Just wondering how the prototype MUing really works. I understand (I think) that the engines are linked together with the MU cables and the lead locomotive controls the other engines. What I am unsure of is exactly how each engine produces the correct tractive effort so they are working together and not against each other.
My understanding of how a modern diesel locomotive really works is basic at best. Big engine turns generator/altronator producing amps to drive traction motors turning the wheels…like I said basic.
My lack of knowledge in this subject is obvious when I wonder how engines of different hp ratings are mu’d together. Say at Dash 9 - 44CW with a GP38-2. If the lead engine is the -9 and the engineer selects a mid throttle range setting, how does that relate to the lower hp GP38-2? The -9 is 4400 hp and the GP38 is 2000 (I think). Quite a difference in hp. Would the -9 actually be pulling the GP38?
I ask because I am trying to speed match my engines on my pike (DCC). It has proved to be more difficult than I first thought it would be. It made me wonder how it was done in the real world. Seems the same laws of physics would exist.
Comparing matching engines on a layout to real ones is not the way to do it. The mass of the real thing eliminates the problems of models. As far as I can tell it is a virtual myth that disimilar speed engines will in any way harm one or the other. I have asked several times now for anyone who has had this problem to give the details and no one has ever said they had the problem. On the real thing the tonnage being pulled should equal the horserpower up front to do that. That being said the PRR did not mix engines until second generation units came out which made the problme a moot point.
Each locomotive generates whatever effort it can for the throttle raing. Since (theoretically) no one locomotive can pull the whole train, each locomotive contributes what it can.
In a tug of war, each person on a team is a different strength, but they all pull on the rope as hard as they can.
Some engines, such as Baldwin’s Sharks, could only be used with other Sharks. They had air-operated throttles…which wouldn’t work with EMD or Alco units.
That’s how things are controlled from the lead unit.
However, not all engines are MU-able. There are pneumatic MU systems too.
Firstly, as an example, some Fairbanks-Morse H16-44’s (including the New Haven’s first 10 from 1950 - 590-599) had the pneumatic throttle. Controlled by air, it could only MU with the other H16’s from that order - nothing else because nothing else on the roster had the air throttle.
As another example New Haven Alco and FM road diesels were MU-able. You could see a PA-1 with a DL-109 or a CPA24-5 with a DL-109 or a PA-1, etc…
These all had matching electric control jumpers - but, not all electric throttle units have the same jumpers - therefore a NH RS-1 could not MU with a RS-2 or RS-3.
Once things became more standard there were some strange consists. The NH 1956 road switcher order was all MU-able - so you could MU a RS-11, GP-9, and H16-44 (late model). And later after some FB, FA, and RS-3 units were rebuilt, you could see a FA, FB, RS-3, H16, RS11, GP9 consist!!!
It is not just the electric MU jumpers that are required to make things work. There are also additional air pipes to be connected up so that air tanks and the braking system are set up to be controlled from the desired unit. All pretty basic once you get the hang of it. I have actually seen a guy with an allegator clip on a piece of wire short out or earth the various pins in the MU plug to make the engine rev up and down.
Baldwin engines used a pneumatic system that was not compatible with the other manufacturers. So you would never see Baldwins mu;d with EMD, Alco, FM or Lima engines.
However a tug of war team is pulling on a common rope and the combined efforts would not normally be pulled down by lack of effort on behalf of any one participant. Unless they were just dead weight and stopping the rope from being moved.
Imagine if one person dug in their heels and put weight against their teams’ effort to pull. This would conteract some of the effort of others.
Mike: In rather broad terms, each notch of the throttle calls for a PERCENTAGE of available horsepower. In your example, if the engineer selected a mid range throttle notch that “called” for 50% of available power, the 4400 hp Dash 9 - 44CW would respond by producing 2200 hp and the 2000 hp GP38-2 would respond by producing 1000 hp. What the engineer DOES with the power is a whole 'nother story and that’s why the railroad is paying the engineer,
Once again you guys have made sense of my confusion. Thank you.
