figured out what was going on, and now we are told not to use Trip Op, and obey the throttle restrictions religiously.
For us, they've always known if you used the EMS or not. Even if you logged in but ran manual, they knew it. It's why at the end of the trip you had to give feedback as to why you didn't use it when it was available.
Jeff
zugmann BaltACD The volts and amps of each engine have no idea of the volts and amps of any of the other engines in the consist - each locomotive is working to its own maximum capability for the throttle notch that the engineer has selected. Don't some of the newer engines have that smart consisting or EM stuff, and do know what the other engines are doing? I know when I ran some of the GEVOs or ACes, I beleive they had displays that showed what other engines were doing, if they also had compatible software. It's been a few years since I've had that high tech stuff. Jeff?
BaltACD The volts and amps of each engine have no idea of the volts and amps of any of the other engines in the consist - each locomotive is working to its own maximum capability for the throttle notch that the engineer has selected.
Those engines equipped have a consist monitor. There's a limit to how many trailing units it will display, but all you see is tractive/brake effort. At least you know if the trailing units are working. I've had too many engines with smart start/stop that won't restart when needed and won't ring an alarm bell that there's a problem.
There was an EMS (Smart Consist) that showed what the trailing units (up to 2) were doing, but SC was deciding how each engine produced power. No one, except maybe bean counters who don't know much about how things really work in the real world, liked it. Even managers, except those who drowned in the kool-aid and thought they were destined to high management positions, who had to enforce it's use thought it was a big waste all the way around.
Modern locomotives all use the same connections and are full interoperable. Some older units (pre-1960s) had slightly different MU cable pin arrangments and not all the features would work on trailing units when you had mixed consists (NDG stated on several occasions that EMD and FM units had different dynamic brake control systems, and the DB would not work on trailing units when the two were coupled together).
Air brakes are another story, some older units with 6 or 14 (and some 26) "one pipe" systems could not lead units with 24 (and most 26) "two pipe" systems, as there would be no way to bail off the trailing units. Someone eventually realized that in this situation you could connect one of the lead unit's MU sander air hoses to the bail off hose on the trailing unit, and then turn the applicable sander switch on whenever you wanted to bail off.
Most Baldwin diesels had a air-controlled throttle that was not compatible with units from other builders, though some were later retrofitted to make them compatible.
Specialized features like Distributed Power and Pacesetter (automatic slow speed control) still have their quirks and surprises. The latest versions of DP (since about 2015) seem to have resolved most of the compatibility issues, but I've seen a few cases where we couldn't get older units from different railroads to link to each other, and of course the older Locotrol I and II systems are not compatible with modern DP.
Pacesetter seems to have been standardized since about 2005 (GEVO and SD70M-2/ACe), but anything older than that can have any one of several systems, and not all of them will work together. With a mixed consist there was no way to know in advance exactly how each trailing unit would react to the leader. Some would trail properly behind units they could not lead, some would trail in straight throttle, others would rev up and not load, or not react at all.
Darn duplicate postings.
If my memory is correct... The Atlanta and StAndrews Bay RR ( Bay line ) had an old Alcoa Road Switcher model unknown on display in Panama City, Fl. Opened the MU cable connector and it only had about 19 (?) pins. That was a surprize to me.
I suspect the Alco was old enough to use an air throttle, thus needing fewer MU connections.
I think this is an older style of GE multiple-unit control; units up to S4 had it, which I think is long past the time of air throttle control on 539 Alcos. I can't remember the date of adoption of AAR S-512, but I suspect the GE system (derived from electric practice, iirc) predates it.
blue streak 1 If my memory is correct... The Atlanta and StAndrews Bay RR ( Bay line ) had an old Alcoa Road Switcher model unknown on display in Panama City, Fl. Opened the MU cable connector and it only had about 19 (?) pins. That was a surprize to me.
This is a related question. I think!
Yesterday I saw three BNSF Dash-9s pulling a train past my next best train watching spot. The first locomotive was facing forward, but the two trailing locomotives were facing rearward. Or for the uninformed like me, the front locomotive was going forward and the two other locomotives were backing up. (Chuckles will be held to a minimum please.)
