Thanks for the prompt reply! And please don't think I'm arguing with you...I'm simply revealing my ignorance. I think I'm following what you've said but here's where the comparison breaks down for me: in your "folks pulling on a rope" scenario, all of those feet have a tremendous about of variety in how they are interacting with the ground -- some have traction, some are doing the stutter-step, some are maybe even scuffing and slipping. With multiple locos, the analogous contact points are the wheels against the rails. If I understand your example, then there would need to be some "give" at the wheel/rail interface...and the ones that were producing slightly less force than the strongest ones would be able to slip there. Let me reduce my mental image to the basics: if one electric motor, tied to an axle sitting on a rail, is running at 100 rpm and another electric motor, tied to another axle sitting on the same rails (and all joined together at the coupling) is running at 99 rpm....somewhere, sumthin's gotta give. So what am I still missing?
In the case of supplemental diesels with steam excursions, a standard hostler control is mounted in the steam locomotive to control the diesels. This control has no linkage of any sort with the throttle of the steam locomotive.
First: DPool !
Many of the Steam engines that power the Railfan Train trips; seem to have noted at some point in their narrative history's the fact that in the cab of the [steam] locomotive the owing entity has provided a 'control stand' to allow operation of a diesel engine accompanying the steam power. [ MU connections for throttle and other critical features provided to make that steam/diesel combination system work?].
I am not exactly sure how the 'hybrid mechanics' of such a system functions; but they seem to be able to operate very well ? Note: the UPRR's steam heritage fleet operates successfully, many miles, with accompanying diesel power. As do many of the other heavier steam engines,(nee: SP4449, for one other operating example.
aboard sir! We have fun here and sure learn from each other!
Getting to your question, and mind you I'm not an electrical or mechanical engineer, or a professional railroader, and make no pretense at being any of the above, it sounds like what your referring to is called "multiple-unit control."
This is fairly old technology, it goes back to the turn of the 20th Century when Frank Sprague developed it for control of multiple unit lashups of trolley cars. One throttle or controller would exercise control of all powered units.
It's now applied to multiple diesel unit lashups, although I'm sure it's a lot more sophisticated now than it was back in Spragues time.
The only difficulty encountered now, from what I've learned from various topics here in the Forum, is when units of different manufacture such as GE or EMD are part of the lashup. I've read that the GE units don't "load", that is power up and move, as fast as the EMD units do. There's a bit of a lag. Once the GE's are up to power there's no problem.
Anyway, multiple unit control capability is one of the things that attracted railroads to diesel power. Instead of multiple steam engines with multiple crews any amount of diesels could be coupled together with one engineer controlling the lot. It works, and works well.
If anyone wants to correct me on this go right ahead, I'm not proud.
The short answer is NO. Each loco is its own power unit that moves freely on its own and it doesn't care what the others are doing. Think of a load that you want to drag across the ground. Add a long rope. One muscle builder guy can't pull the load. Add a normal guy and they still can't pull the load. Add a teenager and the load starts to move, slowly. Add a child and the load moves even better, etc.
I'm sure that others will respond with a much more technical explanation, however, it is not anywhere near as hard or complicated as it may seem.
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Hi, all! A round of recent video viewing on YouTube has freshened by childhood enthusiasm for the pre-Amtrak days of passenger trains (yes, I'm that old) and reminded me that I've always had a question about multiple-loco consists (if that's the correct term) and I've decided to sign up here and ask you folks about it. My question doesn't really depend on whether the lashup is all diesel-electric or a combo of diesel and steam (which I've only seen in rare videos) or whether the locos are all at the front or one is at the rear...it just seems to me that the throttles (or rheostats?) for each motor would have to be *perfectly* matched otherwise you'd have a situation where one loco is over-driving the other one...right? IOW, without some sort of connection to match up the revs, it seem to me inevitable that one loco would be either dragging or pushing the other...even if only slightly. Let's go back to the days of steam: two locos would have had no connection other than the physical hitch and there would have been crews in both cabs, correct? Would those engineers have to have constantly modulated the throttles so that the two were pulling in perfect tandem and not creating the situation I'm describing? Today, with diesel-electric (and lots of system connections) how is this managed? Thanks very much, everyone!
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