With much practice, I have been able to closely match most of my loco’s. I am using a digitrax zephyr will digitrax decoders. I have Athearn BB, Athearn RTR, Proto 1000, Proto 2000, and Walthers trainline loco’s. Still on the learning curve though. But that is what makes it fun.
For speed matching model locos with DCC, several good articles have been written in the various media. The following is a very brief description of one process.
The general procedure is first to set up each loco’s starting speed such that in speed step 1 the loco will start and keep moving at the slowest possible pace. The several locos do not necessarily need to exactly match in this speed step, but they do need to start movning and keep moving reliably. Next, pick a mid point speed which suits you – many people prefer a slow pace, so that we do not end up playing “slot trains”. Once one loco has a mid point speed (speed step 14) that you like, work to set up the other locos to that speed. Consist the locos together, but don’t couple them, and then run them together in speed step 14 and see if you can get them to pace each other. Be careful to match them in both directions (the better decoders can adjust for differences forward and backward). Finally, set the high end speed (speed step 28) to something a bit more than double the mid point, so that you have enough power to haul a load.
If the decoder has three point programming, you are almost done. If not, i.e. if you must program each speed step individually, then fill in the gaps between speed steps 1, 14, and 28 with a (more or less) straight line progression of values. Be very careful that each successive speed step is greater than the previous one, or you will get undesireable results.
Finally, recheck the locos together through all speed steps slowly, verifying that the MU operation is satisfying to you.
I know that you put 2 40-2’s on the nose pulling a Dash 9 and you will jerk it right off the line!Dash 9’s load slow when trailing then they might (depending on how well maintained they are) ram them 40’s ahead a bit on occasion .
Like posted prior thats why the engineer is getting paid the big bucks! To put that power to work for him not against him.When pulling a mixed consist off the pit one night and in its 5 mph limits, the 3 old units behind me never even got above idle as the Dash 9 was pulling them and the throttle changes so small that it never got back to them really.Once we got out into 20 mph tracks look out!we were backing and when I opened them up you could feel the slack go out as the rear units took off like race horses.
Also on this topic, not every loco consist has all motors working. In some case the horsepower per ton is too high with all working ( but if they are all old units and you want to get over the road faster you leave them online) so some are isolated or not even running. Having them up in with the other motors allows the engineer to actuate the brakes so the wheels will not slide when stopping.If you notice them in the consist without the big cable connecting them then thats probably the case. We do however make all air connections.
As far as MU’ing diesels together - here’s what’s hooked up. These days the locomotives have two sets of three hoses on each end of the locomotive in addition to a brake pipe hose for the train itself. The three hoses in each set provide the following functions - main reservoir, actuating air (bailing off), and apply and release (a+r).
The main reservoir hoses allow each locomotives air compressor and reservoir tanks to help supply the lead locomotive with all the air it needs to operate the air valves and keep the trainline charged. When a locomotive is set up in a trailing position its air brake functions as a lead locomotive are cut out and thus responds to air brake commands from the leading locomotive and basically functions like a box car - with the addition of being able to actuate or bail off an application of the locomotive brakes during a brake pipe reduction meant for the cars and not the locomotives in the consist. This function is provided to prevent excessive retarding forces on the head of the train when a brake application is being made. Since the locomotives are always heavier than the cars, a brake application on a locomotive will grab harder and faster than the brakes of a car. Bailing off allows a engineer to set the brakes on the train without the brakes of the locomotives applying.
The apply and release hose is basically the “straight air” for the locomotives brakes. This hose provides for INDEPENDENT control of the locomotive brakes - seperate from a brake pipe application. No air in this line means no brakes on the engines. Air pressure in this line acts on a relay valve (usually called the J-1 but there are several variations) that will then provide a corresponding pressure to the brake cylinders on its respective locomotive.
The act or acuating line as mentioned above annuls an application of the engine brakes during a brake pipe reduction thus allowing the engineer to keep the train stretched out during a braking application. Railr
One additional item of interest. If the lead unit is isolated it will provide no power to the train and becomes a control cab only. The engineer has control but not the noise of a diesel engine at his back. This is used if the train has enough power such as when moving extra power from one location the another and not all engines are needed on line.