When the locomotives are positioned like so, do the ones that appear to be backing up have to be set manually before the train departs or is the process automatically set from the lead locomotive?
JPS1This is a related question. I think! Yesterday I saw three BNSF Dash-9s pulling a train past my next best train watching spot. The first locomotive was facing forward, but the two trailing locomotives were facing rearward. Or for the uninformed like me, the front locomotive was going forward and the two other locomotives were backing up. (Chuckles will be held to a minimum please.) When the locomotives are positioned like so, do the ones that appear to be backing up have to be set manually before the train departs or is the process automatically set from the lead locomotive?
Trailing locomotives, no matter the direction their cabs are facing, are set up as 'trailing' locomotives. As such their electrical and power circuits are controlled by the control inputs that the designated 'lead' locomotive makes.
When the Engineer places the reverser in Forward and then advances the throttle to notch 4 - all locomotive that have been configured as 'TRAIL' will do the same. The 27 pin MU cable that is connected between the units transfer all the electrical controls, the 'small' air hoses on either side of the coupler when coupled between the units pass all the pneumatic contol inputs.
When you start talking DPU - Jeffhergert would be the local expert.
But how do the rear-facing units know that the lead unit's "Forward" is "Reverse" to them?
Lithonia Operator But how do the rear-facing units know that the lead unit's "Forward" is "Reverse" to them?
It is hardwired in.
I believe that the forward and reverse pins are in opposite places on the MU plugs at the front and rear of the locomotive.
When setting up DP the direction in relation to the lead consist must be entered manually, you can choose "same" or "opposite". If you get it wrong the remote will work against the lead consist (this has happened a few times over the years).
Lithonia OperatorBut how do the rear-facing units know that the lead unit's "Forward" is "Reverse" to them?
In DPU each trailing consist has to be set for direction at the unit containing the radio receiver but the other locomotives in that consist are 'automatically' cable MUed.
Recently I reviewed the GE 29-notch MU on the PRR E44s when participating in the thread containing the 1966 DDR proposal. There the issue of 'handedness' was addressed by having MU receptacles both sides but keeping cables between units 'all to the same side'.
When set up in Trail - units have no idea what is ahead or back - they are dependent on the designated Lead locomotive to defined direction of movement to the Trail units by the electrical and pneumatic control signals that are sent from Leader to Trail units via the MU and pneumatic connections. When set in Trail, locomotives cede their 'mind' to the Leader.
BaltACDthey are dependent on the designated Lead locomotive to defined direction of movement to the Trail units by the electrical and pneumatic control signals that are sent from Leader to Trail units via the MU and pneumatic connections.
The two control wires for forward and reverse are reveresed at the rear of the locomotive and in the MU cable, the are not reversed at the front of the locomotive.
BigJimThere are no pneumatic control signals between the locomotives that pertain to which direction the units are travelling.
Naturally on locomotives with pneumatic throttles, there would be air connections. There are very few of these still operating. I don't know if there are two locomotives so equipped still running in MU ... perhaps on SMS?
OvermodMore precisely, the hose connections made when units are MUed pertain to 'control' over several functions of the air-brake system, including charging, main-reservoir equalization, and independent-brake connection between units. (These multiple connections were seen on electric locomotives like GG1s, not just diesel-electrics.)
MR, actuating, apply & release.
zugmannMR, actuating, apply & release.
BigJim BaltACD they are dependent on the designated Lead locomotive to defined direction of movement to the Trail units by the electrical and pneumatic control signals that are sent from Leader to Trail units via the MU and pneumatic connections. There are no pneumatic control signals between the locomotives that pertain to which direction the units are travelling.
BaltACD they are dependent on the designated Lead locomotive to defined direction of movement to the Trail units by the electrical and pneumatic control signals that are sent from Leader to Trail units via the MU and pneumatic connections.
There are no pneumatic control signals between the locomotives that pertain to which direction the units are travelling.
They pertain to the controlled ability to stop among all the units of the engine consist so coupled.
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